The First UK Cavity Wall Passivhaus - Denby Dale

The Denby Dale Passivhaus - first cavity wall Passivhaus in the UKOver the last 10 months, the construction arm of Green Building Store - Green Building Company - has been building what has come to be known as 'the Denby Dale Passivhaus' - the first certified Passivhaus in the UK to be built using traditional cavity wall construction. Bill Butcher and Chris Herring report ...

Built for private clients in Denby Dale, West Yorkshire, the project is all 8m2, 3 bedroom detached house, built to a tight budget of £141 k. It received its Passivhaus certification at the end of April, one of the first 3 projects to go through the Passivhaus certification process with Pete Warm of WARM: Low Energy Building Practice.

The Passivhaus diaries

The project has already attracted much attention throughout its build, in part due to our Passivhaus Diaries blog about the project. Following every stage of the build, the blog attempts to provide an accessible, technical guide to Passivhaus construction techniques, suitable for the layperson and professional alike.

Cavity wall construction

Another reason the project has attracted such interest is its application of Passivhaus methodology to UK cavity wall construction techniques. European construction is commonly solid masonry with external insulation and render or timber frame, and so Passivhaus buildings often use one of these two methods. For a number of reasons, and perhaps controversially, we decided to stick with familiar cavity wall building methods and materials for this project. This was for the following reasons:

• Masonry wall construction, including cavity wall, contributes to a high thermal mass within the insulated building envelope - allowing a more even living environment, in terms of both acoustics and temperature. Through use of dense concrete blocks and concrete ground­floor slab within the thermal envelope, the house will have a greater thermal mass, stabilizing temperatures and optimizing passive solar gains.

• Cavity wall construction is the method that we, in the UK, are most familiar with. We wanted to build a Passivhaus using traditional construction techniques with, as far as possible, materials you could find in any local builder's yard.

• West Yorkshire planning rules require natural stone facing on the exterior of new buildings and so ruled out the option of block-built construction with rendered finishes.

(Photo above) the completed building.

However, by deciding to use cavity wall construction at Denby Dale, we undoubtedly made things harder for ourselves. We were going into uncharted territory. Although we have heard of some cavity wall Passivhaus projects in northern Germany, there is little technical documentation readily available about them. So, in effect, the team had to start from scratch. To meet the airtightness requirements of a Passivhaus, cavity wall construction relies on wet plastering as the airtightness barrier. It might have been more straightforward to go down the timber frame route, which can achieve airtightness by lining with vapour barriers and airtightness tapes etc. By using cavity walls we needed to work out new detailing, particularly around the junctions of elements such as floors and roof to walls.

The experimental nature of our project inevitably did lead to a certain amount of anxiety through the build. Fortunately for us, it was a gamble which paid off, with final airtightness results at the Denby Dale Passivhaus coming in at O.33ach@50Pa. In the process of the build we have also developed some really excellent detailing which can be applied to cavity wall Passivhaus projects in the future, such as how to fit the windows into the cavity wall. The bespoke plywood boxes and aluminium cavity closers, we developed for this purpose, offer a robust and unique solution which make cavity wall a viable way of getting to Passivhaus standard. We had already been contacted by other Passivhaus project designers keen to go down the cavity wall route. We very much see cavity wall as offering an alternative option for Passivhaus construction in the UK, with timber frame and block and render offering equally valid solutions for achieving the Passivhaus standard - dependent on the specific needs of the project. There are many ways of crossing the river.

Professor Wolfgang Feist, originator of the Passivhaus methodology and founder of the Passivhaus Institut in Germany, has been supportive of the project and of the company's attempts to adapt Passivhaus design to cavity wall construction. He said,

“The Green Building Store team is to be commended for adapting the Passivhaus methodology to British building techniques and for constructing the first Passivhaus using cavity wall construction in Britain. The Denby Dale project has proven that Passivhaus design can be easily adapted to British building techniques. Airtightness is not a myth - the rules of physics are the same everywhere - and wet plaster offers an excellent airtightness barrier for cavity walls, if applied to all surfaces of external walls and connected properly at the joints. The Green Building Store team has done a great job at Denby Dale and also in helping to spread the word about Passivhaus design in the UK. Congratulations!”

Lots of careful detailing was needed to get a cavity wall design up to the exacting standards required of Faaslvhaue buildings.

Lessons from Denby Dale

We were pleasantly surprised at how relatively easy it has been to meet the Passivhaus requirements. We easily beat the airtightness requirement (0.6 air changes/hour @50Pa) by about 45%. We also managed to come in well under the space heating requirement of 15kWh/m2/annum, meaning that space heating costs are anticipated to be less than £75 per year.

Partnership working

Passivhaus and low carbon buildings require high levels of airtightness and close attention to thermal bridging. To achieve that level of attention to detail requires the design team, on-site workforce and client to all be educated in Passivhaus theory and practice. You have to create a team ethos where everybody understands their part in the process, where there is continuity of personnel, and ideally subsequent monitoring of the building's energy use is included.

Both of our businesses are very much in favour of the partnership approach to construction. As we know, individual subcontracting teams for different trades do not naturally 'look out for each other', leading to breakdown of the building fabric and energy use performance. A typical example of the problems that can occur on site would be a subcontracted plumber coming along and puncturing the vapour and airtightness barrier which is then covered up by the subcontracted plasterer.

Trust, honesty, transparency and commitment between all parties, at all levels and stages of the project, will go a long way to answering these questions. Good robust and buildable detailing is essential. An early inclusion of builder and any subcontractors in the design stages for the two-way exchange of. knowledge is preferable. We believe that partnering contractual arrangements - where contractors are chosen for their suitability at an earlier stage of the design process (often used for large complex projects) - could be a useful model for Passivhaus projects.

Above: two stages of the cavity wall build showing the foamed glass for below DPC (top) and the rockwool insula­tion above DPC.

Minimising thermal bridging

Understanding and modelling thermal bridging is becoming absolutely critical to predicting the heat loss of a building. Measures include:

• Use of 300mm insulation in the cavity, going right down to the strip foundation, so that any heat lost from the concrete floor slab will have a longer thermal transfer path.

• Use of lightweight aerated block below ground level, which does not transfer heat as readily as standard concrete block.

• Use of basalt and resin cavity wall ties (instead of the usual steel ties, see left).

• Positioning of windows and doors at the centre line of the insulation layer.

Maximising airtightness

Passivhaus buildings require very high levels of airtightness (O.6ach@50Pa). The Denby Dale Passivhaus' design and construction pays particular attention to junctions, which are always difficult for airtightness because of the differential movement between different materials. Measures include:

• Wet plaster coating to interior walls.

• Concrete floor slab is carried across the top of the blockwork of the inner leaf of the wall to minimize shrinkage cracking between the wall and the floor

• Attention to airtight detail around window and door openings and junctions between floors, walls and roofs, including use of airtight membranes and tapes.

• To improve airtightness around the window opening, a plywood box was set into the wall. An adhesive-backed airtightness tape was then attached to the plywood with a fleece wrapped into the wet plaster, making the junction between the plywood and plaster airtight. Another airtightness tape was used to seal the gap between the window and the plywood box.

• Various details at first floor junction, to avoid penetration of the inner leaf blockwork including: use of timber wall plate; parging of the blockwork behind the wall plate; use of-anchored stainless steel threaded bar to carry the 302mm timber I-beam structure. Use of l-Bearn for first floor had the added bonus of allowing us to use void for MVHR ducting and all other services, further helping with airtightness (and aesthetics).

Minimising 'thermal bypass'

Thermal bypass refers to air movement through or around insulation, which can reduce its effectiveness. Although not a requirement of Passivhaus design, addressing thermal bypass - by reducing air movement through or around insulation - is becoming good building practice. For the Denby Dale Passivhaus this meant design detailing for windtightness and careful installation of insulation.

Super insulation

Super insulation is fundamental to Passivhaus construction, along with close attention around junctions of these elements. Measures include:

• Walls: 300mm fibreglass batts

• Under groundfloor: 225mm polyfoam insulation

• Roof void: 500mm fibreglass quilt

• Windows and doors: triple glazing with insulated thermal break in frame.

Mechanical ventilation with heat recovery (MVHR)

MVHR is an absolutely integral component for achieving the necessary performance levels needed for Passivhaus buildings. It allows for sufficient and comfortable ventilation to all areas of the house, whilst minimizing the loss of heat gained from the

sun, human activity, cooking, showering, electrical appliances etc. This is achieved by the use of a sophisticated heat exchanger driven by two very efficient fans. The incoming air is blown past the outgoing air and is used to heat the incoming air. This has the effect of saving over 90% of the heat that, due to uncontrolled ventilation and draughts, would be lost in a more 'conventional' house.

A blockwork built Passive House

Key data for the project

• £ 141 k build costs (excluding motorized external sun shading. decorating. garage. external works and incoming services)

• 118m2 three-bed detached house

• Minimal heating - using 90% less energy for space heating than the UK average

• Anticipated heating costs of less than £75 per annum

• Airtightness = 0.33ach@50Pa

• Space heating needs = under 15kWh/m2/ annum

• Peak heating load = 10W /m2 (when outside temperature = -10 degrees C)

• Total heat demand = 1.18kW (equivalent to one bar of an electric fire)

• Condensing boiler heat output = 4.8kW (it was impossible to find a boiler with smaller heat demand)

• Mechanical ventilation heat recovery (MVHR) unit - heat recovery efficiency of 92%.

The future

Having gone through the Denby Dale process, we feel, more than ever, that Passivhaus is the way forward for the UK. It can help create quality, comfortable buildings while also achieving 90% cuts in occupants' heating bills. It offers the UK an easy win solution towards the massive cuts in CO2 emissions we need to make - urgently. We are keen to apply our experiences at Denby Dale to both new build and retrofit projects and are currently researching, using PHPP, a Passivhaus retrofit to a 1930s house. Green Building Store is also expanding and strengthening its Passivhaus products and services including: construction, consultancy, training, and Passivhaus products.


The balcony sunspace (above)

Lancaster Cohousing Project

The Lancaster Cohousing project is a certified Passivhaus/Code for Sustainable Homes, level 6 and Life Time Homes, affordable community housing project. It has evolved through a participatory design process with the individual householders and Eco Arc Architects. In this article Andrew Yeats and Graham Bath provide an overview on the wall construction, and first floor construction, with particular regard to the integration of Passivhaus detailing. Work on the largest certified Passivhaus cohousing project in the UK has progressed well since the article in the previous issue of Green Building magazine. The project, when complete, will consist of forty one individual households, ranging from one bed flats to three bed family houses, along with shared community facilities.

The Lancaster Cohousing project, from its conception, has aimed to be a cutting edge example of sustainable design and living. The decision to design and certify all homes to Passivhaus standard ensures a rigorous approach to the energy performance of the buildings, with attention to detail to ensure continuity of the insulation throughout the external fabric with minimum cold bridges at junctions of elements or penetrations through the fabric for doors and windows etc.

Super insulated wall construction types that were considered at the outset of the project

Eco Arc has been building 300mm wide super insulated cavity walls (originally with Peter Warm and David Tasker with imported Danish wall ties) since 1992, initially at York Eco Centre & Heeley City Farm. From the same time period we have been building 300mm wide super insulated Masonite l-beam timber frame constructions, with the first one being David's House in Wales. Our projects have been featured in previous issues of this magazine. However, we had not built to the exacting Passivhaus standard before. We decided to go back to basics and prepared eight wall type construction options (each described/illustrated below) for project team review.

1. 500mm wide masonry cavity wall with 300mm insulation in cavity with render or timber boarded external finish.

2. 200mm solid stud timber frame (type A) over clad with Driffutherm & render external finish.

3. 300mm timber I-beam stud timber frame (type B) with timber boarded finish.


4. 300mm plywood web timber frame outer leaf & 140mm blockwork inner skin / render finish.


5. 300mm plywood gusset timber frame outer leaf and 140mm blockwork inner skin / boarded finish.

6. 300mm plywood gusset timber frame wall detail/ boarded finish.

7. 300mm adhesive applied external insulation & render finish with 140mm masonry blockwork inner skin.

8. 425mm solid clay block wall with Perlite integral insulation and 40mm external insulated render.

The wall types finally selected

After much deliberation and discussion (with some strongly held views by various parties) within the project team of the pros and cons of the eight wall options on the table, along with a thorough cost review and program review of the consequences of each option, we settled on the traditional cavity wall. Interestingly, with one of the timber frame options we would have saved 10 weeks in the overall construction program, but even allowing for the reduced contract preliminaries it would have cost £80,000 extra to the total projected contract sum.

The contractor was particularly keen on the cavity wall option as the north of England seems to be dominated by traditional masonry trades. Graham Bath had watched Bill Butcher's Denby Dale video several times and gained the confidence he needed to train his team to deliver the same Passivhaus exacting standard in Lancaster.

The cavity wall option would not frighten off the locally available tradesmen, it would allow us to build in some thermal mass and it was the cheapest option on the table, allowing us to deliver more affordable homes to the client group. We also understood the key disadvantages; relating to construction quality control for good performance being hard to check and manage on site, and the need to work hard to design out traditional thermal bridges, with having some structure inside and some outside.

Although the cavity wall was generally agreed upon (Figs. 1 and 2), it was clear the wall facing the river to the south elevation was going to be mostly door or window and the small gaps between would be best as timber frame, so a 9th option was developed with Ramboll, the project engineers, for a 38mm wide, 300mm deep, Kerto structural timber frame panel system, insulated between the studs and externally insulated with Pavatherm Plus wood fibre insulation and clad with Operal fibre cement/ cellulose board (see Fig 3).

The key details to note, that enhance this conventional cost effective cavity wall detail up to Passivhaus standard, are described below.

Fig. 1. 300mm insulated masonry wall construction/externally insulated window head detail.

300mm wide cavity, full filled with Dritherm 37 (or in some houses Dritherm 32) recycled glass, soft mineral insulation. To give an effective wall U-value of 0.12W/m2K and 0.10W/m2K respectively. Initially we started with three rolls of 100mm wide insulation, with staggered joints but had expansion problems with the roll distorting the green block work over night in the damp air. We changed to two layers of 150mm which alleviated the problem.

Basalt Teplo wall ties, which surprisingly don't transfer heat across the cavity and don't figure as a cold bridge in PHPP.

Independent and separated internal and external lintels over openings. We looked at GRP combined lintels and cavity closers, but this simple separated detail worked out much less expensive.

Partial 18mm WBP ply box to close the cavity to the back of the window head. Interestingly both the engineer and contractor wanted to take the ply box right across the cavity to tie both leaves together but Alan Clarke and Nick Grant calculated in PH PP/Therm it would amount to 1.0kWh/m2yr heat loss a year through the linear cold bridge and would cause us to fail the Passivhaus target for certification. Air tight tapes seal the back face of the window head to the ply box, which is then concealed with the skimmed plaster board soffit.

Externally over insulating the window head and window reveal with 75mm EPS insulation up to the front face of the window unit, combined with the partial ply box, reduced the cold bridge Psi value down to a good value of 0.01, which was acceptable in PHPP.


Fig. 2. 300mm insulated masonry wall construction/externally insulated window cill detail.

Setting the window unit back 165mm from the face of the wall was the optimum location in terms of reduced shading for the soffit over hang, whilst still being towards the middle of the insulation zone, and being partially isolated from the cold outer leaf wall elements.

The use of high performance Passivhaus certified externally insulated/aluminium clad window frames provided by Greensteps, using the German Gutmann window alu frame components with 48mm and 52mm triple glazed low E, argon filled glazing with a glass U-value of 0.60W /m2K, with an Insulated Thermix Spacer PSi value of 0.036, giving a window frame U-value of 0.80W /m2K, and a total unit installation U-value of 0.9W /m2K. Initially we had problems with the Secure By Design requirements, which required laminated glass to all ground floor windows which both reduced U-value performance and the g-value of the glass, but the police ALO relaxed his requirements in some areas due to the high level of neighbourhood watch provision inevitable within a cohousing scheme.

The windows have been tested to 1350 Pa (equivalent to force 14 and 102mph wind speed) for water-tightness and they weren't leaking when the test was stopped, which indicates the units will be extremely air tight under normal conditions.

A clever Wetherby Render APU rail allowed for a wind and water tight, flexible seal at the junction of the external through colour render and the external face of the aluminium frame to the window units.

As above the partial 18mm WBP ply box was used to close the cavity to the back of the window cill. This was combined with insulating below the window cill with Pavatherm Plus insulation up to the front face of the window unit. This reduced the Psi value down to a good value of 0.016, which was acceptable in PHPP. Air tight tapes seal the back face of the window cill to the ply box, which is then concealed with the window board set in to a rebate at the back of the window.

Down to DPC level around all the house perimeters, below a consistent window cill dado line, the external wall render was substituted with Eternit Cedral weatherboard cladding on battens. To ensure the cavity insulation remained in a wind tight void to avoid thermal bypass, the external air porous blockwork was protected with a wind tight barrier of Proclima Solitex Wall Wrap.



The infill timber frame walls to the south elevation was developed as a 38mm wide x 300mm deep Kerto structural timber frame panel system, with OSB sheathing, fully insulated between the studs and externally insulated with 100mm Pavatherm Plus wood fibre insulation and clad with battens & Operal/Cedral fibre cement/cellulose cladding board.

Over insulating the window head and window reveal with 100mm wood fibre insulation up to the front face of the window unit reduced the cold bridge Psi value down to a good level, which was acceptable in PHPP. Air tight tapes seal the back face of the window unit to the Proclima Intello vapour control layer over the Kerto structural frame with the taped joint concealed with the skimmed plasterboard reveal.

Setting the window unit back 160mm from the face of the wall was the optimum location in terms of reduced shading for the soffit over hang, whilst still being towards the middle of the insulation zone, and being partially isolated form the colder external elements. To avoid any services penetrating though the internal air tight barrier, or the insulation zone, a 25mm battened out service void was created behind the plaster board inner skin.


One of the requirements of Passivhaus design is 'thermal bridge free' details. The heat loss through poorly designed junctions can exceed that through the actual floor, roof and walls when they are insulated to Passivhaus levels.

Fig. 4 shows the thermal performance predictions at the wall junction (head and reveal) developed for this project. The problem we have is the transfer of heat from the warm inside through the weak link in the connection details around the window to wall abutments. The solution was to bring the window head inboard in to the depth of the cavity insulation zone and over insulate the window unit with 75mm EPS insulation. Although not often seen in the UK this is a standard Passivhaus detail on the continent. The Therm analysis provides an accurate prediction of the heat loss through the junction using detailed numerical analysis to 'solve' the steady state of heat loss and temperature throughout the construction, hence the 'isotherms' of equal temperature on the diagram. Using the results of the analysis we calculated the thermal bridge factor in terms of watts/m/K, and added in the estimate of the total heat loss in PHPP.

As most energy conscious designers/builders will know by now, supporting the first floor joists by bedding them in to the inner leaf of a cavity wall is a cardinal sin and a guaranteed way of creating multiple air leaks around the perimeter of the building. At Eco Arc we have been using perimeter ledger plates bolted to the wall for 20 years as an alternative, but not realising air can still escape behind the ledger plate through the porous holes in the block work in to the cavity. At Denby Dale, Bill Butcher finally nailed the detail in an air tight robust Passivhaus manner by parging behind the ledger plate first to seal the porous surface of the block wall, and ensuring the fixing bolts are stopped before fully penetrating the inner leaf of block work in to the cavity. On this project we adopted this tried and tested detail.

As with any Passivhaus we needed to accommodate extensive MVHR duct work. Using open web posi -joists to form the intermediate floor gave us more scope for routing ducts, cables, and soil pipes through the floor without having to have bulk head boxings to the ceiling below, or core drilling the webs of every I-beam floor joist.

Interestingly as shown in Fig 5 the structural formation of the steel webbed joist allowed us to cut away the bottom flange in critical locations to allow us to gain the required fall in a waste pipe without impairing the structural integrity of the joist.

Problems discovered and overcome on site


Originally the project design included for open cathedral ceilings within the insulation zone on the slope of the pitched roof from eaves up to the ridge level. As part of the inevitable post tender value engineering phase, we reluctantly agreed to drop the vaulted ceiling to flat ceilings to realize a cost saving of £177,000 across the project to get back on budget. In the original design, the project engineers at Ramboll had sensibly allowed for a single 100x100 RHS gable wind post within the inner leaf of block work from ground floor slab level to ridge line at the end of each terrace.

It was only with the erection of the first terrace on site, with the new design of flat ceiling, did we realize (in horror) that the old wind post was still in the engineer's design, penetrating through the flat ceiling insulation zone, creating a terrible cold bridge. After sweating palms for a while and Alan, Nick and Peter Warm running several Therm analysis trials through various parts of the cold bridge, did a mitigation solution emerge? With the problem exposed the structural engineer was able to design out the wind post above the insulation zone on future terraces, and Whittle Construction duly cut down the remaining un-installed wind posts left on site to make sure it did not happen again.

Airtight tapes not sticking in wet conditions

Once we were wind and water tight with the first new house in terrace A, Paul Jennings & Mike Neat set up an airtightness induction training day for the project team and key Whittle Construction operatives on site. It had became clear early on in preparation for the day that many of the ply window boxes had been taped when wet and the junction of the block walls to the ground floor slab had also been taped in damp conditions. Consequently, the stickiness of some of the tapes were starting to fail. Some even had to be removed and Mike Neat invested in a room heater and a hair dryer to locally dry out the substrate before re-taping and resuming the door air blower tests on a house by house basis.

Article by Andrew Yeats and Graham Bath


Green Building, 24. Summer 2012

The builders' experience so far

Following our selection as preferred contractor for the Lancaster cohousing project we were embraced by the client and their consultants into the project team at an early stage. Whilst the fundamental design principles had been established, we were able to contribute to the practicality of the detail. design throughout a regular series of team meetings during the 12 months prior to commencement on site.

These project meetings enabled us to understand the philosophy of the client and their design team to achieve Code for Sustainable Homes, level 6 and Passivhaus accreditation. Whilst we had carried out various schemes for housing associations throughout the Northwest to CSH level 4, the project brought new and exciting challenges, particularly due to the utilisation of masonry construction, rather than the more usual timber frame or prefabrication solutions. One of the primary requirements of the Passivhaus Standard is to achieve an airtightness level of 0.6m3/hr/m2 @ 50Pa and with the current Building Regulations at l0m3/ hr/m2 @ 50Pa this was seen as the major challenge on the project. We had, for some time previously, been achieving level below 5.0 and as low as 2.2 but the Passivhaus requirement set new standards.

In conjunction with the design team we selected an air testing company and appointed an 'airtightness champion', both With Passivhaus experience, to advise and assist in achieving this rigorous standard.

The Airtightness Champion is employed full time on site to install all air barrier membranes, taping, and to carry out air leakage tests at critical stages of the construction. He also oversees the activities of all other trades during this process to ensure and maintain the integrity of the air tightness and thermal barriers.

We are presently approaching plaster stage on the first properties so we await our first full preliminary air test, while will be carried out as soon as one house is plastered, but air leakage checks previously carried out indicate that we are on the right track. The traditional two coat wet plastering provides the primary air tightness barrier with pre-installed proprietary tapes and seals at all junctions, changes of direction and entries. Extensive parging is also being carried out to the blockwork behind services, timber supports, bearers etc which overlaps with the plaster basecoat.

One other defining aspect of the progress on site has been the process required to resolve day to day queries which often require the consideration of various members of the design team to ensure that Passivhaus standards are maintained, particularly with regard to thermal breaks airtightness etc... Whilst this has affected progress on the early plots we are confident that the steep learning curve experienced will prove beneficial during the construction of the remaining properties.

Graham Bath of Whittle Construction Ltd 

Building Tight, Ventilating Right

Ventilation, in all its forms, is about a lot more than fresh air. As homes become ever more airtight there is the irony that increasing thought has to be given to how they are ventilated, since a constant supply of fresh air is vital for the health of both the occupants and the building’s fabric.

Without ventilation, there will be a build up of condensation, pollutants and odours and the safe and sustained performance of some combustion appliances cannot be guaranteed.

Importantly, be the homes new build or retrofit, the ventilation has to be controlled: as the adage goes it is about building tight, ventilating right. Effective ventilation must be achieved by design rather than accident and the latest revisions of Approved Documents Part F (Means of Ventilation) and Part L (Conservation of Fuel and Power) of the Building Regulations, which came into force on 1 October, underscore this.

Part F and Part L are intrinsically linked explains Lee Nurse, chairman of TEHVA’s (The Electric Heating & Ventilation Association) ventilation committee and marketing director at Vent-Axia. “Both documents include a number of major revisions that include minimum energy efficiency levels for all ventilation systems. The launch of Part L’s new Domestic Building Services Compliance Guide highlights ventilation performance levels. Here for the first time a specific fan power requirement of less than 0.5 watt/sec is included for intermittent fans used in new build developments.”

To further lower dwelling emission levels, homes need to be increasingly airtight but not at the cost of good air quality. Changes to Part F include guidelines for airtight properties with infiltration rates tighter than 5m3hour/m2 at 50pascals. Where intermittent or passive stack ventilation systems are employed in airtight dwellings the guidance increases background ventilation rates by 50 per cent.

Nurse believes this looks set to cause some developers to re-evaluate their designs and move any new planning applications away from intermittent fans since the previous provisions in Approved Document F 2006 have already been difficult to achieve when using trickle ventilators in windows. “Our belief is that new regulations will clarify any grey areas to ensure that, as buildings become more airtight, ventilation levels are maintained,” says Nurse.

William Wright, energy and sustainability consultant at Inbuilt, is more circumspect. “The new Approved Document Part F gives many welcome revisions and guidance in specifying and commissioning. However, research on the old Part F has shown that ventilation issues were often ignored or poorly implemented in practice, causing indoor air quality problems. Good ventilation is as much about the implementation as the theory.”

Clearly housebuilders must now consider how the revisions will affect ventilation strategies and the impact on air quality and occupant comfort. As intermittent fans fall out of favour, changes to Part F and Part L look set to increase the uptake of continuous ventilation since it performs better in SAP (Standard Assessment Procedure), is easier to specify and easier to standardise, as trickle vents are not required.

In the short-term it seems likely that there will be increased adoption of whole house Mechanical Extract Ventilation (MEV) systems and decentralised Mechanical Extract Ventilation (dMEV) systems where individual fans in different rooms operate continuously. In the longer term, as airtightness requirements and Code for Sustainable Homes levels rise towards 2016, Mechanical Ventilation with Heat Recovery (MVHR) will become increasingly prevalent.

“MVHR or continuous extract can be advantageous in achieving current building regulations but MVHR will become practically indispensable in economically achieving the carbon savings for Code Level four,” says Wright. “As a broader understanding of issues around MVHR is gained by UK industry, it will more easily be designed into our buildings from the outset.”

Typically whole house, multi-room ducted MVHR systems combine supply and extract ventilation in one unit and use a heat exchanger to extract heat that would otherwise be exhausted to the outside.

Wright highlights noise, positioning of the unit and maintenance as key considerations. “If the fans are noisy, occupants may be inclined to try to turn the ventilation rate down or even turn the unit off.

The new domestic ventilation compliance guide gives particular attention to the issue in designing the ducts to be quiet. Ultimately, best practice may require baffling on the ducts as is sometimes used in Passivhaus and this can be quite bulky.

“With MVHR finding its way into apartments and smaller houses, due attention must be paid to where the unit is placed, with room for ductwork and consideration of noise issues. MVHR might need a dedicated cupboard in the dwelling if a particularly efficient, therefore large, unit is needed for Code compliance, although less efficient units can mount to the ceiling. The ducts to the outside air should be kept shorter for greater efficiency, which may mean mounting the unit in the roof void, assuming there is one,” explains Wright.

When it comes to maintenance there is one particularly worrying issue to consider. The NHBC Foundation review, ‘Indoor air quality in highly energy efficient homes’, states: “Recent BRE discussions with UK manufacturers of MVHR systems suggest that there is no market for replacement filters with several reporting no filter sales at all. This suggests that maintenance is not being undertaken – even at the most basic level.” Wright says air filters must be replaced regularly to maintain efficiency and prevent build up of pollutants. “The occupants need to know how to do this or it must be scheduled by the maintainers. Housing associations will need to think about accessibility of MVHR units for maintenance. An operation and maintenance manual will be distributed to private occupiers, but how many will take on the obligation to maintain the system over the years?”

John Kelly, marketing manager at Airflow Developments, says MVHR units are becoming increasingly more efficient, recovering over 90 per cent of heat generated within the building that would otherwise be wasted. “This is usually the damp extract air from the wet rooms – kitchens and bathrooms – of a dwelling. What would normally be lost is, in fact, a valuable resource to warm the fresh, filtered incoming air from outside and distribute it to the living areas of a dwelling.”

MVHR reduces excessive moisture in the air so it combats condensation and subsequent mould growth, saving money on long and short-term maintenance and decoration. The resulting better indoor air quality also has the dual health benefits of reducing microscopic fungal growth and eliminating the conditions in which house dust mites thrive, both of which are linked to allergic reactions and asthma.

Kelly warns that care needs to be taken when selecting a heat recovery system. “It is important to ensure that this is combined with an air distribution system that enables it to operate with optimum efficiency. Ducting, pipework and fixings must be of high quality and installed correctly.

“Traditional methods like flexible ducting are easily torn, high on system resistance and are often squeezed around bends and between joists, further reducing air flow. Likewise, plastic flat ducting is often ill-fitting, with sharp bends causing dust traps, time consuming to install and wasteful of materials.”

Another key feature to be aware of is ‘summer bypass’ and, at Inbuilt, Wright warns that not all units provide this. “Summer bypass means that heat is not being brought back into the building when not needed. However, we have come across several MVHR units coming to the market that omit summer bypass as a cost saving exercise.

Summer bypass is not explicitly required by building regulations, and omitting it could cause significant overheating problems in summer leading to complaints from purchasers.”

Another point to consider is that, for the first time, Part F requires post-completion testing of ventilation equipment to ensure it not only delivers the required airflow, but does it efficiently and quietly. “Post-installation performance policing is critical to ensure air quality in increasingly airtight homes. This is especially important with the increased adoption of highly efficient ventilation systems, like MVHR, which require trained competent installers,” believes Vent-Axia’s Lee Nurse.

Traditionally it has been the electrical contractor who has installed ventilation equipment. One interesting consequence of the new Regulations is likely to be a change in the contractor base because, with the pipework required for ducting and the knowledge and calculations needed to comply with the Regulations, the skill set is much more akin to plumbing.

Bovis Homes is one housebuilder which often employs MVHR. Michael Black, group development director, says that the company has sought to ensure that it has the most efficient systems installed whilst, at the same time, ensuring their operation and maintenance requirements are not difficult for its customers.

“In fact, we’ve just completed drafting an installation guide with a major MVHR manufacturer to assist our site teams and subcontractors in ensuring that the systems are properly installed and commissioned.”

Roger Hunt.


Rosslare Passive House Scheme

Ireland has woken up to the Passive House. Seven years ago Tomas O’Leary built Ireland’s first certified passive house in Wicklow – a home that showed Germanic influences in looks as well as energy performance. A new development at Grange Lough, Rosslare, reveals that passive can be made Irish – both in terms of what they’re built with, and how they look. Grange Lough in Rosslare, Co Wexford is the country's first commercial passive house development, and as such it's a landmark in the story of Irish construction. This is the first time that a speculative developer has looked at the market and decided it wanted passive houses. Not only that, but the scheme represents perhaps the most Irish take on the passive house you'll find. Its design is traditional- it does not look German, and incorporates much of what you'd expect in an Irish house, even a chimney. Most especially however, it has been built using Irish products and Irish expertise.

The design team is Irish, the developer is Irish, the thermal envelope manufacturer is Irish, the company which is certifying the house as passive is Irish, and almost all of the technol­ogy used in the house - including the windows and doors - is Irish.

"The passive house is a German concept but I think it's very important to localise it," says passive house guru Tomas O'Leary, director of MosArt and founder of the Irish Passive House Academy. "In Rosslare, they decided from the very outset that they wanted a fireplace and they weren't willing to roll over and accept no for an answer. You really wouldn't know it was a passive house walking around. It's traditional and I don't mean twee by traditional- it's just got a lot of the components that Irish people like."

There are three separate forces behind this project - developer Michael Bennett, Donal Mullins of Shoalwater Timber Frame who de­signed and fabricated the thermal envelope, and low energy designer Seamus Mullins of Seamus Mullins and Co. Both Donal Mullins and Michael Bennett have been building tim­ber frame houses for the past decade, while Seamus Mullins has provided much of the de­sign know-how. He recently completed the certified passive house designer course with the Irish Passive House Academy. Throughout their working relationship, the team has grad­uated to incrementally more efficient homes. The day we met in Rosslare, Bennett was fi­nalising the sale of an A3 rated house in another of his developments in Enniscorthy.

With rising energy prices and the recession fo­cusing minds on the energy performance of their homes, Bennett believes that the time is right for this kind of development. But location is also vital- Rosslare Strand has long been a summer holidaying Mecca. "We won't have first time buyers here," says Bennett, adding that the first house in the development carries a price tag of €490,000. "We'll have I expect retiree-type clients, with maybe an odd one re­turning from overseas, but as the houses are three and four bedroom, we are also catering for families and permanent residency." Given this profile, it was always vital that the house wear its passive tag lightly. "The Irish are very slow to change," he says. "If you built a state of the art glass house, would you sell it to any­one? I don't think you'd have a hope. People would come and look at it and ooh and ahh over it but they wouldn't buy it."


Giving the house a traditional look isn't all about meeting the market's aesthetic expec­tations. Irish houses need to be designed to cope with Irish conditions. "We've higher wind-speeds than mainland Europe, it's not as cold but we've more rainfall," Seamus Mullins explains. "The moisture levels mightn't impact so much on the thermal efficiency of the house but it will impact on the quality of the build. The detailing in Europe stands up in Europe but when it's put into wind-driven rain situa­tions; suddenly you're going to start getting leaks." Moreover, the design incorporates ele­ments of Irish design that have always made sense. The draft lobby, for example, is a stan­dard feature of many of the houses in the area.

There will eventually be eight houses in Grange Lough, which is a very private wall en­closed site. "There will only ever be one house for sale here at a time," says Bennett. The de­sign and construction team have however been very careful to ensure that early arrivals won't be living on a building site. All services and preparatory work for the eight houses are in place, all footpaths and roads have been constructed, while sites due to begin later are now landscaped and will remain so until con­struction can begin. Come construction time, the houses will be built behind hoardings, and as Seamus Mullins is quick to point out, the en­hanced sound insulation of a passive house means noise is unlikely to be an issue.

The first challenge facing Seamus Mullins was achieving the right orientation for eight houses on an elongated, restricted site. "If you haven't got a front elevation facing south, you've a rear elevation facing south," he says. "So it's a matter of changing the internal room layout. Nearly all of the four designs have a central core around the stairwell that faces south." Glazing to the west had to be amended due to over­heating issues turned up by the PH PP software. The houses themselves are not large by recent standards - the designs vary between 1,860 square feet and 2,200 square feet. "They're not large," says Mullins. "That's an important aspect as well, because to comply with passive certification there's a ratio of floor area of around 35m2 per person ... That's to try and get a better use of land, money and space." When he began his timber frame business eleven years ago, Donal Mullins of Shoalwater set out to ensure that any work that could be done in the factory was done in the factory. In order to preserve quality and continuity, the team that manufacture the frames also erect them onsite. He says that when he began building timber frame houses almost thirty years ago, the first panel taken from the back of the lorry was always the last to be used, and invariably suffered from constant handling. Bearing this in mind, Mullins developed a process of packaging the building system in bales and, and loads it to ensure minimal handling. "The first panel you take off should be the first panel you use." He says.Extreme attention to detail has been the hall­mark of the build. Achieving passive certifica­tion was vital to the commercial success of the project, says Bennett. "We had to be certain of our certification before we started. Anyone starting to build a house like this without their homework done and all their planning and all their issues addressed are on a hiding to noth­ing. There's no way can you get passive certi­fication without it." To facilitate this, the house was built on paper long before a sod was turned onsite. Because of all that preparatory work, says Donal Mullins, the construction stage didn't throw up any real stumbling blocks. "I wouldn't say there were huge issues during the build," he says. "The big issues were in the learning curve itself. Because of all the work we had done previously, we had a base of knowledge to build from." All three have been continually attending seminars and conferences in order to up-skill and keep abreast of best practice.

Achieving and then keeping airtightness is of course the perennial bugbear of low energy construction. It helped in Grange Lough that no subcontractors were used, and that many of the trade’s people had been working with Bennett for more than a decade. "If you don't bring your trades people along with you, if you don't educate them, if they don't know what they're trying to do, how in the hell can they work towards it?" says Michael Bennett. "We've done a lot of work on our people here."

Responsibility for achieving airtightness in the first place fell to Shoalwater, who have won an excellent reputation for themselves in this field using the Pro Clima system of membranes, tapes and adhesives. "When we were finished, we did our first blower door test," Mullins ex­plains. "We got an air change rate of 0.51 [ACH at 50 Pa]. That was very good. Then Michael could go and say to his electrician, his plumber, this is our airtightness, this is what you have to have when you guys are done. If it goes up, it's because of something you guys did. Now they're far more conscious and far more care­ful." A blower door test after each phase not alone kept tabs on how the air change rate was being maintained relative to the passive house standard of 0.6, but also revealed who was re­sponsible if the number went up.

One key issue that arose was with the Stovax stove. The blower door test immediately fol­lowing the installation of the stove drove the air change rate above the 0.6 threshold. Re­peat visits from Stovax improved the door sealing, which is where the problem lay, and moved the rate back down to acceptable levels. Surprisingly, the unit is still not a room-sealed unit. Though most of the air required from combustion is piped in externally, a small pro­portion is still taken from room air.

A potential issue also arose with the Beam cen­tral vacuuming unit. Though bin and turbine are both located within the sealed envelope, air could theoretically have escaped through an extract pipe which terminates outside the house. "We could have had a problem there," says Seamus Mullins, "but we were never going to find out if we didn't put it in. From a clean­ness and dust elimination point of view, the central vacuuming system is superb. The filtering system really fits with the passive principle in that you're creating this quality comfortable living environment." The solution which Beam came up with was a motorised valve, kept shut while the unit is not in operation, and triggered to open when switched on. The blower door test however u

ncovered no leakages in the system so the valve was not fitted.

The windows are from Munster Joinery's Fu­ture Proof range. "Passive house windows gen­erally cost people about €650 a square metre:' says Brendan Harte of the company.”We wanted to bring the price down, we wanted to put value for money into the market but still achieve the passive house standard. The glass section is 52mm triple-glazed and the PVC pro­file that we went with in Rosslare is a 90mm section, fully foam-filled all the way through." Two Munster Joinery windows are currently with the Passive House Institute in Darmstadt undergoing certification. The Passive House In­stitute was heavily consulted during research and development of the window range to en­sure that the onerous certification requirements would be met. The windows are the first Irish products submitted to the institute for certifi­cation. "I think that's very exciting because windows typically are the most expensive ele­ment in the passive house:' says Tomas O'Leary.”They're often imported and I think in these times, if we can generate local employment in construction, that's better for everyone."


"People are amazed when they hear that the windows are Irish, says Seamus Mullins.”Peo­ple think we should have Austrian or maybe German windows, we shouldn't have Irish win­dows, and are surprised to hear of the product range advancements that Munster Joinery have made." But using local products isn't just about local pride, says Donal Mullins. ''That window is a brilliant window and we can get it in Ire­land in a two week delivery date. It's so much easier to run a schedule when your window manufacturer can have them in ten days to two weeks, at this quality and with an Irish fit­ter. You've got any kind of little latch or lock problems, you ring him up and the serviceman is here." One of the most interesting findings of the project was in relation to cost. Seamus Mullins tracked expenditure throughout, and pre­sented a paper at the SEAl See the Light con­ference in Croke Park last September. He found that the cost of upgrading a project from A3 to passive came in at 02 per square foot. "That's in our first attempt:' he says.”We should be able to pull that down." The Grange Lough house is currently awaiting confirmation of its BER, which Seamus has calculated at high A3. He refers to Bennett's A3 house, just sold in Enniscorthy. "The funny thing is both the pas­sive house and the Enniscorthy house are A­-rated. In Rosslare, the running costs for all your heating and hot water, are going to be in the region of €500 - €600 a year, on the basis of an energy demand of 10 kWh/m'/a, while in En­niscorthy, the A3 rated houses is going to have an energy requirement of 67 kWh/m'/a - which is approximately six times more. It might not be six times more expensive to heat, but if it's three times more expensive, that means the Enniscorthy purchaser is spending an extra 0,500 to 0,800 a year for the life of that house."In order to meet the passive house standard, the house must be designed to have an annual heating demand of not more than 15 kWh/m'/yr. In Rosslare, the calculations are coming in at 10 kWh/m'/yr, 33% below the standard. Michael Bennett explains that they needed to aim high in order to provide sufficient comfort to ensure that certification would be achieved. "But we're going to get better at this, and more efficient at it:' he says. Being the first passive house in the scheme, everyone involved in­vested a huge amount of time and effort in achieving the right results. Bennett sees this time as an investment in skills and experience, and believes that from here on in, each house will go up within three months.

These houses are finished with the high end of the market in mind, but Bennett believes that it's entirely possible to provide the same qual­ity of build for the lower end. "I would hope, if not this year then in two or three years down the road we'll be starting a small scheme some­where. Ten or twelve houses, and they'll be 'white deal passive', to give passive certified houses to entry level buyers." Donal Mullins agrees. "Why not get into a position where we can supply passive houses at affordable prices to the county councils?"

What do you do after your insulation has been fitted? Make sure it's properly sealed up to ensure your home is airtight, writes Mark Stephens

You've been told many times about the need to insulate your home to a high standard. This is indeed by far the most cost-effective way to lower your fuel bills, not to mention comply with the energy requirements of the building regulations. But insulation and airtightness go hand in hand. After the insulation is fitted, an airtight membrane/ vapour control layer must be applied to the warm side of the insulation, otherwise all the hard work you put into insulating and protecting your home will literally leak at the seams! Airtightness, or 'air-flow-control' (a term that takes into account the risk of condensation as well the air exchange rate), is often associated to highly energy-efficient homes. But that's not always the case. In fact you can make your house airtight with standard trickle vents, or 'hole in the wall' ventilation. With regards to the building regulations, it doesn't matter which ventilation system you choose because during the airtightness test all of the vents, extracts (be they mechanical ventilation, trickle vents, passive stack, etc.) and chimneys are required to be sealed. But be aware that too little ventilation in an airtight home will invariably lead to moisture and mould problems. Where there is no mechanical ventilation, the wall vents are the only means of moisture management and this may not suffice! When sealing the building envelope to achieve a good airtightness standard the moisture generated in the home (as well as airborne pollutants/gases) requires a direct exit through mechanical ventilation or wall ventilation in each room. So if you are only relying on trickle vents for ventilation, it is good practice to open your windows to the front and rear of the home for 30 minutes two to three times a day as this will clear moisture from the building.

Your 'airtightness strategy' will need to be conducted very early on in the process and take into consideration moisture management. It is essential that all members of the construction team understand the process involved in maintaining airtightness; it's very easy for an electrician for example to cut an opening in the airtightness membrane for his cable without then resealing it. It is therefore highly recommended that your builder ensures that every subcontractor on site understands the process. And if you are a self ­builder it is up to you to ensure that your subcontractors seal any penetrations as they go, otherwise the end result is likely to be poor and require remedial works to pass the regulatory standards currently applicable.

The first step is to take pen to paper. Get the plans of your building and place a pen at a start point of your choosing (internally on the section) and then draw a continuous line around the entire building where you will have a continuous airtight envelope. Any potential air leaks are when you have to pick your pen up from the paper, and as you may have guessed, particularly prevalent areas for air leakage are dormer windows, roof lights, windows, doors, junctions between floors and walls, loft hatches, etc. The rules for creating airtight seals at such junctions are as follows:

• When the membrane meets a block wall (at a gable end for example) you will need to use a proprietary mastic to seal the edge of the membrane to the blockwork. It is important to emphasise that standard cavity blockwork is not airtight until it is plastered. Therefore it is recommended that the blockwork is plastered with a scratch coat prior to using the mastic.

• Where the membrane overlaps or meets a smooth or hard surface, you can seal the membrane using proprietary tape.

Remember to think about every single section of your building. It's easy to see that your pen would lift off the paper when a floor meets a wall; this is another critical junction and the solution for maintaining airtightness depends on the type of floor construction. For a hollow core floor it is recommended that a section of airtightness membrane be laid on top of the wall on which it is to be placed. The membrane then wraps up the side and over the top of the hollow core flooring; the blockwork for the upper floor is then laid on top of the membrane. This section of 'wrapping' membrane is then fixed to the wall or vertical membrane. In the case of a timber floor, you have two alternatives. You can either use the hollow core floor technique or you can use tape to seal around each Joist to a plastered wall.

In the case of timber frame construction, you will have to fix an airtight membrane internally on the entire envelope. In standard plastered blockwork, cavity walls are typically considered to be airtight as long as they are plastered externally and internally with a minimum of two coats (scratch and finish). Potential air leakages occur where the walls are penetrated (with doors and windows for example) and adequate airtight sealing has not been considered at these junctions.

As for cavity blockwork construction-it is now common practice to insulate walls internally with insulated plasterboard (normally a 50mm board with 38mm insulation and 13mm plasterboard) but this may not necessarily be airtight as the junctions between the boards may not be sealed adequately: a skim coat does not provide an airtight barrier, nor does plasterboard tape!

The solution therefore is to scratch coat the blockwork walls first and then fix the insulated plasterboard. You will still need to pay particular care at window and door reveals to ensure the airtight barrier is maintained by applying an airtight seal or using proprietary tapes. The main thing to remember is that your structure is not airtight at junctions where you are only relying on the thickness of the finishing coat of plaster.

An alternative method for applying an airtight barrier to a cavity blockwork construction is to apply a similar technique to a timber frame wall. That is to batten the unplastered internal blockwork wall and then to apply the airtight membrane to the battens. As well as creating an airtight envelope you are also creating a cavity for any services such as electrics or plumbing, thereby eliminating any chasing. The final stage then is to apply the membrane over a cross-batten and then plasterboard and skim.

While mould growth used to be associated with badly insulated homes, now it's often due to airtight homes with poor ventilation

What the building regulations say.

Building a home that is airtight will not only improve comfort, it's also an essential component of the building regulations'. It is now a legal requirement for any new house to be air-pressure tested; both ROI and NI currently have the same air permeability requirement of l0m3/(h.m2) at 50Pa. This figure basically says that an air leakage of no more than 10m3 per hour per m2 of building envelope area (at a pressure differential of 50 Pascal between inside and outside the building), is permitted". Compliance is verified by doing a blower door test; this is where a door or window is removed and replaced with a blower fan. The house is then pressurised (both positively and negatively) to measure the air leakage from the airflow rate through the fan. This identifies the pressure differ­ence between the inside and outside of the building structure. The bigger the number the worse the result; greater than 10 fails the building regulations, less than five is doing well, less than three is quite good. Bear in mind that the airtightness results will have a significant impact on the A to G rating you will get under your Energy Performance Certificate / Building Energy Rating.

*In ROI refer to building regulations' technical guidance document Part L and in NI the building regulations' F1 booklet.

**Air Permeability (q50) and Air Changes per Hour (n50) are two different measures: air changes are based on the volume 01 the building instead 01 the envelope area. Air changes are often quoted to demonstrate the airtightness 01 a building but this is not the measure used by the building regulations.

Illustrated guide - Airtight Walls

 At the floor junction, note how the membrane continues and is sealed down to the floor: the critical Junctions when fixing the membrane using this method occur where the membrane meets a penetration such as an opening or where it meets another material such as at a floor or a gable.

 Roof member/beam: Detail showing how to seal around a roof member to the airtightness membrane.

Cables: You will need to comprehensively seal every cable penetration to ensure airtightness. Some manufacturers provide a specialist tape that is more supple and easier to fold around cables than the standard, thicker tape.

Ventilation: Here we see the sealing around the pipework for a mechanical heat recovery ventilation system in the ceiling; this applies to all sorts of piping (vents, water, etc.).

 Open fires: A standard open fireplace is frowned upon in an airtight construction: at best an open fire is only 5%-20% efficient and even a multi-fuel stove will extract some of the heated air in the room in order to ignite the fire. Therefore in a 'super airtight' house, you must ensure that the air which feeds the fire comes from the outside; you can now obtain specifically designed multi-fuel stoves that address this issue.

A tale of two houses

House 1 

House 1 

You don't have to spend a lot of money to build a home that doesn't need central heating - what's required is the right specification and the correct installation. Patrick Waterfield finds out what it's like to inhabit an energy efficient space, in a family home in Co Down and in a holiday house in Co Donegal

House 2 

House 2 

Received wisdom tells of a law of diminishing return where insulation is concerned and thus an optimum level based on purchase price compared to the cost of energy saved. This is true up to a point - the point at which a central heating system is no longer needed! Then the whole equation gets tipped on its head because you save the cost of the heating system, as well as the fuel it would have used over the lifetime of the building.

The No Central Heating standard was designed with this concept in mind, developed by the author of this article and by a local timber frame company specialising in energy efficient dwellings (whose standard product consists of a highly insulated fabric with high levels of airtightness and mechanical ventilation with heat recovery). Arriving at the No Central Heating standard was 'simply' a matter of improving the fabric insulation further and specifying high performance glazing, as well as ultra-low air permeability levels.

The result is a system which, for little overcost on normal construction, can achieve levels of performance of Passivhaus standards. A number of house-building systems are available, notably from other European and Scandinavian countries, which provide excellent levels of energy performance but at a considerable cost premium. Key to the cost effectiveness of the No Central Heating system is the use of industry standard components, such as 140mm timber stud, and local factory and on-site construction. Additional costs for insulation, glazing, mechanical ventilation and high levels of airtightness are offset by the avoidance of a central heating plant (such as boilers) and heat emitters (for example radiators) plus associated pipework, valves and controls.

The walls, roof and floor of the No Central Heating houses are of layers of insulation of different materials, in order to provide excellent thermal performance without the risk of interstitial condensation. All windows, including rooflights and glazed doors, must be inert gas filled, triple glazed units with low emissivity coatings and insulated spacers.

While both the Co Down and Co Donegal houses share a similar fabric make-up and services (no boiler or radiators of course!) one is continually occupied and the other intermittently, which gives us a chance to assess the dynamic as well as steady-state performance of the system.

The mechanical ventilation systems continually extract air from the waste areas (kitchens and bathrooms) and recover up to 85% of the heat content which is transferred to the incoming fresh air. In this way, the dwellings benefit from continuous, filtered fresh air with a greatly reduced energy requirement and improved comfort levels. The system thus also acts as a means of transporting heat around the house, and is sufficient to heat the bedrooms and ancillary rooms to the required comfort levels. In most conventionally-built dwellings this mechanism would not work - the heat loss through the building fabric would be too high and there would also be too much air leakage in and out of the building. But in a super-insulated fabric with very low air permeability it can.

The homes are oriented towards the south, with high areas of glazing on the main facades, thus making use of available solar heat gains directly into the main living spaces. These, combined with heat from cooking, equipment and even people ­collectively termed "incidental gains" - contribute significantly to the heating of the dwelling. Again, in a normal house, these incidental gains would be insignificant compared to the rate of heat loss. However, combined with very low heat loss from the fabric and through ventilation, the incidental gains reduce the "heating season" to around three months, half that of a normal house. Additional heat, when it is needed, is provided by a room heater in the main living area, where higher comfort temperatures are usually required. The mechanical ventilation system, as explained above, helps to distribute this heat throughout the dwelling.

Integral to the concept of these low energy homes is the provision for intermittent heat into the bathroom areas, which also require a slightly higher temperature than elsewhere in the house. This can be provided by a towel radiator, either electric or wet - in the latter case being run on a small pumped circuit off the hot water cylinder. Sensible time control of the towel radiator will limit energy and cost consumption and does not dilute the No Central Heating concept. Furthermore, most of the heat generated in the bathrooms is thus distributed, via the ventilation system, to the rest of the house. Use of masonry walls around the room heater acts as thermal mass, helping to store heat generated and also acting as a heat sink to reduce the risk of overheating in summer - though high insulation levels also reduce excessive solar heat gains into the building.

Co Donegal

Construction type

One and a half storey timber frame

One and a half storey timber frame


0.l3W/m2K for walls, 0.11 W/m2K  for roof,  0.11W/m2K for floors and 1.0W/m2K for window units 0.l3W/m2K for walls, 0.11 W/m2K for roof,  0.11W/m2K for floors and 1.0W/m2K for window units

Airtightness < 2 m3/(hm2) at 50Pa

House size 2,000 sqft1,700 sqft

Energy rating BA2

Space heating heat recovery ventilation pre-heatsheat recovery ventilation pre-heats air; 5.5kW wood-burning stove;air; 4.5kW wood-burning stove with bespoke towel radiators fed by hotback boiler; towel radiators for water system, both approx.bathrooms fed by hot water system - 100W in size200W and 400W in size

Hot water heating Approx. 6m2 of flat plate solar36 evacuated tubes supplemented by panels supplemented by an air the stove with back boiler source heat pump (COP of 3)


House 2

House 2

The County Down house

The County Down House, which is owned and occupied by Darren and Ashleen Annett and their two young children, sits on a site between Darren's parents' house and that of the parents of Darren's long-term friend and architect John Lavery. The house comprises a main open plan living/dining/kitchen area, plus additional first floor living room, three bedrooms, two bathrooms, a study and a utility/shower room.

A plasterer by trade, Darren was more aware than most people of the opportunities for influencing all aspects of the design of a dwelling, including the energy side. He was also open to considering innovative products and practices - within cost constraints-of course. As the design phase took shape Ashleen was expecting their first child and the cost factor became even more important in their minds. The prospect of removing, at a stroke, the single greatest running cost of most houses, appealed greatly to them both.

The house faces more or less due south, fortunately dictated by the tight site, and incorporates a high level of glazing on the south facade and correspondingly low levels on the north side. The only fixed source of heating in the home is a wood-burning stove, located in the main living room. During the last severe winter, the timber frame provider became concerned for Darren and Ashleen and rang them to check that they were warm enough. He needn't have worried! Even with outside temperatures around -10°C, internal temperatures were maintained around 20°C. Ashleen reports that they needed to light the wood­burning stove most days for three months during the winter. This required a certain level of intervention, which perhaps would not suit everyone. However, the same heat input could be provided readily by, say, a wood-pellet burner with automatic ignition start, controlled on a timer.

Unlike the Co Donegal house the wood burning stove provides heating only, the solar hot water panels (located on the main roof pitch) being supplemented by an air-source heat pump. The heat pump comes as an integrated package with the hot water cylinder and can be controlled on time and/or temperature to fill in the gaps left by the solar panels. This approach has the advantage over the Donegal house of separately controlled heating and hot water systems. As with the Donegal house, small towel radiators in the bathrooms are run off a loop from the hot water cylinder.


Naturally, the heat pump runs on electricity and represents a certain energy and cost component (the latter of which can be reduced if operated on a night rate tariff). Darren reports that their electricity bills are around £40 a quarter more than normal, which also includes the ventilation system fans. However, some small gains are made through savings in lighting, which is almost all LED. Overall, the cost benefit is clear, the additional electricity cost being far outweighed by that of running a central heating system in a standard (or even well insulated) new build property.

The saw-tooth profile indicates day to night readings. Even during the coldest part of the winter from mid-to-end December 2010 (outside temperatures about -5°C) the internal temperatures are maintained at 18°C to 20°C, occasionally rising much higher when the occupants demanded it. The high variation in temperatures is due to the heating system not being controlled.

House 1

House 1

The County Donegal House

The house featured here was the prototype of the No Central Heating House and was built for myself and family. The house is intermittently occupied, being used currently as a second home. It faces southwest, to avail of views and solar gains while also addressing privacy with respect to neighbouring dwellings. High levels of glazing are deployed on the southeast and southwest facades and correspondingly low glazing ratios on the other sides.

The house comprises three bedrooms, plus a study/bedroom and two bathrooms, in addition to open plan living/dining and kitchen areas and a large porch. Heating for the whole dwelling is provided by a small wood-burning stove located in the main living area, which is open plan to the dining area and kitchen. The stove is fitted with a back boiler which produces hot water, fed via a simple gravity system to the hot water cylinder. This complements, seasonally, an evacuated tube solar water heating system located on the south-west roof pitch. Indeed, the two systems complement each other so well that the electric immersion back­up has never been used.

It was always intended that towel radiators ­either wet or electric - would be installed in the bathrooms. During the past cold winter, it was found that, in running the wood burner sufficiently to maintain comfort conditions in the living area, an excessive amount of hot water was produced ­there being no means of separately controlling the two outputs from the stove. Wet towel radiators were thus installed into the bathrooms, run off a pumped circuit from the hot water cylinder. This had a triple effect - not only was a heat leak provided for the hot water cylinder and comfort temperatures improved in the bathrooms, but the distribution by the ventilation system of heat from the bathrooms reduced the load on the wood burner.

Lighting is all LED, mostly "warm-white" 4.5W downlighters, which provide a similar light output and quality to halogen fittings while using a fraction of the energy. Of course LEDs produce much less heat than incandescent lamps. However, it is a much more efficient strategy to let the heaters produce heat and the lights provide light.

The intermittent occupancy of the house means that it takes a little while to warm up on first arrival - but this is of the order of a couple of hours after firing the stove, rather than a couple of days in the case of a standard masonry built dwelling. The house is built in an exposed location facing the Atlantic coast so you might expect us to get lots of noise, but the high level of airtightness, combined with very well draught proofed triple glazed windows, makes for an almost eerily quiet interior, even when the westerly winds are blowing their hardest...

Cost considerations

In order to build a dwelling that's comfortable to live in and does not require central heating, you will need to bear in mind two major cost considerations: the extra insulation and the triple glazing required to achieve the necessary thermal performance. Other costs such as mechanical ventilation with heat recovery (MVHR) and solar water heating might have been incurred in any case on a conventional build, although both are central to the concept of the No Central Heating house - the MVHR because it preheats the home and the solar collectors because there is no boiler to produce hot water.

I would estimate a cost of about £4,000 for the solar panels, £4,000 for MVHR, £4,000 for the additional insulation (above the cost of complying with the building regulations), and £2,000 for the higher specification on the glazing (overcost as compared to building regulations compliant double glazing), or equivalent in euros.

Towel radiator costs are minimal and stoves could have been specified as room heaters anyway, although prices were approximately £1,000 for the Co Donegal house and about £1,800 for the Co Down house.

Against this, about £10,000 is saved on a boiler and heating. In addition, the cost of fuel saved each year is likely to total £1,000, so that means that within about four years the extra cost of making your house thermally efficient will have been amortised. It also means that after this time, if you have chosen the central heating route, you will be paying more than if you hadn't!

An important factor with these two houses is that they were built without recourse to grants and full costs were paid for all components and systems, although the Annetts were able to avail of the (soon to be defunct) Low Carbon Homes scheme two-year rates rebate. This shows that ultra low energy housing is affordable - indeed, the No Central Heating system has also been used recently in six social housing units in East Belfast, with the promise of very low running costs and a considerably reduced risk of fuel poverty. Following the County Down and Donegal houses, two other private houses of this specification have been completed with more underway.

As we draw ever closer to the Government's target date of 2016/17 for "carbon neutral" new dwellings, all new housing will need to adopt these principles. Self-builders in particular can move well ahead of legal minimum requirements and future-proof themselves against rising energy costs by adopting this concept. The experience of these houses shows that it works not only in theory but in practice, with very little impact on lifestyle except for a greatly reduced carbon footprint and low energy bills!

Note: All costs include supply and installation but note that these are very rough estimates. When calculating your payback you should also consider the electricity cost of running the MVHR fans and, if there is one, of running the heat pump, though these should each be under £lOO/year or €lOO/year, where relevant, for the equivalent to the dwellings featured here .

The house was occupied for one day around 20 Nov 2010 and from 29 Dec 2010 to 1 Jan 2011, during which time the wood burner was fired up. The occupied period was not during the very coldest part of the winter and the wood burning stove was not run at its highest output. The impact of the heating system can be seen during occupancy; when the house is vacant internal temperatures follow outside temperatures. Night time losses during unoccupied periods are high because no curtains were drawn. Note that the impact of solar gains on the internal temperature are reflected in the spiked profile indicating day to night readings.

Patrick Waterfield is a Chartered Engineer and a Fellow of the Energy Institute based in Belfast,

Cold damp house transformed by Passivhaus retrofit refurbishment


A 1940's semi has become the first building in the UK to both reach the Passivhaus retrofit standard and be certified by a UK based certifier. Low carbon engineering consultants Encraft were appointed by housing association Orbit House of England to retrofit one of its 14,000 homes as part of a pilot scheme.

The housing association hope to learn how adapting existing properties to Passivhaus and other low carbon standards will help slash tenants’ energy bills.

The 1940s semi in Elliott Drive Wellesbourne, Warwickshire, is expected to see heating consumption drop by around 85% as a result of the £100k project. Not only is it the first building in the UK to achieve EnerPHit (Passivhaus retrofit) certification from a UK certifier– it is also the first Wimpey no-fines (sand free concrete) construction house in the world to achieve the standard.

The Elliott Drive house was one of a number of speedily built properties built to tackle the post war demand for new housing whose construction is well known for creating condensation, providing poor insulation and thus generating high heating bills.

A 70 sq m house of this type would typically cost around £1,100 a year to heat, and Encraft estimates the transformed building should now cost just a couple of hundred to run.

The Passivhaus principle is to construct or retrofit a house to minimise its need for heating and cooling by maintaining a constant temperature through effective insulation, airtightness, triple glazed windows and the installation of a mechanical ventilation heat recovery (MVHR) system.

The project saw Encraft oversee the installation of improved insulation in the walls, roof and floor which involved digging out the floor to install 200mm of under concrete insulation and 200mm of insulation around the foundations to minimize thermal bridging. It also required raising the roof level to accommodate thicker insulation, installing new triple glazed windows and doors, attaching airtight rubber grommets around soil, gas and water pipes, installing Mechanical Ventilation and Heat Recovery and a small gas heating system. Although they were not strictly a requirement of a Passivhaus, it also involved installing a new kitchen and bathroom, and fitting solar PV tiles.

Energy reduction is being monitored by Coventry University and the savings are being compared with those achieved by the other half of the pair of semi-detached houses which Encraft also retrofitted but in a less extensive, more affordable manner.


A growing number of housing associations are keen to explore the benefits of Passivhaus construction and retrofit to enable tenants to reduce their heating costs and avoid or escape fuel poverty.

Encraft are also working with several other housing associations on Passivhauses and on a newbuild site in Coventry as part of a project to compare Passivhaus standards to Code level 6 on two adjacent properties on an infill plot donated by Coventry City Council.

Encraft Passivhaus consultant Helen Brown explained: “This project marks a turning point in the UK Passivhaus and EnerPHit sector. Not only is it the second EnerPHit project, and the first to be certified by a UK-based certifier, it has also achieved higher air tightness results than those required by Passivhaus standards, thus dramatically reducing energy bills for tenants.

“58 Elliott Drive was the first Wimpey no-fines house in the world to be retrofitted to this standard. It shows what can be achieved with this kind of building and how it can be applied to the rest of the UK housing stock.

This gives us hope that in these times of austerity and fuel poverty, we can really make a difference to thousands of families on a limited income, in a cost-effective way and with respect for the environment.

“Because the triple glazed windows remain at 17 degrees even if it is below zero outside there is no need for traditional heating such as radiators under the windows. The temperature remains constant and additional heat can be delivered via the MVHR system which has ducts to every room. Background heating can be fitted as an additional source of warmth but a 100 sq m house only needs a 1kw boiler compared with a 12 to 20 kW model required in a traditionally constructed home.”

Passive Attack by John Moorehead


All was not well when work began on this impressive Co Cork home and its architect had to pull out the stops to make the eco-home fit the brief

A problem with the design of a passive house in Co Cork made its designer, John Morehead, go hot and cold. A fault in the climate information, that was used to regulate the airtight, ventilated and draught-proofed house, meant the house was too cool. Passive house designs are so sensitive to the environment and climate that even heat from a plasma television can throw the controlled temperature off kilter.

Morehead, an architect with the Cork firm Wain Morehead Architects who specialises in designing passive homes, was concerned to get all the details right when he embarked on a new project on the shoreline of the upper Owenabue estuary, in Carrigaline.

Building had just started on the two-storey, four-bedroom family home and, while the greatest care had been taken to find ecological and energy-efficient materials, it was clear that everything was not as it should be.

“We commissioned the job of sourcing climate data to specialists in Britain,” says Morehead. “We were working off Dublin data, not local data, and suddenly we found we didn’t meet the passive-house criteria. By this stage, we were already on site. We didn’t eat for a week — it was that serious.”

It took three weeks for Morehead and his team to put the mistake right. Intensive research was carried out to try to find out what was putting the data out of sync. Readings put the house at a temperature that was far cooler than first anticipated. There was also less radiation, which can have a big impact on passive-house technology.

“It turned out there was a fault in the way the climate data was being generated,” says Morehead. “It operated on peak-data information — the extremes rather than the averages. To make the house passive again, we had to tweak the specifications. We did this with the help of a local climatologist, but it was three weeks before we were back on an even keel.”

The result, though, is an impressive and unusual contemporary house in a lovely setting with striking views. It is the home of Sally and John O’Leary and their three children. The couple approached Morehead about building an energy-efficient home in August 2008, and work began the following year. They had been refused planning permission to build a previous modern design on the site.

The refusal was based on context rather than aesthetics, and the fact it would be built on a sloping site that ran into the Owenabue estuary was also a concern.

Around that time a neighbouring house was being developed, so it was important for both the O’Learys and their new neighbour to maintain privacy and preserve views, as well as to keep the planners on side.

“Our brief was to design a four-bedroom family home and to be as ecologically friendly as possible while sticking to a budget,” says Morehead. “Our clients were interested in an energy-efficient home and one that would bring the outside space in, merging into the interior.

“The family also wanted natural finishes and a design that was relatively simple. There had to be a focus on food and cooking because that is what they love to do.”

Morehead came up with the modern yet simple passive house in Carrigaline, which was completed in April this year. It has almost 2,600 sq ft of living space over two floors. The home is at the cutting edge of passive-house design, and is one of six certified passive homes in Ireland. A name plate by the front door proudly displays its Certified European Passive House status.

The project did not begin with the intention of building a passive house. “It was originally intended to be an A-rated passive solar project and the decision was made to seek passive-house certification as late as the tender stage,” says Morehead.

Passive house certification is a quality-assured energy-performance and comfort rating that demands stringent control of both the design and construction process.

To make the most of the views and to accommodate the sloping site, the living area was put upstairs. It overlooks the estuary and contains a central winter garden, which enhances the notion of bringing the outdoor space in.

The area has become a multipurpose room, whose use changes with the weather and the seasons. “It is a busy spot, encouraging participation in activities by young children at the principle accommodation level, irrespective of weather,” says Morehead.

“The room is fully insulated from the remaining accommodation, so it can become an outdoor space without compromising the rest of the house or thermal envelope,” he adds.

“Both the expansive glass wall from this room to the hall and the screen to the deck fold away to make a versatile indoor/outdoor space penetrating deep into the bowels of the dwelling.”

Particular care was taken to ensure the home was as airtight and insulated as possible. A cement substitute made from the by-product of the iron and steel industry was used instead of conventional concrete, a decision that saved more than 16 tonnes of CO2. The walls were clad in panels of fibre-cement. It is a low-maintenance material, a consideration that was important in the coastal setting.

Because so much of the work was undertaken during the recession, Morehead and the O’Learys hired local tradesmen and builders when they could.

The upper walls and roof were made from closed wall timber-frames, also manufactured locally. “This construction had exemplary insulation and airtight characteristics,” says Morehead.

“These walls also assist with moisture transfer during periods of high humidity. The upper walls were covered with a rain screen of a carefully selected and detailed untreated Austrian larch cladding.”

To achieve a home that maximises heat gain, Morehead sought out technology to minimise heat loss. Triple-glazed windows with low-iron glass increase transmission of solar heat. The air temperature is controlled to such an extent that no internal surface temperature within the house deviates by more than 4C, even if it’s -10C outside.

The kitchen is an important feature for the O’Learys, who had stressed that they were keen cooks, and it has been given a linear corner window that not only frames views of the river, but also maintains privacy by preventing it from being overlooked by the neighbouring house. The room has direct access to the multipurpose area and the upper garden.

On the upper level there is also a guest bedroom, laundry, study and family room.

The brief had also asked that the needs of a growing family were taken into account. The house should adapt to the children as they grow. To meet this request, the children’s bedrooms surround a large, open multipurpose play area.

The kitchen, along with the living and winter garden areas, has an innovative infrared heating system that Morehead developed himself and is now patenting. “The infra-red emitters heat the occupant, not the air,” he says. “Therefore a level of individual comfort control can be enjoyed independently.

“As with the sun’s energy, 40% of which is infrared, the occupant and indeed any warm-blooded creature, absorbs and responds to this energy through their skin and their inbuilt circulatory system. Heat is then distributed evenly and at a pace to suit the comfort criteria of the body.”

Solar water heating comes courtesy of tubes at roof level and rain water is used for both sanitary and gardening use. While Morehead is coy about the overall cost of the build, he is keen to press home the savings that can be made on home heating, especially at a time when energy companies are raising prices.

“You can heat a home like this for just €150 to €200 a year,” says Morehead. “You are independent of all the price hikes and can live with consistent comfort levels.

“The project confirms that a carefully tuned passive solar design can meet the passive-house standards cost effectively.”

Zero Carbon Homes as defined by the Code for Sustainable Homes

Our built environment accounts for over half of our carbon dioxide emissions. We now have the Code for Sustainable Homes (CSH) to help designers and builders of new homes in the UK. But will it help or hinder? In April 2008 the government launched the Code for Sustainable Homes (CSH), calling it a 'step-change in sustainable home building practice'. The scheme that it replaced, and that it is modelled on (EcoHomes) failed to capture the imagination of the very conservative house building industry outside token projects, that were blessed with government funding and housing associations. Unlike EcoHomes though, the CSH feels much more like a mandatory, rather than an optional code. In fact they did a lot more than that because at the political level, at the time of its introduction, we were at the pinnacle of a housing boom, with massive demand for homes and a lot of potential new housing sites hanging in the balance.

The government used this almost unprec­edented demand to throw down the challenge. Permission would be given for new sites as the incentive (new eco towns), but adoption of the CSH is the mandatory side. Essentially, the feeling was that any volume builder, who could prove to be singing from the 'zero carbon home' song sheet, could expect to be favoured with easier planning permission. It sounded good for the shareholders, good news for home buyers and good news for the environment. But is it?

Well the answer has to be a guarded 'yes' because it has captured the imagination of many mainstream developers and the industry as a whole. However, on the downside, since the launch of the CSH we have seen unprec­edented levels of greenwashing. The most striking example is that many, very ordinary building products are being re-branded green, purely based on the assumption that they could be used in projects built to the CSH stand­ards. No Code level is mentioned but let's not forget that Code level 1 is barely better than current Building Regulations! Another example is industry trade groups claiming that all their members are now zero carbon but merely on the back of carbon offsetting! Are they now CSH compliant?

The true definition of 'zero carbon' has yet to be properly defined and big players in the industry have recently discovered that they may have bitten off more than they can chew by going along with the government's rallying cry of 'zero carbon by 2016'. This is an impossible goal and doomed to failure from the beginning, but we need to watch this space over the next couple of years for a further re-definition and a probable watering down of what 'zero carbon' actually means. For the time being though see the table below for the present definition. One concern is that it will get diluted in its requirements but not in name. For instance, there is a proposal on the table suggesting that builders who are unable to meet the zero carbon target by that time will be allowed to pay a fee. A fine, if you like, which, it is touted, will be used for carbon offsetting elsewhere. Therefore, one word of warning before we go on, what you read here may well not be what will actually be required in 2016.

Who it affects

Housing Association funded projects 2008-2012 Code level 32013-2015 Code level 4 Likely to require code level 6

Everyone else via Building RegulationsAssessment mandatory for all dwellings25% carbon improvement44% carbon improvement (below 2006 Building Regulations baseline)Proposed zero carbon homes

Another, more subtle and perhaps overlooked aspect of zero carbon is that, If aiming for level 6, builders (site owners) are having to enter the power generation business at a hopelessly uneconomic scale, which somewhat ignores the efficiencies of the renewables obligation certificate system (ROCs). At present it seems that on-site renewables will be eligible for tradable ROCs, which effectively renders them part of the national renewable generation grid and despite being on-site, adding nothing, or very little, to the national total. Feed In tariffs (that have proven so successful in other European countries) to encourage more on-site generation, may well have been a better route towards 'zero carbon' than ROC's, certainly at this small scale where plant costs are high and returns are low.

Zero carbon is not the only problem facing anyone wanting to achieve Code level 6. When you get to that level other difficult requirements also kick in, some of which are step-changes, such as increasingly stringent water use restrictions. The SAP (standard assessment procedure) software that forms the basis of the Part L of the current Building Regulations also underpins the energy category of the CSH.

Background to the CSH

The CSH was developed, at least in part, in response to the European Parliament's Directive 2002/91/EC on the energy performance of buildings, itself a response to Kyoto. In 2006 the government announced the 10-year timetable towards a target that all new homes from 2016 must be built to 'zero carbon standards'. This would be achieved through a step by step tightening of the Building Regulations. Since April 2007 the developer of any new home in England could choose to be assessed against the Code.

On the 16 November 2007 the government confirmed that it would be proceeding with the implementation of mandatory ratings against the Code for all new publicly funded homes, following responses to the consultation on making a rating mandatory. From May 2008 all homes built in England need to be rated to the CSH.

 The ‘zero carbon’ home (as defined in the code)

A zero carbon' home is where net carbon emissions resulting from all energy used in the dwelling is zero. This includes the energy consumed in the operation of the space heating/cooling and hot-water systems, ventilation, all internal lighting, cooking and all electrical appliances. The calculation can take account of contributions from renewable/low carbon installations on/in the dwelling, or provided by an energy services company (ESCO) on/offsite, provided it directly supplies the dwelling. Alternatively it is acceptable to include, in the estimate of carbon emissions, the contribution from 'accredited external renewables, For a true zero carbon home, it will also be necessary to ensure that the fabric of the building significantly exceeds the standards currently required by Part L of the Building Regulations. 2000 (as amended). The 'heat loss parameter' (covering the walls, windows and other elements of the building design) must be no more than 0.8W/m2K.

CSH uses the SAP (standard assessment procedure) computation which takes into account energy consumed through heating, lighting and hot water provision. Homes will have to reach zero carbon for these factors using the SAP computation. Heat and power for this element must be generated either in the home, or on the development, or through other local community arrangements, (including district heat and power) and must be renewable (i.e. non-fossil fuel) energy. A zero carbon home is also required to have zero carbon emissions from use of appliances in the homes (on average over a year). SAP does not contain any provision for energy consumption of appliances but will be updated to do so in due course. Until SAP is updated the 'appliances' element of the qualification will be that each home must provide an amount of renewable electricity equal to a specified amount of kWh per metre squared of floor space. This additional power must be renewable power, produced either within the area of the building and its grounds, elsewhere in the development or beyond, as long as the developer has entered into arrange­ments to ensure that the renewable generation is additional to existing plans. The amount of such additional power can be reduced by any surplus from the arrangements to meet zero carbon on heating, hot water and lighting.


Does Passive House Require a New Design Language?

Architect Paul McAlister

Architect Paul McAlister

The movement of building standards towards passive house and rising fuel prices are the main initiatives driving the construction industry in the direction of certified passive house standard within Northern Ireland. It is an attractive aspiration for us within the construction and design industry to be at the forefront of low carbon design and passive house design in Northern Ireland, whilst making positive contributions to C02 emissions. Fully pursuing this standard within this industry would also open up export markets for our knowledge, skills and products, however in any potential advance towards an implementation of passive house there are many issues to be considered. The first issue is the capital cost of a passive house build. It is not possible to put a figure on the extra cost for a passive house building over a conventional building which barely complies with the 2008 Building Regulations. This would be far too simplistic. Cost depends on a whole host of variables, which includes the private residential sector, passive house clients generally insist on high quality fixtures and fittings. For example, the extra cost for passive house standard windows over standard triple glazed windows, may be due to improved functionality alongside achieving the energy standard and the criteria of passive house certification.

Those taking up the challenge and aspiring to build to passive house standard should have a clear idea of the budget limitations surrounding their project and the space requirements that budget will deliver. However, many designs, despite the best efforts to optimise design and energy modelling, will always fall short of certification. Often additional improvements which move the design towards certification don’t quite make the passive house threshold for space heating demand of 15kWh/m2/yr. Having a heat demand slightly higher than the threshold, at say 18kWh/m2/yr may have slightly higher running costs, but they are minimal when compared with capital costs of finding the final 3-5kWh in some cases. Each individual project must weigh up their capital expenditure versus running costs to decide what is best for them. When the site condi­tions and design strategy produce a performance for heat demand that falls inside the passive house criteria then certification becomes a simpler process. However if the threshold is missed by a few kilowatt hours, resulting in the design being un­able to deliver the space heating solely through the ventilation system, it may be better suited to add a secondary heat source whilst still achieving a high performance building. With unusually cooler winters predicted for the coming decade, having some extra, user-controlled, heat contributors such as the addition of a couple of radiators may be beneficial.

Another issue of the application of passive house is design, which by its nature is subjective to the client and architect. A number of bespoke, architect-designed homes are being certified within Northern Ireland, which is a promising sight. However it is difficult to imagine standard ‘off the shelf’ designs being replaced with homes designed to optimise site and energy performance. Passive house can be adapted to every conceivable style of building with the emphasis placed by the passive house modelling tool on efficient building envelopes and internal layout and orientation. This could place added expense on those restricted to single storey buildings by planning. The proposition as to whether or not ultra-low energy buildings will require a new design language and how they will contribute to urban and rural landscapes is an unknown factor. It is important that planners are educated to recognise this new typology of building that may deviate in form from designs favoured today for example, by having a design that does not necessarily face the road.

The regulatory compliance, concerned with the recognition of passive house can be an issue. The two equivalent energy performance methodologies within building regulations have shared objectives to considerably reduce energy use, but actually have conflicting methods. Passive house comes with a difficult certification process, requiring air leakage testing after completion and evidence of installed insulation. It provides a model for inspection of low energy builds to ensure that adequate attention to detail is applied. Passive house prioritises minimisation of heat loss above all else, while the SAP methodology for Part F compli­ance is not as strict on fabric and ventilation heat loss but puts a high emphasis on the use of renewables. The English version of Part L 2011 came into effect in October 2010 with enhanced standards of performance required. A proposed solution to these conflicting methodologies is that the passive house standard could be recog­nised as an alternative method of compliance with the new Part L. This could provide a pos­sible strategic move by government to support the potential of the pas­sive house building sector by moving building regulation in line with the requirement of passive house certification.

The final issue concerns knowledge of pas­sive house building procedure. There is an education process needed to show how passive house standard buildings and its retrofit equivalent EnerPHit are achieved. The responsibility of propagating this information needs to be taken up by our enthusiastic designers and architects. It would be desirable if funding for research of new, more cost-effec­tive materials and technologies is secured and buildings already complete and in use at this standard should be monitored.

The point where every new building and renovation is a certified passive house may never become a reality, however it is not the attainment of certification that's important but the aspiration to go as far as is practical within the limitations of each project. It is therefore vital to accept no less than ultra low energy buildings in an attempt to make our entire building stock practically passive house standard; this would put into practice now what building regulations will eventually catch up with in the future.

Paul McAlister

House Design relieves the misery of Hay Fever

Architect Paul McAlister

Architect Paul McAlister

Cooking steaks on the barbecue, mowing the lawn or taking a walk in the countryside – all normal summer pursuits for many people.  But, for hay fever sufferers, the thought of uncut grass sends them rushing indoors.  Over 15 million people in the UK have hay fever and 95% are allergic to grass pollen. But what’s the alternative to a summer of sneezing, a runny nose and watery eyes apart from a box of tissues, antihistamine tablets or moving to the Sahara Desert?  Believe it or not, building a new home with “hay fever prevention features” may be part of the answer.

“Triple-glazed windows are very effective at keeping grass pollen out of the house in the first place but a unique ventilation system makes the biggest impact.  The hay fever sufferer then has a ‘pollen free oasis’ to live in,” explains Portadown architect Paul McAlister, Northern Ireland’s first Passive House Designer.

A Passive House is a specific approach to energy efficient homes, originating in Germany (Passivhaus).  The key features are super insulation, extreme airtightness, triple-glazing and a mechanical ventilation system.

“One of the key features of a Passive House is the airtightness requirement meaning windows do not need to be opened for fresh air.  Instead, a clever system called Mechanical Ventilation Heat Recovery supplies and circulates fresh filtered air 365 days per year.  The filters used are very fine and they stop minute particles of pollen from getting into the house making it a ‘pollen-free zone’ for the hay fever sufferer.”

Up to 80% savings in energy costs can be made by living in a Passive House even though the ventilation system uses electricity as a power source.  Heat is collected from the air leaving the house and this energy is then reused to heat incoming fresh air.

“I find the summer months a real challenge whether I’m indoors or outdoors, “ commented James Ervine, a chronic hay fever sufferer from Bangor.  “Even though I shut the windows and remain in a cocoon for several months, my eyes still itch and my nose runs.  The Passive House design sounds ideal for someone with my condition and I will definitely consider this approach when I build a new home in a few years’ time.”

So watching the high pressure settling over Northern Ireland doesn’t have to bring tears to the eyes of the hay fever sufferer any longer.  If you’re planning to build a new house and struggle with hay fever every summer, it’s well worth investigating the Passive House technology.

Author Paul McAlister