Passivhaus overheating shouldn’t happen: it’s one of the criteria of the international Passivhaus standard. Even so, people sometimes ignore this requirement during the early stages of the design process.
Anyone familiar with spending a hot summer's day in a caravan and then another in a stone house with closed shutters will appreciate the meaning of ‘Decrement delay’. The inside of the caravan closely maps the rise and fall in external temperature to provide the familiar stifling effect on the occupants .
Total primary energy consumed from direct and indirect processes associated with a product or service within the boundaries of cradle to gate. This includes all activities from material extraction (quarrying / mining / harvesting), manufacturing, transportation and fabrication until the product is ready to leave the final factory gate.
Solar energy is a seriously underrated resource. More power from the sun hits the Earth in a single hour than humanity uses in an entire year, yet solar only provided 0.39% of the energy used in the US last year.
Passive House is a building standard that is truly energy efficient, comfortable and affordable at the same time. Passive House is not a brand name, but a tried and true construction concept that can be applied by anyone, anywhere.
“As debate ramps up in Ireland about whether local authorities in Dublin should adopt the passive house standard, and the UK government scraps its plans for zero carbon homes, Dr Shane Colclough urges passive house advocates to prepare for the lobbying battles ahead by remembering the basic science behind the standard.”
Montgomery Primary School in Devon is the UK's first zero carbon, climate – change ready school. Andy Pearson takes a look at the fabric first, 'tea cosy' principles behind the design of this award-winning building.
When it comes to achieving outstanding results Montgomery Primary School, in Exeter, is top of the class. The UK's first zero-carbon school, it is also the country's first Passivhaus school and its first climate-change-ready school. If all that were not enough, this pioneering £8.9 m scheme was recognised by CIBSE at the Building Performance Awards 2014, at which it won the New Build Project of the Year award for schemes under £10m.
The zero-carbon target for the 420-pupil school was set by the client, Devon County Council, in 2008. The council had secured additional funding from the Priority School Building Programme - along with a grant from the Zero Carbon Task Force - to create an exemplar zero-carbon school that would help to increase knowledge and understanding of low-energy school design. The council worked with engineers Hamson JPA, and their architect and quantity surveyor affiliates at NPS Group, plus Exeter University's Centre for Energy and the Environment, to develop the design. The team set out to pioneer a new approach to primary school design. The simplest solution to meeting the client's zero-carbon aspirations would have been to construct a conventional Building Regulations-compliant building, which could be transformed into a zero-carbon solution using a biomass boiler for heat and hot water, and a green electricity tariff for electrical power. Such an approach was considered unsustainable by the design team.
'This solution is without value because it relies on the continued use of precious resources,' says the project's quantity surveyor, Chris Rea, from NPS Group. By contrast, Montgomery Primary School has been designed to minimise its use of resources, so that all energy for heating, lighting and power is generated on site.
“The space heating requirement of the school is now so small that the primary source of heat input is body heat from the pupils and teaching staff”
The starting point for the resource-lean design was to minimise fabric heat losses. The new two-storey school has been built within the grounds of the 1930s primary school it has now replaced. It is oriented north-south, with the majority of classrooms facing north and the more flexible teaching spaces to the south. A double height, central atrium-corridor divides the spaces. Passivhaus standards were adopted for the design of the building fabric. These set a limit of 120 kWh/m' /year primary energy use, and 15 kWh/m'/year for heating and ventilation - significantly lower than the 55 kWh/m'/year for a typical school. To meet the heating target, the school's walls have been assembled from highly insulated, precast concrete sandwich panels, comprising 100 mm of high performance, rigid foam insulation, sandwiched between a 100 mm-thick concrete inner leaf and 70 mm outer skin.
Concrete was selected for its high thermal mass, which was deemed essential in enabling the step-up from Passivhaus to zero carbon. Pressure to complete the 2,786m2 building in time for the school term forced the design team along the precast, modular route. At the time the modular fabric solution was being developed, building services design was not sufficiently advanced to enable these to be incorporated into the precast units.
On top of the precast walls is precast concrete roof deck, blanketed with 200 mm of extruded polystyrene insulation. Underneath the building is a 150 mm layer of expanded polystyrene to insulate the cast, in-situ raft foundation and floor slab from the ground. 'We've adopted the same principle as a tea cosy, with insulation placed on the outside of the building to allow the thermal mass of the concrete structure to be fully exploited,' explains Rea.
Compliance with Passivhaus standards has ensured the school is exceptionally airtight. 'We followed the maxim "build tight, ventilate right",' says Rea. An air-seal barrier layer was defined in the modular wall, roof and floor constructions at the outset In addition, construction joints were carefully detailed and unavoidable service penetrations and other openings were kept as regular circles or rectangles to match the pipe or duct, and to make them easier to seal. To ensure the detailing was flawless, regular workshops were undertaken with all members of the construction team; for some of the more critical details, samples were prepared and tested on site to verify their performance.
The team's efforts were successful. The Passivhaus air-leakage standard is o.6 air changes per hour at 50 Pa; the focus on air tightness at Montgomery has enabled the building to achieve an impressive 0.28 air changes per hour at 50 Pa.
The fabric-first approach dramatically reduced the space heating requirement of the school. In fact, this is now so small that the primary source of heat input is body heat from the pupils and teaching staff.
A mechanical ventilation system with heat recovery ensures optimal thermal comfort is maintained throughout. Warmed fresh air is supplied to the teaching spaces. This returns to the air handling unit (AHU) through a high-level transfer grille into the building's central atrium-corridor, from where a high-level grille allows the air to return to the AHU in the plant room. This enables excess heat to be moved from high-occupancy spaces to spaces with a lower occupancy and a demand for heat.
Top-up heat is provided by electric heating elements mounted in the air supply ducts. The electric elements are set to operate on manual boost or fabric frost protection only. To protect against overuse, the boost feature is restricted to returning the room to the design set-point temperature. The advantage of this simple heating system is that it has zero losses when not in use and is almost 100% efficient in operation. 'Using electric heaters enabled us to offset this electricity using roof mounted photovoltaic panels.' says Rea.
The ventilation system operates in two modes. In winter, when heat is required, the building is predominantly mechanically ventilated using a variable air-volume strategy under control of the Building Energy Management System (BEMS). This uses temperature and C02 sensors to control dampers to alter the volume of air supplied. The BEMS also varies the speed of the fans in the building's AHU to minimise expended fan energy, while keeping the system in balance.
Energy consumption in the AHU is further minimised by a reversing regenerator unit. This uses two metal heat-exchanger packs to absorb heat from the exhaust air stream, and a series of dampers to reverse the airflow through the unit mechanically, once every minute. Initially, warmed exhaust air passes through one of the aluminium regenerator units, heating it before it is discharged. Simultaneously, cold supply air passes through the other, warmed, regenerator unit, where it picks up heat before it is supplied to the school. After 60 seconds, the control dampers reverse the airflow direction so that the regenerator warmed by the exhaust air now imparts heat to the incoming air, while its twin is regenerated by the warm exhaust air stream. The system is claimed to operate with 93% heat-recovery efficiency.
In summer, the building operates on a natural ventilation strategy. Each classroom has manually opening, triple-glazed windows that allow cool, fresh air to enter the room. This fresh air drives stale, warm air upwards to the transfer grille, and out into the central atrium-corridor, where large roof Iights open under control of the BM S to create a stack-driven, low-pressure, ventilation system. The effectiveness of the design was proven by modelling using IES: Virtual Environment software.
Summertime overheating of the highly insulated school is mitigated by the high thermal mass of the building fabric. In extreme circumstances, the natural ventilation system can operate overnight to remove excess heat to pre-cool the thermal mass for the following day.
In the same way that the building fabric was modularised, so too are the building services. Early involvement of the building services contractor, NG Bailey, enabled the ductwork and lighting assemblies to be supplied as modules and lifted into place. To reduce the lumen output of the lighting, the rooms all have light-coloured walls. In addition, absence detection and daylight sensors turn off lights in unoccupied spaces to minimise energy consumption.
On-site renewable sources are used to enable the school to meet the zero-carbon, in-use target Photovoltaic panels were found to be the most appropriate technology to meet the school's predicted 166,000 Wh/y energy requirement. Around 900 m' of Sanyo HIT N-235 SE10PV of PV panels are located on the south-facing pitch of the roof. The electricity these generate is fed into the national grid.
Electricity generated by the PVs is not used to heat the hot water, although it is used for the trace-heating system, which keeps the water warm in the distribution pipe work. Instead, the hot water is heated throughout the year by a high-temperature, C02 air source heat pump, which picks up heat from the kitchen extract. Modelling showed this solution to have the lowest overall energy use of all possible options.
To enable the teaching and facilities staff to familiarise themselves with the innovative technologies and solutions employed at the school, the client specified an extended commissioning period in the contract. In addition, the team used the BSRIA Soft Landings approach for the handover and follow-up visits.
'The structure provided by this approach enabled the school staff, design team, client and contractor to work together to identify and resolve issues that - if left unsolved – would have compromised the school's low-energy operation and client's satisfaction with the scheme,' says Rea.
The design complies with the requirements of Building Bulletin 101: Ventilation of School Buildings. Unusually, the school has a 60-year design life. The scheme has been modelled by Exeter University and found to be sufficiently robust to ensure conditions remain comfortable, without overheating in the school, even as the climate changes up to 2080.
“The scheme is sufficiently robust to ensure conditions in the school remain comfortable. even as the climate changes up to 2080”
The scheme was completed in October 2011. Its measured energy performance figures are: 12 kWh/m'/year space heating and 167,358 kWh/ year total energy, including energy used in the kitchen. Despite these outstanding low-energy credentials the building has only managed a DEC band B because of its reliance on electricity for top-up heating. Monitoring has shown that, over the course of a year, the amount of electricity generated by the PVs is equal to that imported from the grid.
From the school's perspective, its carbon neutral performance means that the manager doesn't have to budget for heating and electricity costs over the coming year. Instead, any savings on the utility bills can be used to support future maintenance and educational budgets, to make the school a zero-carbon, self-sustainable, stand-alone environment of learning.
Pearson, A. (2014) ‘The full Monty’, CIBSE Journal, April 2014, pp. 4-8
The government's cynical recent energy policy announcements represent a dereliction of duty to the vulnerable and to future generations. There is an alternative, argues award-winning passive house architect Justin Bere - and it's beautiful.
Many of the UK's elderly citizens and low income residents cannot afford to maintain healthy conditions or basic levels of comfort in their homes, while those who are better off often cosset themselves in over-heated homes burning excessive amounts of precious and polluting fossil fuel. Everyone complains about the cost of energy, politicians wring their hands and try to sound as if they have a plan, but little is done to improve the UK's domestic and non-domestic buildings to make them more affordable to run.
"Those who peddle minor gestures in sustainability as if they are an alternative to passive house are either lacking in real knowledge, or simply playing confidence tricks on the public."
In a world where there is a rapidly growing population demanding a share of ever fewer resources, it is unrealistic folly and indeed utterly foolhardy to think that the answer to the high fuel consumption of our buildings is simply to outsource new power stations on guaranteed repayments to meet the unchecked projected future growth in demand. Yet this is exactly what the UK is currently doing. Through sloppy thinking, the UK is mortgaging the future; locking the younger generations into a level of expenditure on fuel that will most likely be completely unaffordable for them. Effectively they will be trapped in a situation with no affordable way out. What is utterly unforgiveable is that the reason for this is that the current generation doesn't want to feel any of the pain of transition. But transition will have to happen in the end and the longer we leave it, the more painful - or catastrophic - it will be.
Yet those of us in the passive house community have demonstrated that there is a solution that can deeply reduce overall energy demand in both new and existing buildings by 80 or 90% while at the same time creating exceptionally healthy and comfortable buildings. New passive house buildings can be built for little or even no extra cost if design priorities are realigned with an energy saving imperative. But even where there are additional costs, such as in passive house retrofits, the costs can be paid back in a lifetime so that future generations are handed an affordable and beautiful solution.
The UK can look back with pride at how its population pulled together and responded effectively to national emergencies in the 20th century. Once again, and as much as at any time before, we need to respond with effective action to what I believe is an even bigger emergency than those faced by previous generations.
Effective action will include re-building the respect for vocational skills, the passion for making things to the best of our ability and to world-beating levels of excellence. It will include renewed respect for world-class engineers and engineering businesses. It will include a transformation of the construction industry from one focussed on what it can take from society, to one focussed on what it can give to society.
All this requires an honest, clear vision which I believe all of us in the passive house community have, and which we must promote. We must point out that those who peddle minor gestures in sustainability as if they are an alternative to passive house are either lacking in real knowledge, or simply playing confidence tricks on the public.
In An Introduction to Passive House (RIBA Publishing, £27.99), I present facts and arguments that attempt to show why passive house is the best form of building for people's health, comfort and general well being, for every age group, for fantastically low energy use, for very low whole-life costs, for the environment as a whole and for the future of the planet.
Embracing passive house technical methods does not mean that we have to turn our backs on beautiful architecture or light-filled, flowing spaces. Passive building techniques give us the opportunity to hold on to the uplifting aesthetic tenets of the very best 20th-century buildings, while at the same time transforming our technical abilities to make social progress and beauty possible in a world where excessive consumption is no longer tenable.
An Introduction to Passive House shows that the economics of passive house are clear. While shifting priorities is a simple lifestyle choice for many, for others the help of responsible, intelligent and forward-looking governments is needed in order to make it easy for individuals and organisations to make steps now, for the benefits of both themselves and of society at large, now and in the future.
Passive house is emphatically not a product, nor does it require designers to use particular products. The Passive House Institute offers manufacturers technical assistance to improve their products, and provides quality assurance certification, but passive house buildings can be built without any certified products. Passive house is a standard and an advanced method of designing buildings using the precision of building physics to ensure comfortable conditions and to deeply reduce energy costs. It does what national building regulations have tried to do. Passive house methods don't affect "buildability", yet they close the gap between design and performance and deliver a much higher standard of comfort and efficiency than government regulations, with all their good intentions, have managed to achieve.
The in-use performance data from passive house buildings shows that to provide comfort, to save energy, to reduce bills, to protect people from fuel poverty, to reduce excess winter deaths, to save money in the long run and, arguably most importantly, to reduce CO2 emissions, it is difficult to escape the conclusion that deep, energy-saving passive house retrofits and new-builds must become the norm. A deep, energy-saving retrofit programme will create jobs now at the same time as saving money on fuel imports, both now and long into the future. Vast amounts of money can also be saved by reducing the need for new power stations and for long-term storage of nuclear waste, and by reducing the serious impact upon the National Health Service of the UK's dreadful, damp and draughty buildings.
In concluding I will repeat the question that visitors to passive house buildings seem to ask more than any other: Why aren't all buildings built like this?
An Introduction to Passive House by Justin Bere (RIBA Publishing) is available now at RIBA Bookshops (ribabookshops.com/passive)
Bere, J. (2014) ‘A Beautiful Solution’, Passive House + , Issue 5, UK Edition, pp. 20.
Many people appear confused about how PassivHaus and the code for sustainable homes can run in parallel, 'Does one compliment the other?’
To obtain the definitive answer, we need to remember that us that Passivhaus focuses on building fabric and performance without the use of renewable technology. Typically a PassivHaus will achieve code energy rating of level 4 or 5. This means that it is an ideal methodology for achieving the higher level of the overall code rating, whilst also minimising the cost of renewables.
Principles And Performance
The term 'PassivHaus' refers to a specific construction standard for buildings which have excellent comfort conditions in both winter and summer. These principles can be applied not only to the residential sector but also to commercial, industrial and public buildings. For houses, it is claimed that this is the world's leading standard in energy efficient construction. They are designed and built using a step-by-step approach with efficient components and a whole house ventilation system to achieve exceptionally low running costs to create something which is comfortable, healthy and sustainable.
There's an interesting article in Green Building Magazine www.greenbuildingpress.co.uk written by Justin Bere about a talk given in London by Wolfgang Feist who founded the German PassivHaus Institute in Darmstadt.
The fundamental objective of PassivHaus design is unambiguously to cut energy consumption and to provide accurate design tools to measure the expected energy consumption in a clear, accurate, numerical way. Germans really don't have time for vagueness and are aware of the requirements set out in UK Building Regulations. However many of our Code level features are incorporated, no one can circumnavigate the essential requirement to produce a building designed to use less than 15kWh/m2/annum supplementary heat and no more than 120 kWh/m2/annum primary energy [total of heating, lighting, hot water, appliances and any cooling). No box ticking wood chip boiler - nothing will let the PassivHaus architect, developer or builder circumnavigates this fundamental, verifiable bottom-line requirement for PassivHaus certification.
The simple techniques necessary to achieve PassivHaus design are: Insulation [typically 30cm thick]; PassivHaus windows [airtight, triple glazed with thoroughly insulated frames achieving an overall U-value of 0.8 including the frame]; Airtight construction [max 0.6 air changes/hr under 50 pascals pressure] with very efficient mechanical heat recovery ventilation. Assuming that these three main performance targets are met, together with detailing to eliminate cold bridging and numerous other detailed requirements prescribed by the PHPP software, it is possible to eliminate the need for a boiler and the need for radiators or underfloor heating.
Comparing certain other UK building codes with the PassivHaus approach highlights difficulties in the UK codes that have been introduced in relative haste. By contrast the PassivHaus code has passed the test of time and Dr Feist is very careful to ensure that it remains truly robust. It is the very robust nature of the concept and the software that led the RIBA in a sustainability review to originally describe PassivHaus as 'The emerging European Standard.' Now there are about 17,000 buildings have been constructed worldwide, typically achieve an energy saving of 90% compared to existing housing principles.
The NHBC Foundation and Zero Carbon Hub have published 'A practical guide to building airtight dwellings'. It brings together the experiences of those who have already got to grips with air tightness for the benefits of designers and builders who have not. It provides solutions for common air leakage paths. Clearly, changes in the Building Regulations have now made air tightness an issue which cannot be ignored.
The Denby Dale Project
Typically, PassivHaus buildings are built using timber-frame construction or blockwork wall with external render. Green Building Store has succeeded in adapting the PassivHaus approach to British traditional building methods - by creating the first certified PassivHaus in the UK to use traditional cavity wall construction. Earlier this year the Denby Dale PassivHaus project in West Yorkshire received its official PassivHaus certification.
The project - built by Green Building Store's construction division Green Building Company - has pioneered the combination of low energy PassivHaus methodology with standard British cavity wall construction and building materials. Bill Butcher, Director of Green Building Store, said, "We chose cavity wall construction because most British builders are familiar with the technique and materials could be sourced easily from any builders' merchant. Cavity wall also met Yorkshire planning requirements for stone exteriors and was affordable for our clients. In addition, masonry construction, including cavity wall, offers a 'cave effect' which acts as a thermal mass, helping to keep temperatures stable in winter and summer".
It requires minimal heating - using 90% less energy for space heating than the UK average; £141 K build cost for the 118m2 three-bed detached house. Green Building Store's technical film 'PassivHaus low energy building in the UK' for building professionals is freely downloadable from www.greenbuildingstore.co.uk. The 60 minute film covers all stages of construction of the Denby Dale project.
What are the challenges?
Achieving the required level of air tightness, minimising the risk through good design and specification.
Is it costly to build?
European experience suggests an extra 6% is likely. There are not yet enough UK houses to make a proper comparison, although BRE is advising on a London project which has achieved PassivHaus for the same cost as a typical social housing one.
Are PassivHaus products widely available?
Yes but windows have at present time to be imported; they have generally been the reason for higher costs.
Will adopting PassivHaus facilitate compliance with buildings regs and the Code for Sustainable Homes?
Yes. If a compliant design specification is derived from PHPP [the PassivHaus Planning Package] and transposed into SAP, a 30-45% improvement in carbon emissions can be realised - without the use of heat-pump, biomass or other low carbon or renewable technology.
To help stimulate the uptake of renewable technologies in Northern Ireland, Northern Ireland Electricity (NIE) will provide support for wind and solar photovoltaics (PV) following the closure of the Low Carbon Buildings Programme Stream 1 grant for renewable electricity technologies in early February 2010. The following grants are available from the NIE SMART programme which is managed by NIE Energy on behalf of NIE:
|Photovoltaics||£2,000 per kWp or 30% of the relevant eligible costs, whichever is the lesser amount (Max. £10,000)|
|Wind||£900 per kWp or 30% of the relevant eligible costs, whichever is the lesser amount (Max. £4,500)|
Funding will not be available for retrospective installations – only applications submitted from the 8th March 2010 will be eligible for funding from this new grant (PV applications submitted from 19th July 2010 will be eligible for the increased grant levels).
The guidelines for support are available below:
- NIE Household Grant guidelines
- Microgeneration Certification Scheme installers
- Microgeneration Certification Scheme approved products
Please note that NIE does not guarantee or underwrite the performance of any technology and it is your responsibility to ask accredited installers (or the manufacturer) what reassurances they can provide in terms of the expected performance of the system.
Clarification on the position of MCS products which are in transition NIE Energy will consider applications from customers who are using an accredited MCS installer (whose details are listed on the MCS website) and an accredited product (even if it is just noted on the MCS website as being in ‘transition’). We have had confirmation from MCS that products which are in ‘transition’ are at some stage in the MCS certification process but we must advise customers and installers that we will be checking each application with MCS to make sure that the manufacturer of the product is actively engaged in the certification process with MCS. Applications may be refused if, after checking with MCS, it is discovered that a manufacturer is not actively pursuing the MCS certification.
It is your responsibility to check with your local authority about whether or not planning permission is required. Please note that you must have received confirmation about planning permission before submitting an application for grant funding from NIE. If you proceed without planning permission then your application will be invalid and you will not be able to claim a grant.
Please note that farmers who are on a domestic tariff with NIE Energy will be eligible to apply for the grant but farmers who are on a business tariff are not eligible.
Please download an application form here and fill it in carefully – you must sign the application form as your agreement to the terms and conditions of the grant. Link Below.
Please send your completed application form and a copy of your 2 quotes to:
Delta Hamilton NIE Energy Woodchester House 50 Newforge Lane Belfast BT9 5NW
Then please don’t start work until you have had confirmation from NIE Energy that your application has been successful.
If your application is accepted then you will then receive a grant offer letter – households who proceed with the work without having applied and received a NIE grant offer letter will not receive a grant. There will be no exceptions to this requirement.
This new NIE Household Grant is a limited offer and is available only on a ‘first come, first served’ basis. Some installations will be profiled to raise awareness of the uptake of renewable energy in Northern Ireland.
All grant administration is managed by NIE Energy so if you require any further information about the grant please contact Delta Hamilton by emailing Delta.Hamilton@nieenergy.co.uk.
According to the Energy Saving Trust's Chief Executive Philip Sellwood, almost a third of new homes are still failing to meet energy efficiency guidelines. He told the BBC " ... the Government's 'Code for Sustainable Homes' is not being adequately enforced, giving cause for real concern. Our building regulations in the UK are among some of the toughest in Europe, but they are extremely poorly enforced as far as energy efficiency goes".
David Arendell, MD of roof ventilation specialist Klober feels the situation in respect of building air tightness gives grounds for even greater concern. He commented, "In the light of the EST's comments on energy efficiency, it is fair to assume that the level of understanding of how best to achieve air tight construction remains poor.
This is despite the fact that the phrase 'Build tight, ventilate right' has become synonymous with the strategy to achieve low energy buildings. If we don't understand how best to achieve the right balance of air tightness and controlled ventilation, we run the risk of perpetuating condensation problems within the roof space and building fabric. With every upgrade in insulation standards, so the risk increases.
Delays in consultation on Approved Documents Land G have prompted deferment in CSH 2010 until the end of the year, but the clock is undoubtedly ticking towards an ultimate target whereby all new homes achieve CSH Level 6 (effectively zero carbon). However, with house builders having lobbied consistently for tighter definition of how 'zero carbon' can be achieved, the Zero Carbon Task Group was set up.
There is some evidence to support such calls for redefinition. Research carried out in 2007 by the Richard Hodkinson Consultancy, for example, showed that 'PassivHaus' (a Europe-wide Standard with stringent air tightness requirements managed by the BRE and the Energy Saving Trust) would not actually meet CSH 3.
CSH assessment uses the Standard Assessment Procedure (SAP) test to calculate energy performance, and for a number of years there have been questions over the efficacy of the test, especially in relation to more thermally efficient buildings.
In terms of roof design, the requirement already exists for new public sector housing to meet CSH 3. The impetus towards 'zero carbon' will be reinforced when the equivalent of CSH 3 is incorporated into Building Regulations for England and Wales (some authorities indeed have already adopted this requirement). In Scotland, where many elements of the Code have already been incorporated into Building Standards, similar improvements are planned.
Of the nine categories within the CSH method of assessment, that for 'energy and C02 emissions' is by far the most significant. This is true for both the allocation of credits within each category and the final point’s allocations that result from use of weighting factors. 29 credits are available for energy and C02 emissions which, when weighted contributes 36.4% to the total available performance.
The right balance between air tightness and ventilation can certainly be struck without significant addition to building costs. Material choice however, can greatly influence a building's long-term air tightness. Sheet membrane air barriers coupled with sealants, for example, are more effective than sealants alone, counteracting the effects of buildings (particularly timber frame) drying out.
Housing designers can now benefit from Accredited Construction Details (ACDs), Enhanced Construction details (ECDs) and, in Scotland, the Scottish Ecological Design Association Guide for both warm and cold roof construction. Examples of wall/ceiling ACDs include a junction of ceiling level air barrier with masonry inner leaf and warm roof with room in the roof. Accredited detail Sheet MCI RE 02, for example, shows a warm roof detail at the eaves in a non-habitable loft using Klober Permo forte vapor permeable underlay and appropriate tapes (with an alternative pre-taped option).
For non-residential construction, air tightness is just as important, despite the absence of any CSH equivalent. Roofing materials such as zinc, for example, require airtight construction if the metal's underside is unventilated. At the recently build Abergwynfi primary school near Neath, built to achieve a BREEAM 'Excellent' rating, zinc was used on a series of circular roofs. A Klober Wallint air barrier was installed with sealing tape to meet the specified air tightness performance.
With current Building Regulation requirements stipulating air tightness of only 7m3/hr per m2 compared with CSH 3 at 3m3, techniques used to achieve it must undoubtedly change. CPD presentations and literature on the subject are to be welcomed. 'The Code for sustainable Homes and air tightness in roofs' is a CPD presentation from Klober examining how to 'build tight and ventilate right' within the realms of practical pitched roofing construction. Supported by ‘Taking control of air leakage' www.klober.co.uk/air tightness it is a welcome source of information on a subject for which information is otherwise lacking.
By David Arendell, MD of Klober