Passive house architects

An outstanding issue: The Performance Gap

An outstanding issue: The Performance Gap

I read that the construction industry had experimented with adding insulation to new buildings and that energy consumption had failed to reduce. This offended me – it was counter to the basic laws of physics… So I made it my mission to find out what [they were doing wrong] and to establish what was needed to do it right.

Thermal Mass - Understanding its benefits

Thermal Mass - Understanding its benefits

Thermal mass 'Thermal mass' describes a material's capacity to absorb, store and release heat. For example water and concrete have a high capacity to store heat and are referred to as 'high thermal mass' materials. Insulation foam, by contrast, has very little heat storage capacity and is referred to as having 'low thermal mass'.

The embodiment of low carbon

Now nearing completion, the University of East Anglia's (UEA) most recent development, The Enterprise Centre, is on course to become an exemplar low-embodied carbon buildinq, pushing the boundaries for sustainable architecture.

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

Passivhaus vs Code for Sustainable Homes

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.