Passivhaus vs Code for Sustainable Homes - 17

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.