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The Deerings, Harpenden, UK. Design by Gresford Architects, 2017.

RAISING STANDARDS

As the 1,000th Passivhaus unit in the UK awaits certification Timber Construction explores what it means to build to the standard.

The Passivhaus Standard was developed in Germany over 25 years ago – the brainchild of professors Bo Adamson and Wolfgang Feist.

Physicist Feist had been researching low energy  buildings and was perplexed as to why they weren’t performing as well as predicted. He went on to build the world’s first Passivhaus home in Darmstadt, Germany, which was completed in 1991.

Since then over 65,000 buildings (both residential and commercial) worldwide have been designed, built and tested to the international energy standard, undergoing a rigorous quality assurance process.

There is no set formula to building to the Passivhaus Standard which does not define a particular construction method or material, but a key objective is to drastically reduce a building’s  operational energy while prioritising the comfort of  occupants. Buildings must achieve minimal thermal bridges and have an airtight building fabric to minimise heat loss.

Passivhaus buildings offer a stable and comfortable environment all year round, regardless of the weather, with heat loss reduced by up to 90% meaning that they require very little heating, while the constant purified air reduces condensation and mould.

Y Foel Passivhaus in Powys, Wales, became the first property in the UK to be certified to the Passivhaus Standard in August 2009.

Since then over 800 units have been certified and there have been several large-scale Passivhaus developments including a 51-home affordable residential scheme in Rainham, Essex, and Carrowbreck Meadow, a development of 14 Passivhaus homes in Norwich.

All 68 of the timber frame homes at the Saffron Acres development are Passivhaus certified – a condition imposed by Leicester City Council when it sold the land to Saffron Lane Neighbourhood Council for £1.

Commercial buildings constructed to the standard include the University of Leicester’s £42 million Centre for Medicine, which is the largest non-domestic Passivhaus building in the UK, and one of the largest in Europe, the Enterprise Centre which is part of the Norwich Research Park and Herefordshire Archive and Records Centre.

But there are just 30 commercial Passivhaus buildings in the UK and Passivhaus homes account for less than 1% of domestic dwellings.

There is a perception that Passivhaus buildings are “too expensive, high risk and very challenging” said a spokesperson for the Passivhaus Trust, an independent, non-profit organisation that provides leadership in the UK for the adoption of the Passivhaus Standard and methodology.

The UK affiliate of the Passivhaus Institute in Germany, it was formed in 2010. It says that builders and private clients have been quicker to adopt Passivhaus because of the benefits to occupants and lower whole life costs but these don’t always align with the priorities of volume builders.

However, there has been an increase in the number of developers and mainstream contractors interested in adopting Passivhaus as a unique selling point.

“This is encouraging as it means the value and quality of the standard is finally being recognised,” said the spokesman, adding that people’s perceptions about Passivhaus will change as more homes are built and experiences and knowledge are shared.

“We need to continually provide education in demystifying Passivhaus for the mainstream construction industry and are lucky that the UK and international Passivhaus community are very happy to share knowledge and information.”

There can be an additional capital cost for Passivhaus homes, says the Trust if you keep everything else (design standards) the same but if you are willing to adjust the design to be more efficient for Passivhaus then it can be possible to achieve the standard at no extra cost.

It is also worth taking into account the fact that a Passivhaus building offers far superior build quality, energy performance and internal comfort than a similar scheme built to typical building regulations., not to mention the lower whole life costs of the building.

Additional capital costs have decreased significantly in the UK over the last few years due to better awareness of the standard, increased demand, and an ever-improving supply chain and as more homes are built to the standard it will become even more cost effective to meet.

“We need to nurture more Passivhaus designers and tradespersons to effectively implement the required skills to build to this level,” said the Passivhaus Trust spokesman. “We can all help by asking for more. Homeowners to renters should all be enquiring where and when they can live in one, which helps to influence the market.”

While there is still some way to go before Passivhaus becomes part of the mainstream there are some areas within the UK, such as Exeter and Norwich which are trailblazing the adoption of the standards and many localised plans are beginning to ask for higher levels of energy efficiency for buildings.

There are also many examples from around the world that the UK can learn from. For example, in the Brussels region Passivhaus is mandated for all new construction and major retrofits, while new buildings in Vancouver are to have zero operational greenhouse gas emissions by 2030.

The Passivhaus Trust believes that a secure commitment to meeting global environmental targets would be a huge start from the UK Government along with upgrading Building Regulations to Passivhaus levels of criteria for energy efficiency & stating a kWh/m2/yr target.

Main pic – The Deerings, a new-build certified passivhaus in Harpenden, Hertfordshire. Pic credit – Quinlin Lake ©

CASE STUDY: THE DEERINGS

  • Client: Private individual
  • Architect: Gresford Architects
  • Main contractor: MBC Timber Frame
  • Structural engineer: Tanner Structural Design Ltd
  • M&E consultant: Crofton Design Ltd
  • Project manager: Trunk Low Energy Building Ltd
  • Ventilation design: Green Building Store

Pic credit – Quinlin Lake ©

Kebony was chosen for the cladding at Avondale Park Primary School, North Kensington, London, which was recently extended and refurbished by ECD Architects.

The five-bedroom home is a sympathetic response to its urban setting and sits comfortably alongside its more traditional neighbouring properties.

It was built from a super-insulated timber frame, which was constructed offsite by MBC Timber Frame and was erected on a passive slab from MBC, which also supplied insulation and airtight membrane.

The frame was built in three weeks, significantly speeding up the overall programme, and minimising wastage and disturbance to neighbours. Recycled paper insulation and external timber cladding were chosen to reduce the carbon footprint of the building, minimising the use of concrete and steel to less than 10% of the total volume.

A heat exchange system provides constant background ventilation, removing stale air and drawing in fresh air, so the house always has a fresh, ventilated feel, while maintaining its warmth.

A specialist Passivhaus certified woodburner was occasionally used and although a back-up gas boiler was supplied it was never turned on, as even on the coldest days, without the heating, the house maintained its ambient temperature of around 21 degrees.

The Deerings, which was completed in October 2017, was a joint project by Nicolas Tye Architects, who prepared initial plans and secured planning consent for the project, and Passivhaus experts Gresford Architects, who developed the design through the detailed design and construction phases.

SUSTAINABILITY DATA:

  • Heating demand kWh/(m²a): 12.0 (maximum for PH Certification 15.0)
  • Frequency of overheating (> 25 °C): 2%
  • Pressurisation test result n5 1/h: 0.5 (maximum for PH Certification 0.6)
  • Non-renewable Primary Energy Demand (PE) kWh/(m²a): 45 (maximum for PH
  • Certification 120)
  • Primary Energy Renewable Demand (PER) kWh/(m²a): 37
  • Generation of renewable energy (in relation to projected building footprint area) kWh/
  • (m²a): 25
  • Predicted annual energy use (regulated and unregulated)/CO2 consumption (including
  • contribution from low carbon and renewable technology): 9.9 KgCO2/m2/y
  • Contribution of renewable technology: 82.2 %

 

 

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