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The UK’s first zero-carbon Passivhaus

Housing Associations leading the way - Sunday Mirror report

How Green Is their valley - The Guardian Online

At a showcase exhibition at the National Eisteddfod for Wales, United Welsh and its partners have launched the UK’s first zero-carbon Passivhaus.

View press release                      View the Video

The house is a one-off, incorporating and integrating many design features for the very first time in the UK. The initiative is a joint partnership between United Welsh, BRE, Blaenau Gwent Council, and the Welsh Government.

As part of the National Eisteddfod festival 2010 United Welsh was invited to partner in the running of a prestigious construction competition to build a house on the Eisteddfod site to showcase the ‘Passivhaus’ concept. After a large response to the competition from international designers and builders, the partners identified and chose those who could meet the high standards needed to deliver the project successfully. One of these standards was to incorporate as much locally sourced material, products and know-how as possible.

The successful designers were Bere architects a practice that advocates the principles of sustainable development. Pendragon Design and Build were awarded the build contract - a Welsh company based in Cwmbran tackling Passivhaus for the first time.

The three bed property, called the ‘Larch House’ after its Pembrokeshire Larch cladding, has been designed to meet the Passivhaus concept. It is 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. Large south-facing windows, closed-panel timber framing to minimise draught, high insulation, and photovoltaic panels all add to the zero-carbon footprint of the property.

Gareth Davies, Head of Development at United Welsh said: “We are absolutely delighted with what has been achieved. This house is a real statement from the social housing sector in Wales. It uses cutting edge technology, the very latest in building material & techniques and some clever thinking to create a home that’s super efficient, low cost to run and will be a pleasure to live in now and in the future.

“It’s important that we continue to build houses that incorporate sustainable features both in the finished product and in the building process. We are determined to get the balance right between incorporating greener methods of building, offering benefits to tenants through things such as lower energy bills, and providing a service that can be delivered for years to come.” 

This project has achieved outstanding levels of air-tightness, and surpasses Building Regulations by some margin. It achieves the Passivhaus standard of less than or equal to 0.6 air changes per hour at 50 Pascals.  In fact, it is probably the best result so far for a UK pressurised air test for an above-ground, detached house. On decompression at 50 pascals the result was 0.17 air changes per hour, but on average 0.197 air changes per hour was the final result as measured and calculated by Paul Jennings, probably the UK’s most respected air testing specialist. 

This result is over three times better than the minimum required by the Passivhaus Institute and right up there with the very best German results. This is all the more remarkable as this is the first time this Welsh partnership has ever attempted to achieve the Passivhaus standard.

The key outcomes other than to achieve Passivhaus standard was to learn lessons from the design and construction of the 3 bed prototype and take forward onto larger social housing schemes. Progress has already been made with the window element. A certifiable Welsh manufactured Passivhaus compliant window has been installed on a 2 bed property on the same site. It has been supplied by Custom Precision Joinery – a Welsh based company from Flintshire. Working with BRE and Wood Knowledge Wales, they are the first UK window supplier to gain Passivhaus certification.

The whole project will be carefully monitored with tenants moving in shortly. The design will be refined to eventually achieve an economically viable product that can be developed at scale, to an agreed standard, using a local supply chain.

Basic Principles

A dwelling which achieves the PassivHaus standard typically includes:

  • Very good levels of insulation
  • Incorporate the use of solar energy
  • Excellent level of air tightness
  • Good indoor air quality 
  • Efficient heat recovery, ‘passive’ use and heating of air
  • Low levels of energy demand to heat and run property
  • Energy-efficient glazing


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