Innovation – Passivhaus
Welsh Government targets for sustainable construction make it imperative to establish a design standard for social housing that is low cost, energy efficient, and keeps household energy bills to a minimum. United Welsh commissioned the three-bed Larch House as a prototype social home to test the effectiveness of the Passivhaus concept in meeting these requirements.
Passivhaus is a demanding construction standard for extremely low energy buildings that do not compromise on comfort. Passivhaus design seeks to eliminate as far as possible the need for space heating and cooling by keeping heat loss to a minimum. This requires much higher standards of insulation and airtightness, than are normal in the UK.
In fact, the completed Larch House exceeded expectations by reaching the zero carbon Passivhaus standard – a first in the UK. This was achieved by challenging normal housing conventions through a plethora of new solutions. The judges were highly impressed and commented that the UK construction industry has a huge amount to learn from Passivhaus. The implications of it, they said, are potentially ground-breaking.
The Larch House initiative was a joint partnership between United Welsh, BRE (Wales), Blaenau Gwent County Borough Council, and the Welsh Government. In 2009 Bere Architects won the competition to design a low-cost house that would showcase the Passivhaus concept and incorporate innovative measures for energy efficiency.
The house was built between March and July 2010 on the site of the former steelworks at Ebbw Vale. The south-facing building is timber-framed, with triple-glazed windows, highly insulated closed-panel timber framing, draught-free construction, heat recovery ventilation system and photovoltaic panels all contributing to its energy efficiency.
Environmentally friendly materials were used, including untreated softwood, wood fibre insulation, Welsh-grown thermally-modified larch cladding, ecological paints and low energy LED lighting. Much of the material was locally sourced, and local labour was employed.
Although the Passivhaus is a German concept it was always the intention of the projects group to learn from the manufacture of these products and look to ‘skill-up’ Welsh and UK companies to meet future requirements. Holbrook Timber Frame – the timber frame fabric subcontractor, based in Bridgend – succeeded brilliantly in producing a building fabric capable of delivering the stringent Passivhaus standard of insulation and airtightness. This involved making huge improvements to their existing processes as well as learning a new manufacturing technique for producing tailored bespoke panels.
The project also acted as a training ground for Welsh companies to learn how to design and produce Passivhaus-certified windows.
The brief required the Larch House to achieve code 5 of the code for Sustainable Homes but in the event the completed building exceeded expectations with a code 6 zero carbon rating, making it the UK’s first Passivhaus. It generates as much energy from the sun in the summer as it uses for the whole year. Income from the feed-in tariff over expenditure is estimated at over £900 a year.
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 is a triumphant result for Wales’s first attempt at a Passivhaus. Equally important, however, is the building’s performance when occupied and over time. The house is being carefully monitored to analyse its actual energy consumption, which will continue for the first two years of occupancy.
This matters because a key deterrent to constructing low energy buildings is the relatively high build cost. If this can be offset by reduced energy bills throughout the life of the building, the arguments in favour of investing in low energy design become more compelling. If it can be shown that a Passivhaus will have lower whole life costs compared to a traditionally built new building, homes like the Larch House could truly prove a cost-effective solution to reducing carbon emissions.
What is certain is that lessons learned from the design and construction of the house will be taken forward into larger social housing schemes being developed by United Welsh – and, as the judges observed, probably far beyond.
Greg England, United Welsh Housing Association
“Larch House is a testament to successful partnership working. This innovative house is a real statement from the social housing sector in Wales. It is important that we continue to build houses that incorporate sustainable features both in the finished product and in the building process. 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.”