As far as we know, the Denby Dale house will be the first Passivhaus in the UK built using cavity wall construction. European construction is typically solid masonry with external insulation and render or timber frame, and so Passivhaus buildings tend to use one of these two methods. But there are many ways of crossing a river, and we've decided to use cavity wall at Denby Dale, for three main reasons.
June 1, 2009, by Bill Butcher
Published by Building
First, cavity walls contribute to a high thermal mass within the insulated building envelope – allowing a more even living environment, in terms of both acoustics and temperature. Through use of concrete blocks and concrete ground-floor slab within the thermal envelope, the house will have a greater thermal mass, which will act as a heat store, storing heat gained from passive solar gains.
Second, cavity wall construction is the method that we at Green Building Company are most familiar with (we used it to build the Longwood low-energy house in the 1990s). We wanted to build a Passivhaus using British construction techniques, with, as far as possible, materials you could find in any local builder's yard.
Third, West Yorkshire planning rules require natural stone facing on the exterior of new buildings and so ruled out the option of block-built construction with rendered finishes.
The potential downside of cavity wall construction is that it relies on wet plaster to be the airtightness barrier on walls and junctions with doors, windows, floors and roof, whereas timber frame construction can be lined with vapour barriers and airtightness tapes etc, so our cavity wall Passivhaus will demand greater attention to airtightness detail.
The site had to be levelled This week I've been finalising choices for some materials on the build. We need to keep space heating needs at or below the magic figure of 15kWh/m2/annum – the prerequisite for Passivhaus certification. Modelling different materials in the Passivhaus planning package (PHPP) can have dramatic effects on that figure, and this week the figure has ranged between 19-14kWh/m2/annum, depending on which type of wall insulation and window configurations we have inputted.