Period Feature v The PassivHaus

Most old homes in the UK have large brick chimney breasts running from top to bottom. These used to carry smoke up and out of the house when people burnt coal to stay warm.

As part of the build, we are taking all of our chimney breasts out. We know this is a little controversial and no doubt Kevin McLoud would be tearing his hair out at the loss of period features, but we have to do it for a couple of reasons:

1. To help us achieve the level of airtightness required for a passivhaus; and

2. To recover some of the floor space lost to internal insulation.

Airtightness is a central design component of the passivhaus – to be passivhaus certified, a building must achieve airtightness of less than 0.6 air changes per hour at 50 Pa (i.e. when pressurised). This is practically impossible when there are large flues running from the ground to the top floor. The flues will soon be filled in.

Space - The other reason for removing the chimney breasts is to recoup some of the space lost to the internal wall insulation, which will eat up about 10m2 of internal floor space. Taking the chimney breasts out recovers 4m2; a net internal floor space loss of 6m2, which we don’t think is all that much given how snug it is going to make our house.

There is not only a liveable space point here, but also one of house value. For quite a few of the 7 million solid brick wall houses in the UK, external insulation will not be an option; meaning they will have to be insulated internally. It will be harder to persuade the owners of these houses to insulate internally if doing so means the value of their houses falls significantly. The good news is that insulation technology is improving all the time, so hopefully there will soon be an affordable and practical product for achieving very low U-values…

Conservation rules (our old friend) dictates that the original chimneys at the top of the house must remain in place despite there being no working fires in the house. This means that we have to build a steel frame to support the (enormous and very heavy) chimney stack. One of the photos above shows it being propped up whilst the steel frame is put in place.

Whilst I recognise the aesthetic qualities of chimneys, leaving them in place has another disadvantage – they will cast shade over the solar PV panels that are to be positioned on the flat roof, thereby reducing their efficiency.

One final thing to note about removing chimney breasts - it’s incredibly DIRTY work!