We recently completed air tightness tests on two of our new builds which are nearly finished. It is a requirement for Building Control sign-off that you provide air tightness results from a certified organisation. We use a company called PYC Systems to do the tests, but what do the tests involve and why do they matter?
Draughts were part of every day living when I grew up – unwanted cold air coming into the house around windows, through the openings, around doors, under skirting boards, through the floor – through plug sockets and light fittings! But also up chimneys and anywhere else it can find. As well as decreasing your comfort – who wants a cold draught on the back of their neck – these gaps and cracks allow warm, moist air from inside the house to escape, thereby losing heat and increasing your bills, but also allowing moisture to condense inside the building fabric and potentially causing wood to rot, for example at joist ends.
Building Regulations and Air Tightness
Building Regulations today require that all new homes meet a certain air tightness standard, reducing the unwanted infiltration of air into the home. This standard is set at 10m3/h/m2 at an internal air pressure of 50 Pa. This means, when you use a computer controlled fan to suck air into the building, you should lose no more than 10 cubic metres for every m2 of wall, every hour. This sounds like a lot doesn’t it? It is. Building to Passivhaus standards means that your upper limit will be reduced from 10 to 0.6 – almost twenty times better! According to the BRE, just reducing it to 5 can save 40% on space heating. Imagine the CO2 savings as well!
Recent results
The big builders argue against tightening up the regulations because it’s a teensy bit hard for them to even meet the current standard. However, 30,000 Passivhaus home owners know that it can be done – see below for an example of our results, which went 20% lower than the Passivhaus standard, to prove it!
We will discuss how to achieve good airtightness next.