I’ve been on a course recently to learn how to test new buildings for their Air Permeability score.
Any new build in the UK has to have an airtightness test. Building Regulations Part L demands as part of the “conservation of fuel and power” that all new homes must be tested to ensure they have an Air Permeability Score no less than 10m3/(h.m2).
10m3/(h.m2)@50 Pascals means that no more than 10 cubic metres of air must be able to pass through any square metre piece of the envelope of the inner leaf of the building, per hour, at 50 Pascals (which is a light breeze blowing against the home).
Lower Air Permeability Test Score
A lower Air Permeability test score means your home is airtight, and therefore it’s easier for it to conserve the heat you create (ie, the hot air from your radiators doesn’t just leak through the brickwork).
A higher Air Permeability test score means there are holes in the fabric of your home that air can easily escape to the outside. This will make it difficult to heat your home cheaply and effectively. It’ll be cold and draughty and expensive to live in.
Air Permeability Test Score of 5m3/(h.m2)@50Pa or lower
In a new build your Air Permeability test score that the building has to achieve will be set as part of your SAP compliance document. It could be as low as 2 or 3m3/(h.m2)@50Pa, but this will be very hard to achieve. A fairer score, and one that will be nicer to live in(!), is anything lower than 5m3/(h.m2)@50Pa.
But keep in mind, as you make your home more airtight you increase the risk of moisture and stale air problems. You must consider some kind of background mechanical ventilation system (such as an MVHR) in order to remove the humid air that washing, cooking and breathing generates. Black Mould will form in houses that are airtight and don’t have adequate ventilation.
Failing your Air Permeability test
If I do pass my evaluation and I come to your home to do your airtightness testing, the procedure is
- I put a blower door in your front or back door.
- We close all windows and doors, and we seal up all ventilation points (chimneys, extractor fans, etc).
- I run the fan and pressurise or depressurise the building to 50 Pascals of pressure (if we depressurise the building you can walk around and “feel” the leaks).
- I take airflow measurements across a range of pressure points, and align it with static internal and external pressures.
- I calculate your Air Permeability test score.
I really hope you pass the AP test, but if you don’t you shouldn’t get upset. Failing the Air Permeability test score means you’re in a building that will be cold, draughty and expensive to heat in the future. You don’t want that.
The fail will still be logged with ATTMA, but we can walk around the building whilst the building is depressurised and perform a forensic airtightness test, where we will ascertain where the leaks are and how to fix them.
How to know if your builder took short cuts
Testing for airtightness is a relatively new procedure but it’s one of the best measures we can take to ensure new homes are built correctly and with the conservation of fuel and power at front of mind. The Air Permeability test score is also probably the best way to work out whether your developer/builder/contractor/architect has actually done a good job. It is an honest test of your building – you can’t lie your way out of it, and you can’t hide from it.
Finally, here’s a short video on testing air permeability testing in the UK: