An air pressure test on a building is a way to measure the air permeability of the building, or put simply, the rate at which it leaks air, and therefore heat. The less heat a building loses, the less energy is required to heat it.
To perform an air pressure test, the following steps are carried out:
- All “designed” ventilation (the openings in the building fabric that are designed to be there, e.g. windows, doors, extract fans, etc) is sealed;
- A fan in an air tight lining is fitted into the main doorway of the property;
- The fan is powered up until it maintains a constant excess pressure of 50 Pascals;
- The rate at which the fan is then working defines the air permeability of the building, which is measured in cubic metres per hour. A minimum score of 10 (the lower the air permeability the better) is required under current building regulations for new build houses.
All properties being retrofitted are having air pressure tests carried out before the retrofit work commences, and then again afterwards to see what improvement has been made.
Our properties were air pressure tested today and actually scored well for 1940’s houses; one achieved a score of 9.36 (slightly better than current new build standards) and the other 10.6.
Below is a video of the air tightness testing on one of the houses.
Our target for the retrofit is to get those scores down to at least 5. Our homes at HHP scored an average of 1 when tested just after they were built. With air permeability rates this low, you need to mechanically ventilate the building, but this can be combined with a heat exchange unit so that much of the heat in the stale air you are extracting can be used to pre-heat the cooler fresh air you are bringing in. We plan to incorporate a mechanical ventilation with heat recovery unit in the houses as a part of the retrofit, but more on that another day …