Air Pressure Testing

Updated: 21st March 2016

Since 2006 it has been mandatory under Part L of the building regulations to carry out an air pressure test on new builds. The purpose of this legislation is to conserve fuel and power, by minimising air leakage and thus heat generated from whichever source the building is using. With draughty buildings radiators are pouring heat to outside air, creating a need for more heat to be generated, thus damaging the environment. The service life of a building is potentially the most harmful part of a buildings life to the environment, so it is important that buildings are designed to minimise service life impact. Although all buildings need ventilation, what they don’t need is uncontrolled air leakage from unknown areas.

The building regulations stipulate that a SAP calculation is submitted at the design stage, which is an energy efficiency calculation based on design values. Input into this calculation are the design thermal values of walls, windows, floors, roofs etc…; the designed heat source and predicted efficiency of heating appliances, renewable energy input, and the air leakage design value (amongst other considerations). This gives you a predicted energy efficiency result. The building is then constructed, and an as built SAP calculation is carried out inputting the actual values. The Energy Performance Certificates (EPC), which are provided for all houses nowadays, are based on the result. And the air leakage test must be carried out on the new build to establish the value for the calculation.

The test is carried out be specialists, where they will close all windows and doors, seal all vents and extractor ducts so that all known ventilation paths are closed off. They then open an external door and seal it with a large extractor fan in the centre of the door seal. They extract the air from the house and measure the pressure difference from outside to inside, and time how long it takes for the pressures to equalize and thus the amount of unknown leakage in the house. A result of “0” means there is no leakage. Newer houses typically have results in the region of 5, and older houses nearer 15. To establish where the leaks are coming from the fan can be reversed, pressurizing the house, and smoke is used near areas where there might be suspected leakage (like pipes exiting walls, window sills etc…), to show the smoke exiting the leak.

To reduce leakage caulk can be used around windows and door frames, foam can be sprayed around pipes where they exit walls, when dabbing plasterboard onto masonry, the top dab can be a solid line of glue, preventing air travelling behind the plasterboard into the loft, skirting boards can be caulked. More labour intensive things to remedy are gaps between exposed floor boards and sash window leaks. Both are attractive architectural features but inherently leaky.  

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