THE TEST
The basics of the air pressure test [APT] system of measuring the air
permeability of a property are, at a high level, as simple as connecting
a large fan to an external door in order to draw air into the property.
When it has reached a certain level of pressure this is, then, reduced
at the same rate it was increased. The volume of air loss is measured
and compared to the value stated in the appropriate regulations.
Below we have supplied more specific detail.
Envelope Area
This is calculated as the area of the external walls, roof and footprint of the building. The roof area is the area below the roof, if this is non dwelling. Note this is for detached property. This should be detailed in the Carbon Emission Rating [CER] Calculation but should be checked prior to testing. Once the area to be tested has been identified it is necessary to identify the Target Emission Rate [TER]. For residential dwellings this is 10 m3 (h.m2) at 50 Pa.The APT value will defined by the designer in the CER evaluation. These factors determine the size or number of fans to be used.
On arrival on site it is necessary to check that the building and environmental conditions are ready for the test to go ahead. The operative completes a pre test checklist confirming that all internal seals, temporary and permanent, are in place and that the building is ready for testing. He measures the wind speed, a reading equivalent to 3-4 on the Beaufort Scale is required, and pressure and temperatures inside and outside the building.
Once the building is ready he confirms that no one will enter or leave the building during the test and runs the fan pressurising the building. During this phase he takes readings and monitors the process. For test verification purposes the readings should be the same on pressure increase as on pressure decrease.
The technician then does a preliminary analysis of the results and determines if the building is likely, on analysis to pass or fail the test.
He then dismantles the equipment, returns the property to its pre test state and discusses the results with a client representative. If the test passes he will prepare his report and issue the appropriate certificate.
In the case of a near fail he conducts a visual inspection, using leak detection equipment, in an attempt to identify the cause of the near fail. If this is easily locatable and easily repairable he arranges for this to be done and undertakes a re-test. All these actions are recorded and included within the report.
A building can have its pressure lowered by, reversing the fans, drawing the air from inside the property outward. Smoke generators are then used on the internal surfaces, joints and likely points of egress. The smoke should flow away from the point of the leak.
It is also possible to seal off different areas of the building and test these smaller areas. This narrows down the likely areas where leakage is occurring.
Should the fail differential be more significant he conducts a visual inspection, prepares a report into the probable causes of the negative result and discusses remedial action with the client or their representative.