Air Pressure Tests

airPressureTestLegal Requirements

  • Although it is not mandatory to undertake an Air Pressure Test (APT) on a building, it is often neccessary to do so as to comply with Part L of the Building Regulations.
  • The results from an APT have a large impact upon the results of Energy Performance Calculations for New Dwellings.
  • for a new dwelling it is reccommended to set a target APT value of 5 m3/h.m2
  • There are a few exceptions
    • On small development sites of no more than 2 dwellings a default air pressure test value of 15m3/h.m2 can be used thus avoiding the need for an APT. However this will often result in non-compliance with Part L1A
    • On larger developments, dwellings which are self similar can be grouped and a pressure test done on only one member of the group. However you must add an extra 2m3/hm2 to the measured value when applying it to another member of the group that was not measured.

The Air Pressure Test

The person undertaking the Air Pressure Test requires a 'target' value to aim at before they start the test. This target value is taken from the SAP calculation and is typically set at 10m3/hm2, however if there are problems in gaining Part L compliance then it might be neccessary to reduce it as low as 3m3/hm2. Values below this are quite difficult to achieve.

To carry out an APT

  • A 'blower door system' will be erected in an appropriate external door; this system holds the fan units and acts as a seal around the opening of the door frame.
  • Any 'designed' leakage points in the dwelling (such as trickle vents, letter boxes and extract fans) are then sealed to prevent escape of air.
  • The dwelling will then either be pressurised or depressurised (by the use of the fans).
  • The pressure difference between inside and outside the dwelling and the amount of air passing through the fan, needed to maintain the specific pressures, will be recorded. This process is carried out at a number of different pressures and can take about 30 minutes.
  • Using the pressure differences, the flow rates and the envelope area, the dwelling's air permeability is calculated.
  • A final report is produced showing all the details and data from the APT.


Pricing depends upon the complexity and location of the building. If you would like more information, advice or a quotation, then please call

Richard Owen on 01485 544757 or click here for contact information  >>>    Contact Us