What does air tightness testing involve?

The objective is to measure the volume of conditioned air escaping through the building envelope via uncontrolled ventilation at an induced pressure difference of 50Pa.

The following basic steps are typical:

  • Check site preparation / Prepare site – including temporary sealing
  • Calculate the envelope. This is prefered to be calculated prior to site visit
  • Explain the process to relevant staff and sub-contractors working on or near the building
  • Take environmental condition measurements – wind speed, temperatures, barometric pressures
  • Install fan into door / opening
  • Connect monitoring equipment
  • Check the static pressure before test
  • Take multiple pressure difference readings and record fan flow rate(s) – allowing sufficient time for the pressure readings to stabilise
  • Check the static pressure after the test
  • Input the data readings into software – check that readings are at the right standard for test
  • Calculation of the results from test pass or fail
  • If the building fails, we pinpoint key leakage paths and help client / staff on remedial work
  • Then rerun test stage again
  • Note results pass or fail / discuss results with client
  • Disconnect measurement equipment
  • Remove the fan

What test evidence is required?

A test certificate from a test engineer that is registered with the British Institute of Non-destructive Testing (BINDT).

The test certificate should provide information of the building eg. location, type and size (the envelope area is an important component in calculating the air permeability and must be accurate) plus the design air permeability as well as the actual result. Building Control should satisfy themselves that the building tested was representative of the actual performance.

The test certificate should refer to BINDT registration and membership number of tester.

When will I get the results?

An indicative result is available immediately. Certificates can be issued on the same day, when required.

Reports with certificates are typically sent within 2 working days. Report to local authourites within 3 days.

What happens if the building fails?

At A1 Air Testing we will provide all relevant information in order to achieve a pass.

In the event of a failure we will carry out small remedial works or assist client as much as possible and aim to retest on the same day. Smoke can be used to identify where air is moving when the building is being tested.

Depressurise method is used to identify air leakage paths in combination with smoke to the building. In the vast majority of cases our method is sufficient to identify the most significant air leakage paths. Where problems are larger and cannot be addressed on the day, the building may need to be re-tested at a later date.

How is air tightness calculated?

Air permeability is the calculation of the pressure difference between the inside and outside of the building and air flow rate through the fan to produce that pressure difference. This is averaged out over the envelope area. The result takes account of environmental conditions.

The final air permeability at 50Pa is based on a logarithmic graph of pressure difference and flow rate, the graph should:
- Have at least 8 points 15 in windy conditions.
- The highest figure should be at least 35Pa but preferably would be in excess of 50Pa and ideally higher than 60Pa
- The lowest should be greater than 10Pa or no lower than 5 times the ‘static pressure’ (the pressure difference between inside and outside without the fan – which in itself MUST be less than 5Pa often raised by excess wind. - The correlation of the graph should be at least 98% -100%
- The gradient of the graph (n) should be between 0.5 and 1.0

How long does an air tightness test take?

Depending on:
The size/complexity of the building which affects the pre-test checks,and temporary sealing ie chimneys etc
The access to the site which affects set up times
Cooling down of property in winter time. We recommend heating off prior to test

Assuming key factors are satisfactory, test normally takes 1 - 2 hours