Frequently Asked Questions

Air Tightness Testing can be a mysterious test to those not in know. Below, we have answered some frequently asked questions from Building Control and Approved Inspectors across the country.

What exactly is Air Tightness Testing? 

Air Tightness Testing is the process of establishing the amount of air leaking from inside (lovely heated air) leaking to outside (waste of money, CO2). The test method itself is actually pretty straightforward. We install a fan into a doorway of the building and blow air through the fan into the property to create a ‘pressure’ inside the house (much like blowing up a balloon (we don’t damage the property though!). Because we know how much air is going through the fan, we know how much air is escaping and therefore we have a leakage rate.

Because bigger buildings could have a bigger leakage rate than smaller buildings, but not leak as much air, we divide the leakage rate we have found by the size of the building. This gives us our final result, expressed as “m3.h-1.m-2@50Pa”. It’s a bit of a mouthful, so here it is broken down:

  • m3.h-1 (metres cubed per hour)
  • .m-2 (per metre squared of external envelope)
  • @50Pa (at 50 Pascals, which is the reference pressure difference we create with our fan).

How do I know whether a test has passed or failed? 

Air tightness testers do not actually provide a pass or fail result. Air testers simply measure the performance of the building and report back. The target air leakage figure comes from the SAP or SBEM calculation (the energy model of the building). Because we are measuring how leaky a building is, the lower the number is, the better the result is.

How do I know whether a plot is ready for testing?

The ATTMA has created guidance on when a plot should be tested. Technical Information Leaflet 002 – Are you ready to test gives guidance.

By making our housing stock very air tight, aren’t we causing sickness in both buildings and humans? 

The short answer is no, we are not. the not so short answer is that air tightness has no effect on the air quality of a building, when the building is properly ventilated. Lack of enforcement of ventilation regulation means houses are being allowed to become very air tight but the ventilation is not being checked. Study’s have shown that the ventilation in new-build properties is often far less than designed.

Should I accept a report from a tester that is not in a competent persons scheme? 

Building Control and Approved Inspectors can accept certificate from testers that are not in a competent persons scheme. ATTMA and iATS (the two authorised competent persons schemes in the UK) are both voluntary schemes. If a tester is not in a competent persons scheme, The Building Control Officer or Approved Inspector must be provided with evidence that the tester is competent. This shall include as a minimum:

  • Evidence that the equipment is UKAS calibrated within the last 12 months
  • A full test report that complies with Section 3 of ATTMA TSL1, ATTMA TSL2 or BS EN 13829:2001 for Scotland.
  • Evidence that the testing company complies with the National Occupational Standards
    • This will typically be a third party audit by an accredited company

In reality, this is time consuming and pushes the risk of a non-compliant and potentially fraudulent test on to the Building Control Officer / Approved Inspector. In the ATTMA scheme, competence is simply proved by showing building control an official ATTMA Lodgement Certificate. If the tester is not up to date with audits and competence requirements, they cannot lodge their test and receive a certificate.

Are BINDT certificates still valid? 

No, BINDT closed their testing scheme on 31st January 2014 and continued to allow memberships to run out throughout 2015.

The use of the BINDT logo is also forbidden and any uses of the logo should be reported to BINDT.

I think have been provided with a certificate that I do not believe is genuine?

If you have been provided with test evidence that you have reason to believe is not technically correct, you must at once contact the manager of the scheme that the tester is in. If the tester is not in a scheme, the evidence shall be rejected unless they can demonstrate compliance.

The ATTMA are proud to offer a free report checking service. Reports can be submitted at where we can advise if the report is completely acceptable or we will highlight the areas of concern.

I think have been provided with a certificate that has unacceptable deviations?

Deviations from tests are common. It is acceptable to temporarily seal an item if it will be fixed at a later date. If an item has been temporarily sealed that will not be put right at a later date (for example a boiler cupboard door, skirting boards, bath panels), the test must immediately be rejected and reported to the manager of the competent persons scheme the tester belongs to. If the tester is not in a scheme, the evidence shall be rejected unless they can demonstrate compliance, usually by repeating the test at a later date.

ATTMA have provided a document to show what is and is not acceptable to temporarily seal. This can be viewed at: TIL001 – Temporary Sealing in Dwellings.