Certification | Air Tightness | Thermography




Air Tightness Testing 

Air tightness testing is a requirement of UK Building Regulations Part L. It measures the level of uncontrolled air leakage through the building fabric.

The air tightness target is established in the Design-Stage SAP calculations. The worst allowing score is 10m3/h/m2 however generally your SAP assessor will aim for a minimum of 5.00 m3/h/m2 due to the savings that can be made elsewhere int the calculation and through the heat loss in the building. There's very little point in highly insulating a home and filling it with low carbon technology yet letting all the heat leave the building through cracks and gaps in the fabric.

We offer free advice throughout the build to all of our clients and if there are problems with achieving your target on the day we have the experience and knowledge to identify air leakage paths and, where possible, get them fixed there and then to avoid costly retests. 

We use both smoke testing and thermal imaging tools to determine where leakage paths are if we can't physically feel the air flow.

Fully accredited and highly experienced
On-site results and same day certification



Free advice throughout your build


Competitive pricing
Multiple plot discounts
Flexible test appointments

Passivhaus Standards

Air tightness testing for Passivhaus dwellings varies from UK Building Regulations in numerous ways. 

  • You are required to carry out two tests at completion - one in a depressurised state and one in a pressurised state.


  • The result is measured in Air Changes per Hour (ACH) and is based on the volume of the building and not the envelope area that is used in determining Building Regulations air leakage.

  • The target is much tighter - 0.6ACH. This isn't directly comparable to Building Regulations due to the volume vs envelope area difference, however in a typical house it is generally a similar figure so over 10 times more airtight than Building Regulations Part L states.

We strongly advise carrying out testing at various stages of the build due to the stringent targets of a Passivhaus building:

      Stage 1:  Once the air barrier sealing works are completed

      Stage 2:  Once the secondary fix works are completed

      Stage 3:  At completion

Experienced Passivhaus test engineers
Tests at all build stages
Discounted thermography assessments during test visits
Full & detailed heat loss and leakage reports available