Everything you need to know about air tightness testing, Part L regulations, and the testing process. Can't find your answer? Contact our team.
What is air leakage?
Air leakage is the uncontrolled movement of air through gaps, cracks, and defects in the building fabric. It differs from ventilation — which is the deliberate, controlled flow of air through purpose-designed ventilators installed for the comfort and safety of occupants. Air leakage cannot be regulated; it is an unintentional opening in the building envelope.
Why is air tightness important?
Air tightness is a key indicator of a building's energy efficiency and overall performance. Under Part L of the Building Regulations, air testing is a mandatory requirement for all new builds in England and Wales. Achieving adequate air tightness reduces heat loss, lowers energy bills, minimises carbon emissions, and creates a more comfortable indoor environment.
Is air tightness testing mandatory?
Yes. Under the Part L Building Regulations, air tightness testing is a legal requirement for all new dwellings and qualifying new commercial buildings. The regulations are enforced at the point of building control sign-off and failure to test can delay your completion certificate.
Which types of buildings require air testing?
Air testing is required for all new dwellings, all new non-domestic buildings, and large extensions to non-domestic buildings. Buildings undergoing material change of use may also require testing. Contact our team or your building control officer for project-specific guidance.
How much does an air tightness test cost?
The cost depends on the size, type, and completion stage of the property. Commissioning at the right stage minimises the risk of failure and avoids re-test costs. Buildings achieving a strong air tightness result can also benefit from improved sale values and enhanced energy ratings. Contact us for a tailored quote.
What happens if an air tightness test fails?
If the result doesn't meet the required air permeability standard, the defective areas must be identified, remediated, and re-tested. At Air & Sound Testing, our engineers identify the source of leakage at no additional charge — and if the client's workforce can remediate on-site during the same visit, we conduct a free re-test.
Do extensions require air tightness testing?
Extensions with a total useful floor area exceeding 1,000 m² may require testing subject to technical and economic feasibility. For domestic extensions below this threshold, testing is not typically required — though good air tightness practice is always encouraged as the regulatory requirements continue to evolve.
When should air tightness testing take place?
Testing is typically carried out at the latter stages of construction, once the building is substantially complete and all services penetrations through the envelope have been sealed. Testing too early increases the risk of failure. We recommend discussing the optimal testing stage with our team as early as possible in the project programme.
