Quality & Inspections · Mandatory · Completion
Air Tightness Test Record
A record of building air permeability testing required under Part L of the Building Regulations.
Last reviewed: 29 March 2026 — This guide reflects UK law as of this date. Building Regs Part L / SAP remains current with no amendments enacted as of 29 March 2026. Next scheduled review: 29 March 2027.
| Legal basis | Building Regulations Part L + SAP (Standard Assessment Procedure) + ATTMA TS1 (Air Tightness Testing and Measurement Association Technical Standard 1) |
| Why test | Quantifies air permeability of the building envelope — if worse than the SAP assumption, Part L compliance may be affected and the building may not receive an EPC |
| Test method | Blower door pressurisation at 50 Pa, result expressed in m³/hr/m² of envelope area |
| England targets | Maximum 8 m³/hr/m² at 50 Pa; design target typically ≤5 m³/hr/m²; Passivhaus standard ≤0.6 ach at 50 Pa |
| Accredited tester | Must be an ATTMA member or equivalent accredited testing organisation |
| Before test | Seal all intentional openings (trickle vents, flues, extracts), complete all penetrations through the envelope, and ensure the building is in a testable condition |
1. Air Tightness Testing — Energy Performance Evidence at Completion
The air tightness test is the definitive proof of building envelope airtightness. It measures the rate at which air leaks through the fabric of the building under a controlled pressure difference, providing quantified evidence that the constructed envelope meets the air permeability target assumed in the SAP or SBEM energy calculation. A failed result at completion is expensive to remedy because finishes, services, and decorations are already in place.
Under Building Regulations Part L (Conservation of fuel and power), all new dwellings in England must be air tightness tested. The result feeds directly into the SAP calculation and ultimately determines the Energy Performance Certificate (EPC) rating. If the tested air permeability is worse than the design assumption, the SAP calculation must be updated — and if the updated result fails to demonstrate Part L compliance, remedial work is required before the building can be signed off.
The test is carried out using a blower door — a calibrated fan temporarily sealed into an external doorway — which pressurises or depressurises the building to 50 Pascals. The measured airflow rate is divided by the envelope area to give the air permeability in m³/hr/m². Testing must be conducted by an ATTMA-accredited tester (or equivalent) to ensure the result is accepted by Building Control.
Test during construction, not just at completion
Conduct interim air tightness tests during construction — not just a final test — to identify and seal leakage paths before finishes cover them. Remedial sealing is far simpler and cheaper before plasterboard, skirting, and decorations are applied.
2. Air Tightness Test Record Fields
The following table sets out the fields captured in an air tightness test report. Each field contributes to demonstrating that the test was conducted correctly and that the result is valid for Building Control and SAP purposes.
| Field | Description |
|---|---|
| Project details | Site address, plot number, building type, and client details |
| Test date | Date and time the test was conducted |
| Tester | Name, ATTMA membership number, and accreditation details of the testing operative |
| Building envelope area | Total area of the thermal envelope (m²) used to calculate air permeability |
| Test type | Pressurisation, depressurisation, or both (ATTMA TS1 specifies the required method) |
| Equipment | Blower door model, serial number, and calibration date of the fan and manometer |
| Test conditions | Wind speed, external and internal temperature, barometric pressure at time of test |
| Preparation | Intentional openings sealed (trickle vents, flues, extracts), temporary seals recorded |
| Results at 50 Pa | Air permeability result in m³/hr/m² at the reference pressure of 50 Pascals |
| Design target | The air permeability value assumed in the SAP or SBEM calculation |
| Part L compliance | Confirmation of whether the tested result meets or exceeds the design target |
| SAP update required | Whether the SAP assessor must update the calculation based on the tested result |
| Signed | Signature of the accredited tester confirming the validity of the result |
3. Common Mistakes
Testing with intentional openings left unsealed
Trickle vents, flue terminals, extract fans, and other intentional ventilation openings must be temporarily sealed before testing. If left open, they inflate the measured air leakage and produce a result that does not reflect the true fabric airtightness. ATTMA TS1 specifies which openings must be sealed and which must remain open.
Not updating SAP if the result differs from the design assumption
If the tested air permeability is worse than the value assumed in the SAP calculation, the SAP assessor must update the calculation. If the updated SAP result fails to demonstrate Part L compliance, the building cannot receive a final EPC or Building Control sign-off without remedial measures.
Attempting remedy without first finding leakage paths
Applying sealant or tape indiscriminately is ineffective and wasteful. Smoke testing, thermal imaging, or a systematic walk-around during depressurisation should be used to identify the specific leakage paths before any remedial sealing is attempted.
Using a non-ATTMA accredited tester
Building Control bodies and SAP assessors require that air tightness tests are conducted by an accredited tester. A test conducted by a non-accredited person may not be accepted, requiring a re-test at additional cost and programme delay.
Leaving service penetrations unsealed before the test
Pipework, cable, and duct penetrations through the building envelope must be permanently sealed with appropriate airtight grommets, sleeves, or sealant before the air tightness test. Unsealed penetrations are one of the most common sources of air leakage.
4. Frequently Asked Questions
When is air tightness testing required?▾
All new dwellings in England must be air tightness tested under Building Regulations Part L. For non-domestic buildings, testing is required where the SAP or SBEM calculation includes an air permeability value (i.e. where the design relies on a specific level of airtightness to demonstrate Part L compliance).
What is a typical result for a well-constructed dwelling?▾
A well-constructed dwelling with careful attention to airtightness detailing typically achieves 3–5 m³/hr/m² at 50 Pa. The maximum permissible under Part L is 8 m³/hr/m², but most designs assume a target of 5 m³/hr/m² or better.
Who receives the air tightness test report?▾
The report should be provided to the client, the main contractor, Building Control (as evidence of Part L compliance), and the SAP assessor (who needs the tested result to finalise the as-built SAP calculation and issue the EPC).
Can the result be improved after a failure?▾
Yes. The leakage paths must first be identified — typically using smoke testing, thermal imaging, or a depressurisation walk-around — and then sealed with appropriate airtight materials. The building is then re-tested. Interim testing during construction greatly reduces the risk of failure at completion.
Generate your Air Tightness Test Record on Construction Suite
Construction Suite walks you through every required section with a guided Q&A — built to Building Regs Part L / SAP — and generates a professionally formatted document in minutes.
Get started freeThis guide is for general informational purposes only and does not constitute legal advice. While every effort is made to ensure accuracy, regulations change and individual project circumstances vary. Construction Suite is a trading name of Xzist Digital Ltd, registered in England and Wales.