When should an air pressure test be booked?

Book early enough to allow preparation, but plan the test for when the building envelope and relevant service penetrations are complete. The right stage depends on the project and evidence required.

Part L · air permeability

Air Tightness Testing Across England

Q: What happens if a building misses its target?

The result can guide investigation of leakage paths. Remedial work and a retest may then be appropriate, subject to the project design and Building Control requirements.

Air pressure testing for new-build homes, extensions and commercial projects, with practical preparation guidance and clear evidence for your project team.

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What the test does

Measure uncontrolled air leakage through the building fabric

Air tightness testing—also called air pressure, air leakage or air permeability testing—uses a calibrated fan to create a pressure difference across the building envelope. The measured airflow is used to calculate the result required by the project.

New-build dwellings

Testing can form part of the Part L evidence required before completion. The project’s SAP assessor and Building Control team should confirm the target and test scope.

Commercial buildings

Non-domestic projects may also need air permeability evidence. Building size, design documentation and the required test standard help determine the setup.

Conversions and extensions

Requirements vary. Share the approved design and Building Control request so the correct evidence can be discussed before a booking is made.

From enquiry to report

A practical testing process

Confirm scope

We review the address, building type, target, drawings and the stage of work.

Prepare the site

You receive guidance covering the envelope, openings, traps and service penetrations.

Complete the test

The fan and pressure equipment are set up and readings are taken under the agreed method.

Issue the result

The measured result and relevant report information are provided for the project record.

Site readiness

Prepare before the appointment

A test is most useful when the intended air barrier is complete and accessible problems have been resolved before the visit. Typical preparation includes:

Complete and close external doors and windows.
Finish or temporarily seal intended openings and service penetrations in line with the agreed test method.
Fit loft hatches, access panels, sockets and other envelope components.
Fill water traps and make fireplaces, flues and ventilation systems ready for the test method.
Keep internal doors open and provide safe access to the whole test area.
Have the target, drawings and relevant Building Control or SAP information available.

Every project is different. Confirm the required test method and preparation before sealing anything permanently.

Common questions

Air testing FAQs

Are air tightness testing and air pressure testing the same?

The terms are commonly used for the same fan-pressure test used to measure uncontrolled leakage through a building envelope. “Air permeability” describes the calculated result used for many compliance projects.

When should I book the test?

Book early enough to secure a suitable date and allow preparation. The final compliance test is normally planned when the envelope and relevant penetrations are complete, but the exact stage depends on the project.

How long does testing take?

It depends on building size, access, preparation and the evidence required. Send the plans and property details for a realistic appointment allowance.

What happens if the result misses the target?

The test result can guide investigation of leakage paths. Remedial work and a retest may then be appropriate, subject to the design team and Building Control requirements.

Do all new homes need the same target?

No. The required result comes from the project design and compliance route. Confirm the target with the SAP assessor or design team before the test.

Related services

Keep connected compliance work together

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Air tightness scheme credentials

Approved scheme membership supporting professional air tightness testing, clear site guidance and project reporting.