Air Tightness Testing
Professional air permeability testing for new homes, commercial buildings and development schemes, helping demonstrate compliance, identify uncontrolled air leakage and support project completion.
Air Permeability Testing for New Buildings
Air tightness testing measures how much uncontrolled air escapes through gaps and joints in the building envelope. It is often required near completion so the measured result can be compared with the design target used within the energy assessment.
One Stop Consult coordinates air permeability testing for houses, apartments and commercial buildings. A site readiness checklist is provided before attendance so the contractor can confirm that the building is sufficiently complete and prepared for testing.
During the test, a calibrated fan is normally installed within an external doorway. The building is pressurised and depressurised while the technician records airflow and pressure data. The final result is expressed as an air leakage rate in m³/h·m² at 50 Pa.
Why Is Air Tightness Testing Required?
Uncontrolled air leakage can increase heat loss, reduce energy efficiency and make it harder for the completed building to achieve its intended performance.
Energy Compliance
The measured air permeability result can be used within the final SAP or SBEM assessment to confirm the completed building's performance.
Building Control Evidence
A test certificate may be required as part of the completion information provided to Building Control.
Quality Assurance
Testing helps identify defects around junctions, penetrations, openings and services before final handover.
Energy Performance
Reducing unwanted air leakage can lower heat demand and improve the relationship between design intent and actual performance.
How Does an Air Tightness Test Work?
The test uses a temporary fan system to create a controlled pressure difference between the inside and outside of the building.
Fan Installation
A calibrated fan and temporary frame are normally fitted within an external doorway.
Temporary Sealing
Openings that are permitted to be temporarily sealed for the test are prepared in accordance with the testing procedure.
Pressure Readings
The fan is operated through a range of pressures while airflow and pressure differential readings are recorded.
Leakage Calculation
The airflow required to achieve a 50 Pa pressure difference is divided by the building envelope area.
Understanding the Air Test Result
The result is normally reported as cubic metres of air leakage per hour for each square metre of building envelope at a pressure difference of 50 pascals.
A lower result indicates a tighter building envelope. The acceptable result depends on the design target and the energy calculation for the particular building.
Is Air Tightness Testing Mandatory?
Yes, for new homes. Part L expects an air pressure test on every new home before completion.
The Legal Limit
A new home must be no worse than 8 m³/h·m² at 50 Pa. Most SAP calculations set a tighter design target, and that is the figure your test has to meet.
New Commercial Buildings
These are tested too, against the target in the SBEM calculation. A building under 500 m² can avoid the test if the SBEM uses an assumed figure of 15 m³/h·m² at 50 Pa instead.
Conversions and Extensions
These don’t usually need a test, but one can help where the SAP assumed a better figure than the default.
Future Homes Standard
The new Part L for homes starts in England on 24 March 2027, and every new home will still need a test. It is worth checking your SAP target early. See our Future Homes Standard guide.
What Is a Good Air Test Result?
Any result at or below the design target in your SAP or SBEM passes. A lower number means a tighter building.
If the result is above the target but below the limit of 8, the SAP can sometimes be rerun with the measured figure. Ask us before you pay for remedial work.
Commercial Air Tightness Testing
New commercial buildings are pressure tested under Approved Document L Volume 2. The result is compared with the air permeability target in the SBEM calculation.
Which Buildings Are Tested
All new buildings that are not homes, plus extensions treated as new buildings under Part L. The main exceptions are buildings under 500 m² that use the assumed 15 m³/h·m² figure, and some factory-made modular buildings.
Level 1, 2 and 3 Testers
The ATTMA scheme has three tester levels. Level 1 covers buildings up to 4,000 m³ tested as one space with one fan. Level 2 covers any building tested as a whole, with several fans if needed. Level 3 covers complex buildings tested in zones.
What Building Control Asks For
Evidence that the tester is trained and registered for that class of building, and that the equipment was calibrated in the last 12 months, or as the manufacturer advises.
Planning a Large Test
Tell us the floor area, the height and whether the building hands over in phases. That sets the tester level and the number of fans, so the right team turns up.
When Is a Building Ready for Testing?
The envelope should be substantially complete and the building prepared so that the test reflects its intended finished condition.
External Envelope Complete
External walls, roof, floors, windows and external doors should be installed and capable of being closed.
Service Penetrations Sealed
Gaps around pipes, cables, ducts and other penetrations should be permanently sealed.
Internal Finishes Advanced
Plastering, drylining, skirtings and other elements forming part of the air barrier should be complete.
Windows and Doors Operational
Windows and external doors should be installed, adjusted and capable of closing correctly for the duration of the test.
Loft and Access Hatches Fitted
Hatches, riser doors and access panels forming part of the envelope should be installed and properly sealed.
Site Access Available
The technician requires clear access to the building, test doorway and relevant areas during attendance.
Where Do Buildings Commonly Leak Air?
Air leakage often occurs at junctions and penetrations where different trades or building elements meet.
Windows and External Doors
Poorly sealed frames, thresholds, hinges and perimeter joints can create significant leakage paths.
Service Penetrations
Pipework, cables, meter boxes, ducts and waste connections should be sealed where they pass through the air barrier.
Wall-to-Floor Junctions
Gaps behind skirting boards or at floor edges can allow air to track through cavities and concealed spaces.
Ceilings and Roof Junctions
Loft hatches, eaves, rooflight details and ceiling penetrations can contribute to leakage at high level.
Drylining and Sockets
Air can move behind plasterboard and escape through sockets, switches and unsealed board junctions.
Risers and Boxing
Service risers, boxing and concealed voids can link internal spaces with unsealed parts of the envelope.
What Happens During the Site Test?
The technician will review the building condition, install the fan equipment and prepare the property for the test. Internal doors are generally opened while windows and external doors remain closed.
Other contractors may be able to continue working elsewhere on site, but the test area must remain controlled. Windows and doors must not be opened while readings are being taken, and activities that affect building pressure may need to pause temporarily.
What Happens If the Building Fails?
A failed result means the measured air leakage is higher than the allowable design target. The next step is to identify and seal the most significant leakage paths before arranging a retest.
Leakage Review
Review the failed result and likely areas of uncontrolled air movement.
Remedial Sealing
Seal identified gaps around junctions, services, doors, windows and concealed voids.
Retest
Repeat the air permeability test once the building has been prepared and remedial work is complete.
Air Sealing and Pass Support
Where a building fails and the completion programme is under pressure, additional leakage investigation and sealing support may be available. This can help identify the main defects and complete targeted remedial work before retesting.
The scope and cost depend on the size of the scheme, the failed result, the design target and the accessibility of the leakage paths. Details should be confirmed after the initial test or leakage review.
How the Air Tightness Testing Process Works
Early coordination helps ensure the correct plots are selected and the site is genuinely ready when the technician attends.
Quotation
Review the number of plots, building type, location and required test programme.
Readiness Check
Confirm that the building envelope and relevant finishes are complete before attendance.
Site Testing
Install the calibrated fan equipment and record airflow readings across the pressure range.
Result Review
Compare the measured air permeability with the required design target.
Certification
Issue the successful test documentation for the project team and Building Control.
Information Required for a Quotation
Provide the full site address, building type, number of plots or units, expected testing date and the air permeability target.
For larger developments, confirm the plot schedule, construction types and whether testing is required in phases. The latest SAP or SBEM information is also useful where available.
Air Tightness Testing for a Range of Buildings
Nationwide Air Tightness Testing Service
One Stop Consult coordinates air permeability testing for residential and commercial projects throughout mainland UK. Support is available for individual properties, phased developments and larger multi-building schemes.
We also have local pages for air tightness testing in Birmingham, Bristol, Coventry, Leeds, Leicester, Liverpool, London, Manchester, Nottingham and Sheffield.
Other Services Your Project May Require
Important Air Tightness Testing Information
The building must be sufficiently complete and prepared before testing. The required result depends on the design energy assessment and project specification. Delays, aborted visits or failed tests may result where the envelope is incomplete, doors and windows are not operational, or service penetrations remain unsealed. The final result should be passed to the relevant energy assessor and Building Control body. One Stop Consult provides consultancy and coordination support through its specialist testing network.
Air Tightness Testing FAQs
What is an air tightness test?
It measures uncontrolled air leakage through the building envelope using a calibrated fan and a controlled pressure difference.
What does 50 Pa mean?
It is the standard pressure difference used to report the air leakage rate during the test.
How is the result expressed?
The result is normally expressed as m³/h·m² at 50 Pa, representing airflow per square metre of building envelope.
Does a lower result mean the building is tighter?
Yes. A lower measured air permeability indicates less uncontrolled air leakage through the envelope.
Can contractors continue working during the test?
Work may continue in some areas, but external doors and windows must remain closed and the test zone must stay controlled.
What happens if the property fails?
Leakage paths should be identified and sealed before the building is retested.
When should the test be booked?
Book early enough to secure the required date, but only test once the building envelope and relevant finishes are complete.
What information is required for a quote?
Send the site address, number of plots, building type, target result and expected testing date.
Do you provide Air Tightness Testing nationwide?
Yes. We coordinate suitable testing support for eligible projects throughout mainland UK.
Is Air Tightness Testing mandatory?
Yes for every new home under Part L, and for most new commercial buildings. Conversions and extensions don’t usually need one.
What is a good air test result?
Any result at or below the design target in your SAP or SBEM. The limit for a new home is 8 m³/h·m² at 50 Pa, and most design targets are tighter.
How much does an air tightness test cost?
From £95 + VAT (per plot). Guide price. Get a free quote for your project.
Do commercial buildings need an air tightness test?
Yes, most new ones do. A building under 500 m² can avoid the test if the SBEM uses the assumed figure of 15 m³/h·m² at 50 Pa, and some factory-made modular buildings are also exempt.
What is a Level 2 air tightness tester?
A tester registered to test any building as a whole, using several fans if needed. Level 1 stops at 4,000 m³ with one fan, and Level 3 covers complex buildings tested in zones.
What is the air tightness standard in the UK?
In England, Part L sets a limit of 8 m³/h·m² at 50 Pa for a new home, and most SAP calculations set a tighter design target. Approved Document L says tests should follow CIBSE TM23, the approved testing method.
Will Building Control accept the air test certificate?
Building Control can accept a certificate from a tester registered with one of the organisations listed in the Building Regulations. It should also see evidence that the test equipment has been calibrated, which must happen at least once every 24 months.
Does an extension need an air tightness test?
Not usually. Approved Document L asks for a test on new homes and new commercial buildings, not on extensions. A test can still help where the SAP for an extension or conversion assumed a better figure than the default, because the measured result can then be used. Ask us if your SAP assessor or Building Control has asked for one.
How can I test the air tightness of my house?
Only a proper air test counts for Building Control. A qualified tester fits a fan into an external door, raises the pressure inside to 50 Pa and measures how much air leaks out, then issues a certificate. You can look for leaks yourself on a cold or windy day by feeling for draughts around windows, doors, the loft hatch, pipes and sockets, but that is a check, not a result. If you are building a new home, book the test near the end of the build, once the checks in the readiness section above are done.
Request Your Free Air Tightness Testing Quote
Complete the form below with the site address, building type, number of plots and expected test date. Include the required air permeability target and any available SAP or SBEM information so our team can review the requirement and coordinate an appropriate quotation.
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