Air Tightness Testing for Building Regulations Compliance
Certified air testing for new builds and commercial properties across the UK
Meet air permeability requirements hassle-free with JosTec’s ATTMA-accredited engineers
What is an Air Tightness Test?
An air tightness test, also known as an air pressure test, air permeability test, air leakage test or air test, measures how much air escapes from a building as a result of uncontrolled leakage through gaps and cracks in its structure.
This test plays a vital role in assessing a building’s energy efficiency and identifying areas of poor build quality to ensure that the dwelling(s) don’t allow heating to escape, thus increasing carbon emissions.
It is also required for compliance with part L of UK Building Regulations.
Is Air Tightness Testing Mandatory?
Yes. Under Building Regulations Part L, air tightness testing is mandatory for all new build homes and most new commercial buildings. It is not usually required for extensions or conversions.
However, we advise anyone doing any building works to have an air tightness test. A lack of attention to air leakage can result in:
- Dampness and/or rising damp
- Excessive heat loss
- Increased heating and energy bills
- Drafts
- Reduced comfort for those living inside the property
As a property developer, builder or landlord, these consequences could make all the difference when it comes to selling or renting a property.
Do You Need an Air Test for an EPC?
The answer is, it depends.
An air test is mandatory for all new build properties in the UK. Building Regulations set a maximum air permeability rate of 8.0 m³/hr·m², but in most cases the Full SAP Calculation will specify that a lower score is required in order
to comply with fabric and emissions targets.
For conversion properties, an air test isn’t required under Building Regulations. However, air testing is increasingly shown to help to boost EPC scores up a banding, making it a valuable option to consider.
For existing properties, air testing was not previously an option. However, with the release of RdSAP 10 it is now possible to carry out an air test and use the result to improve the EPC rating—often raising a property from, for example, a D to a C. This can be particularly significant for landlords aiming to meet new MEES requirements.
When to Do an Air Tightness Test
An air test is usually carried out before the second fix stage. You’ll need to ensure:
- All external windows and doors are installed
- All major service penetrations have been made
- All sealing works are complete
- Power is available on site (110v or 240v)
How is an Air Tightness Test Done?
To carry out an air tightness test:
- The building must be empty and sealed
- A blower door fan is installed in an external doorway (typically the front door)
- All external doors and windows are shut; internal doors remain open
- The fan depressurises the building to at least -50 Pascals (Pa)
- An anemometer measures:
-Internal and external pressure
-Airflow needed to maintain the pressure difference - The engineer takes 10 readings at various pressures, factoring in temperature and barometric pressure
- Data is processed by specialist software to calculate the building’s air permeability rate
Results are shown as m³/h/m² – cubic metres of air lost per hour, per square metre of the building envelope (walls, floor, and roof).
Lower results indicate better airtightness and therefore greater energy efficiency.
What Happens if You Fail an Air Test?
Failing an air tightness test means the building has excessive air leakage and does not comply with with either Part L of the Building Regulations or the target score set out in you SAP calculation.
A retest will be required after remedial sealing or insulation work is completed
Support If Your Building Fails
If your building doesn’t pass the first time, we’ll do everything we can to help within a reasonable timeframe to support a successful same-day retest.
To speed up the process, we recommend having materials like mastic sealant and expanding foam ready on site. During the test, our engineers can point out air leakage areas. If the issues are minor and can be sealed immediately, we’re happy to wait while quick fixes are made, then retest the building the same day to give you the best chance of passing
Why Choose JosTec?
With hundreds of SAP assessments delivered across the UK, we know what Building Control needs and we make sure you get it, fast.
- 500+ SAP reports delivered
- OCDEA accredited team
- Fast 24-48hr turnaround
What's Included
How it Works
Getting your SAP calculation is simple. Whether you're a developer, architech or self-builder, we handle the technical side and deliver exactly what Building control needs - fast
Frequently Asked Questions
Air tests are usually carried out just before the second-fix stage, once the building is sealed but still accessible. You’ll need to ensure:
- All external windows and doors are installed
- Major service penetrations are complete
- Sealing works are finished
- Power (110v or 240v) is available on site
Booking your test at this stage helps avoid delays and ensures compliance before completion.
You can download our site readiness checklist to review before you book your air tightness test.
Failing a test means your building has excessive air leakage and doesn’t meet the target set by Part L or your SAP calculation.
Our engineers will identify where the air is escaping and advise on quick remedial fixes - such as sealing gaps or applying mastic. If the issues are minor, we can often wait while they’re repaired and retest the same day, helping you pass and stay on schedule.
See common sources of air leakage in properties →In most cases, yes – but the link is via your SAP Calculation rather than the EPC itself. For new residential and many commercial buildings, you’ll need an air tightness test so that your SAP Calculation can be completed and passed. Once your SAP is signed off (using the measured air test result), your EPC can then be lodged.
For existing or conversion properties, testing isn’t mandatory but can improve EPC performance, especially with the latest RdSAP 10 update, which allows measured air test data to raise a property’s rating - sometimes by a full band.
Learn more about EPCs →A calibrated blower-door fan is fitted to an external doorway to pressurise and depressurise the building. With all external openings closed and internal doors open, the engineer records airflow and pressure differences at multiple points.
Specialist software then calculates the air permeability rate (m³/h/m²) - the amount of air leaking per hour through each square metre of the building envelope. Lower figures indicate better airtightness and improved energy efficiency.
Building Regulations set a maximum rate of 8.0 m³/hr·m², but most new builds are designed to achieve 5.0 m³/hr·m² or lower to meet SAP and emissions targets.
For conversions and existing properties, there’s no legal requirement, but lower readings generally mean reduced heat loss, lower bills, and better EPC outcomes.
Air leakage is the uncontrolled flow of air through cracks, joints, and service penetrations in the building fabric. It causes heat loss, drafts, condensation, and higher heating costs. Reducing leakage improves comfort, efficiency, and building longevity.
Why air tightness is so important →Ensure that all service penetrations are sealed, trickle vents are installed, doors and windows are fitted with seals, and plumbing is complete.
Before testing, make sure your site is ready:
- All service penetrations sealed
- Trickle vents installed
- Windows and doors fully fitted and sealed
- Plumbing and electrics complete
- Power available on site
You can download our site readiness checklist to ensure everything’s prepared for a smooth test.
Get Your Quote for Overheating Calculations
Get started with a free, no-obligation quote for your overheating assessment.
We offer fast scheduling, expert engineers, and support to help your building achieve compliance
Additional Services to Support Your Project
Need help with more than Overheating Calculations?
Explore our other services to help you navigate building regulations and achieve compliance.