Air Tightness Testing

Air tightness testing is a requirement on new build properties and is highly advised on retrofit and change of use projects.
The test determines the air leakage rate of a building.

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Also known as an air leakage or air permeability testing, air tightness testing takes place to ensure that the building is constructed to an energy efficient standard. The test is carried out at completion of the build however intermediate testing is advised to ensure problem areas can be determined early in construction.

An Air Tightness Test is required on new build properties under Part L1A and ensures the building meets the minimum standard set by the government. 

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Although testing is not a Building Regulations requirement on conversions, change of use or retrofit projects, we highly advise that this is undertaken to ensure you have a sufficient level of air tightness to reduce heat loss and protect the building structure and insulation from moisture damage. 

The lowest allowable case in the UK for new build projects is is 10m3h1m2. However, most SAP calculations will have a target of around 5m3h1m2 or lower to ensure that the emissions target in SAP is achieved. If you are aiming for the Passivhaus standard of building then the target is 0.6 air changes per hour (Passivhaus is based on volume and is not directly comparable to Building Regulations however this would generally equate to a Building Regulations result of under 1m3h1m2

Air leakage occurs through gaps and cracks in the building fabric, this allows heat to escape and can have a significant impact on annual heating bills and CO2 emissions. Air leakage can also damage the buildings structure and insulation as warm moist air will condensate when reaching colder areas within a wall, floor or roof construction.

Fully accredited and highly experienced engineers

  • iATS accredited engineers
  • All tests are formerly lodged meaning they are always Building Control compliant.
  • Our engineers are audited annually
  • All tests are carried out in line with ATTMA TSL1/2.

We strive to go above and beyond the service that many air testing firms provide. We are renowned for our level of service on-site, and if there are problems with achieving your target figure we always aim to not only identify the air leakage paths but, where possible, get them fixed while on site to avoid costly retests. 

As standard, we provide free advice throughout the build to all clients who book a SAP and air tightness package with us.

Air Tightness Testing

Free Air Leakage Paths Guide

When you book or when we complete your Design Stage SAP Calculation, we’ll send you a copy of our free ‘Thinking About Air Tightness’ guide.

The guide shows real-life example of the best and worst of what we have found on-site, allowing you to ensure you’re building an airtight dwelling and giving you a great point of reference to check over before your test visit.


For Passivhaus and other low energy buildings we recommend following guidance in the Passivhaus Trust guide called ‘Demystifying Airtightness’ found here. Contact us to discuss our full air tightness consultancy and design review service. 

For more information on Air Tightness Testing, how to pass and when you need to have them carried out, scroll down to our Air Tightness FAQ’s

Frequently Asked Questions

An air tightness test measures the level of air leakage in a dwelling. The test is used in the SAP calculation (or SBEM calculation if the building is commercial) to help the building achieve the emissions and fabric efficiency targets. The worst allowable case in the UK is 10m3h1m2 however most SAP/SBEM calculations will have a target of around 5m3h1m2 or lower to ensure that the emissions target in SAP is achieved. Passishaus targets are much more stringent with a target of 0.6ACH (air changes per hour and based on building volume).

Air leakage occurs through gaps and cracks in the building fabric, this allows heat to escape and therefore increases annual heating bills, CO2 emissions and reduces comfort levels. 

The performance level of the insulation you install is greatly reduced if cold air can leak in around it and
even more reduced if warm moist air enters the construction. This warm air then condenses on the cooler insulation and timbers causing damp issues, increased heat loss and, over time, potential structural problems.

Air tightness is achieved throughout the build… not at the end. It is important to ensure all of your trades understand the level of air tightness you are aiming to achieve and understand what is required of them.

There are many products on the market which are great at helping achieve airtightness and we advise you use them where you can. Our ‘Thinking About Airtightness’ guide will help guide you through each stage of the build and ensure you are considering air tightness throughout. We also have a checklist which will help guide you through each stage. It is available here. For Passivhaus or low energy buildings much more strict measures will need to be put in place compared to achieving targets for UK Building Regulations compliance.

When aiming for a high level of air tightness we advise you receive project specific advice from the design stage onwards. For further advice please contact us.

The short answer is: ‘the more airtight the better’. This is because the more airtight the building is; the less heat it will lose in the winter. 

There are, however, other things to consider. Ventilation is extremely important in any building: Where natural ventilation is being used (this is where there is an extractor fan in each ‘wet’ room and trickle vents throughout) then the lowest you should be going for air tightness is 3.00 m3h1m2 . Anything below this figure and there will not be enough air movement in the building; increasing the risk of condensation, damp and potentially causing poor air quality. 

If you are installing a mechanical ventilation system with heat recovery (which we highly recommend), then you should be going as low as possible; the lower the better. Your ventilation system (if set up & commissioned correctly) will ensure the dwelling is ventilated properly and will work even more efficiently at low air tightness figures.

For a new build dwelling your target will be set within your SAP calculation, under Part L1A. For Passivhaus certification you will need to achieve 0.6ACH (air changes per hour) or 1.0ACH for EnerPHit.

This should be at completion, once the fabric of the building is complete and all kitchen and bathrooms have been installed.

We advise that an intermediate test is carried out where air tightness is a key part of the building strategy or where you are not experienced at achieving low scores. This allows any problem areas to be identified before they are hidden by final finishes or plasterboard layers. For Passivhaus certification the intermediate tests are essential.

Click here for a copy of our stage by stage checklist when looking to achieve UK Building Regulations. For Passivhaus we recommend reading the Passivhaus Trust guide called ‘Demystifying Airtightness’ found here and that you contact us to discuss our airtightness design review and full consultancy service.