Air Tightness Explained

What is an air permeability test?

An air permeability test is a process of inducing a set of environmental conditions on the buildings envelope to be able to measure the uncontrolled movement of air similar to the effect wind would naturally have on the building at equivalent wind speed of 20 meters per second.

To achieve this we use large door blower fans to create a pressure differential between inside and outside of the building. Using calibrated UKAS testing equipment these pressures are used to measure the air flow through the door blower fan which enables us to calculate the overall air permeability score.

Why test?

Being able to identify the volume and location of uncontrolled air movement within a building enables targeted improvement work to be carried out to reduce cold draughts  and improve indoor air comfort. This will help improve your the CO² & SAP rating.


In simple terms uncontrolled air movement use excess energy to heat the dwelling that is being wasted, when air is allowed to escape the buildings insulated fabric. As a result the heating system has to work harder to replenish that loss of heat, costing money and unnecessary emitting carbon emissions. This is why within the SAP Calculation & SBEM Calculation the process of lowering the “design or assumed” air permeability rating helps improve the dwelling emission rate (DER) or building emission rate (BER) making the energy compliance easier and improving the EPC rating.


Alternatively you can "opt-out" of air permeability testing but you will be required to use a default figure of 15 m³/hr/m² within the SAP calculation which means additional measures are required to compensate for the additional heat loss.  This usually means increasing the level of insulation to floors, walls & roof's, improving glazing or heating systems which are all generally more expensive than the air test anyway.

How is air permeability scored?

Scoring for the air permeability test is between 0 - 10 m³/hr/m² @ 50 pascals, with zero being the most air tight score and ten being the maximum allowable by Building Regulations. The assumed or design air permeability rate is usually dictated by either the SAP or SBEM calculation completed during the design stage.

What should I target for my score? 

Whilst the maximum result can be upto 10m³/hr/m² here at BEAT Solutions we recommend a target of 5m³/hr/m² @ 50 pascals. This represents a modest score which is slightly better than the national average and is very achievable without the need for specilaist products. Additionally, the this score will help lower the buildings CO² emissions, help reduce running costs and improve the SAP or SBEM calculation score for building regulation compliance.


If yours interested in lowering your target score even more, we offer a detailed design review service which will help ensure your buildings design is airtight.

When is the air permeability test done?

The air permeability test is required once the building is complete and prior to occupation.

We therefore recommend the test is booked once the property is painted and decorated with all the floor coverings having been installed and the mastic sealant has been completed. This is often at a similar time to the finals and cleaning stage. Importantly the property must have the electricity supply on and properly working.  

Use our air permeability readiness checklist to ensure your next project gets the best possible result.