What is a Good Air Tightness Score?

by | Jun 3, 2024 | Air Permeability Testing, Last Articles | 0 comments

Hello and welcome to the Building Compliance Testing Limited blog! Today, we’re going to discuss a topic that’s crucial for both new builds and existing dwellings: air tightness. More specifically, we’ll explore what constitutes a good air tightness score.

Understanding Air Tightness

Air tightness, often known as air permeability, measures the amount of conditioned (heated or cooled) air leaking from a building through uncontrolled ventilation. A good air tightness score indicates a low level of air leakage. The lower the air change rate (ACH) or cubic feet per minute (CFM) result, the more airtight the building is.

Scoring Air Tightness

Scoring for the air permeability test ranges 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. In general, a result of less than 0.6 ACH is considered very good, while anything above 1.5 ACH indicates that there is significant room for improvement.

New Builds vs Existing Dwellings

For new dwellings, the Building Regulations Part L specifies that air leakage can be no more than 10m3/h/m2 @50Pa. However, the new maximum target for air tightness is <8m3/ (h·m2)@50Pa, which is a 2 point reduction from the current maximum of 10. This more airtight target allows for low temperature heating systems such as air source heat pumps to be viable and meet the reduced carbon emissions targets.

For existing dwellings, improving air tightness can be more challenging due to the structure and materials used in older buildings. However, it’s still possible to achieve a good air tightness score with proper sealing and insulation.

Regulation Requirements and Part L

The Building Regulations Part L in the UK sets standards for the energy performance of new and existing buildings. It specifies that air leakage can be no more than 10m3/h/m2 @50Pa. However, the new maximum target for air tightness is <8m3/ (h·m2)@50Pa.

ATTMA Details

The Air Tightness Testing & Measurement Association (ATTMA) is a professional association dedicated to promoting technical excellence and commercial effectiveness in all air tightness testing applications. ATTMA has grown with the air tightness testing industry, creating standards such as TSL1 and TSL2 that are internationally recognised.


Achieving a good air tightness score is crucial for both new builds and existing dwellings. Not only does it contribute to energy efficiency and lower running costs, but it also helps meet regulation requirements and standards set by Part L and ATTMA. Remember, the key to a good air tightness score starts with proper planning, preparation, and understanding of requirements.

Stay tuned to our blog for more insights into building compliance testing. If you have any questions or need assistance with air tightness testing, don’t hesitate to contact us at Building Compliance Testing Limited.