In modern construction, achieving a good air tightness result is essential—not just for meeting building regulations, but for improving energy efficiency, indoor comfort, and long-term sustainability. But what exactly defines a good air tightness score?
Let’s explore what you need to know.
What is Air Tightness?
Air tightness (also known as air permeability) measures how much air leaks through a building’s external envelope. It’s tested typically using a blower door test, which pressurises or depressurises the building to detect and quantify air leakage.
The result is expressed as:
m³/(h·m²) @ 50Pa
(Cubic metres of air leakage per hour, per square metre of envelope area, at 50 Pascals pressure)
Part L Building Regulations for Air Tightness
According to Approved Document Part L (2021), the maximum allowable air permeability for new dwellings is:
8 m³/(h·m²) @ 50Pa
However, most homes are expected to perform better. The actual target is often set by SAP (Standard Assessment Procedure) calculations, which consider insulation, thermal bridging, and renewable technologies.
What Is a Good Air Tightness Score?
Here’s a quick guide to interpreting your test result:
| Air Tightness Score | Performance | Implications |
|---|---|---|
| < 3 m³/(h·m²) | Excellent | May require mechanical ventilation (MVHR) to prevent moisture and air quality issues |
| 3–5 m³/(h·m²) | Good | Efficient, compliant, and well-balanced for energy and ventilation. A DMEV, CMEV ventilation strategy is recommended |
| 5–8 m³/(h·m²) | Acceptable | Meets minimum standards but may not optimise energy performance. A IEV ventilation strategy is sufficient |
| > 8 m³/(h·m²) | Poor | Fails compliance; remedial work required to pass testing |
A score just under 5 is widely considered the industry average and a reliable benchmark for most residential builds.
Air Permeability and Insulation
Air permeability and thermal insulation work hand in hand to define a building’s thermal performance. While thermal insulation slows down the transfer of heat through walls, roofs, and floors, air permeability controls the unintended movement of air through gaps and cracks in the building envelope. Even the best insulation can be compromised by poor air tightness—small leaks can lead to significant heat loss, increased energy bills, and reduced comfort. To achieve optimal energy efficiency and indoor climate control, both insulation and air tightness must be carefully designed and executed together.
Reducing Draughts and Ventilation
While aiming for high air tightness, it’s equally important to plan for effective ventilation to maintain healthy indoor air quality. This often involves integrating Mechanical Ventilation with Heat Recovery (MVHR) systems, which supply fresh, filtered air while extracting stale air and recovering heat in the process. MVHR ensures moisture control and comfort without compromising the building’s thermal efficiency—striking the perfect balance between airtight construction and breathable living spaces.
Why Reducing Air Infiltration Matters
- Energy Efficiency: Reduces heat loss in winter and heat gain in summer, lowering energy bills and carbon emissions.
- Comfort: Helps maintain a stable indoor temperature.
- Health: Supports good indoor air quality when paired with proper ventilation.
- Compliance: Required for building sign-off and energy performance certification.
Tips For Achieving a Good Air Test Result
- Design Smart: Minimise complex junctions and potential leakage points.
- Use Quality Materials: Select high-performance, compatible air-sealing products.
- Build with Precision: Ensure airtight detailing during construction.
- Plan Ventilation: Incorporate MVHR systems where needed.
- Test Early: Conduct interim blower door tests to identify and fix issues before final testing.
ATTMA Accredited Compliance Engineers
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.
All our engineers are at least Level Air Tightness Testers and hold current registration with the Air Tightness Testing & Measurement Association (ATTMA). We have over 10 years on-site experience – you are in good hands.
Our testing is routinely carried out using a blower door. Following the methodology to ATTMA standards in line with CIBSE TM23 or ISO 9972:2015.
Are you looking for an Air Test?
It’s essential to conduct an Air Test for all dwellings including existing homes, new-builds and conversion or extension projects. Air Permeability Testing assesses the level of conditioned (heated or cooled) air leakage from a building through uncontrolled ventilation.
By ensuring that the building meets or exceeds the air permeability rating specified in a design stage SAP or SBEM Calculation, Air Permeability Testing guarantees energy efficiency and performance. This helps achieve the best possible Energy Rating of your Energy Performance Certificate.
Learn more by visiting our Air Permeability service page, by clicking here.
Have a Project in mind? Let’s get to work!
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.