What Air Test Score Do I Need for My New Build? | Part L 2026 Guide
If you are currently mid-build or planning a new project, understanding air permeability targets is critical for passing your final Building Control inspections.
With the transition from Part L 2021 to the 2026 Future Homes Standard, the "pass" requirements are becoming more nuanced. Here is a breakdown of the scores you need to hit to ensure compliance.The Legal Limit vs. The SAP Target
Under Approved Document Part L, there is a difference between the maximum allowable limit and the score you actually need to pass your SAP assessment.
1. The Maximum Limit (The "Backstop")
The absolute maximum air permeability allowed for a new build remains 8.0 m³/(h·m²) at 50Pa. This figure is unchanged in the updated Part L 2026 regulations. If your building scores higher than an 8, it is an automatic fail.
2. The Notional Dwelling Target (The "Real" Goal)
While an 8 is the legal limit, the SAP (Standard Assessment Procedure) calculations use a "notional" target to set your energy benchmarks.
- Part L 2021: The notional target was 5.0 m³/(h·m²).
- Part L 2026: This is tightening to 4.0 m³/(h·m²).
Why does this matter?
If your air test score is higher than the notional target (e.g., you score a 7), your building’s fabric - such as insulation or glazing - must perform better than standard to compensate for the heat loss. In short, a better air test score (closer to 4 or 5) makes it much easier to pass your overall SAP rating.
The "Sweet Spot" for Air Tightness
- Aim for 4.0 – 5.0: This is the most common target for modern new builds to ensure a SAP pass without over-specifying other materials.
- Beware of going below 3.0: If your building is too airtight (scoring below 3), you will likely be required to install mechanical ventilation (MVHR) to ensure adequate indoor air quality and prevent damp.
Why Choose UK Building Compliance for Your Air Test?
Achieving the perfect balance of airtightness requires expertise. At UKBC, we don't just provide a certificate; we provide the support to ensure you pass the first time.
- Video Diagnostics: Real-time visual assistance to identify leakage paths during the test.
- Technical Assistance: Expert guidance on how to improve your score and achieve a pass.
- Nationwide Coverage: Fast, reliable testing across the UK from our Hinckley base.
- Integrated Service: We coordinate your Air Testing directly with your SAP Calculations for a seamless compliance journey.
Get Your Air Test Quote Today
Don't leave your compliance to chance. Consult with your SAP Assessor early to confirm your specific target, and let UKBC handle the rest (we can even handle your SAP too if required!).
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