Air Tightness Testing (Part L)
Accredited air permeability testing to satisfy Building Regulations Approved Document L. Same-day retests and certification for builders and self-builders.
What is Air Tightness Testing?
Air tightness testing (also known as air permeability or blower door testing) measures the volume of air that escapes through gaps and cracks in the building envelope.
It is measured as the rate of air leakage in cubic meters per hour per square meter of building envelope area at a reference pressure of 50 Pascals (m³/h/m² @ 50Pa). Under current Part L regulations, new houses must achieve a test result below their design target (typically 5.0 or lower).
Step-by-Step Testing Process
- Site Setup: Temporary sealing is applied only to mechanical ventilation and extraction fans. Internal doors are propped open to create a single air pressure zone.
- Blower Door Installation: A high-power fan is sealed inside an external doorway frame using an adjustable canvas frame.
- Pressurisation & Depressurisation: The fan is turned on to blow air into (and then suck air out of) the property, checking air flow rates at 50Pa.
- On-Site Results: Measurements are recorded, and target compliance is calculated instantly. Certification is generated same-day.
Common Air Leakage Pathways
Avoid failures by sealing these typical weak points in the building envelope before the test engineer arrives.
Service penetrations
Unsealed pipework under kitchen sinks, baths, vanity units, and utility spaces.
Skirting boards & floors
Gaps between bottom of plasterboard and floorboards, especially on suspended timber floors.
Loft hatches
Uninsulated hatches or lack of draft-excluding seals around the hatch opening.
Dry lining & ceiling joints
Air tracking behind plasterboard dab walls or around ceiling-to-wall interfaces.
Window & door frames
Poor perimeter sealing or defective gaskets between frames and brickwork masonry.
Recessed lighting
Unsealed downlights or light fittings piercing the ceiling vapor barrier into loft spaces.
Air Tightness Test & Quote Estimator
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Air Tightness Testing FAQs
Frequently asked questions about air pressure testing and building control sign-off.