Building your own home? Here’s why airtightness matters
For any self-build project in the UK, air tightness testing, often called an air permeability test or blower door test, isn’t just a box to tick for Building Regulations Part L.
It’s how you prove your new dwelling is energy-efficient, comfortable, and compliant with CIBSE TM23 (2022) and BS EN ISO 9972:2015.
Poor airtightness means draughts, higher bills, and failed compliance certificates. Getting it right early avoids delays and costly remedial work once the house is finished.
What is air tightness testing?
Air tightness testing measures how much uncontrolled air leaks through gaps and cracks in your building envelope when pressurised to 50 Pa.
The result is expressed in m³/h·m² @ 50 Pa, the lower the number, the tighter the building.
Typical self-build dwellings aim for ≤ 5 m³/h·m², though many target 3 or lower to meet SAP/EPC goals and qualify for green-building standards such as Passivhaus.
When should self-builders arrange the test?
You’ll normally test toward completion, once:
- All windows, doors, and service penetrations are sealed
- Mechanical ventilation systems (e.g., MVHR) are installed
- Internal finishes are substantially complete
However, many self-builders book an interim test earlier, before plastering, to catch hidden leaks while fixes are still easy.
The process: what to expect
- Preparation – Ensure loft hatches, extractors, and trickle vents are temporarily sealed. Follow your tester’s prep checklist.
- Testing – A calibrated fan (blower door) depressurises and pressurises the building. Sensors record airflow rates at different pressures.
- Results & certification – You’ll receive an ATTMA-approved test report and certificate, required by your Building Control Officer for Part L sign-off.
- A typical single-dwelling test takes 60–90 minutes, with same-day results.
How to prepare your self-build for a pass
Small details make the biggest difference. Before your final test, check:
- Gaps around pipe and cable penetrations
- Joist ends and service voids
- Loft hatches, recessed lights, and wall sockets
- Window and door seals (especially thresholds)
- Around extractor fans and trickle vents
Use airtight membranes and tapes wherever services penetrate the envelope.
Tip: Many self-builders fail their first test simply due to missed sealant behind skirting boards or poorly foamed window frames.
Cost and booking
For a single new dwelling, UK test prices typically range £150–£250 depending on location, size, and number of units.
Nationwide providers like Air Tightness Solutions offer same-week availability and certificates within 48 hours.
Understanding your result
Your test certificate will show:
- Air permeability value (m³/h·m² @ 50 Pa)
- Pass/fail against your SAP target
- Any identified leakage points
If you fail, retesting is quick once remedial work is complete. Most issues can be fixed with basic sealant and taping.
Why early planning pays off
Integrating airtightness into your design from day one rather than leaving it to the test day saves time and money.
Brief your architect and trades early: airtightness is a design responsibility as much as a construction one.
Key takeaways for self-builder
✅ Plan airtightness details during design.
✅ Choose ATTMA-registered testers familiar with self-build projects.
✅ Conduct an optional pre-plaster test to de-risk compliance.
✅ Target ≤ 5 m³/h·m² for standard builds (or ≤ 3 for high-performance homes).
✅ Keep your test certificate safe, it’s required for your EPC and Building Control.
Ready to Book Your Test?
Don’t leave your compliance to chance. Our ATTMA-registered engineers carry out Part L-compliant air tightness tests nationwide, with fast turnaround and clear guidance for self-builders.
👉 Book your air tightness test today and get your certificate within 48 hours.