Blower Door Air Tightness Test
Air pressure testing is mandatory under the Building Regulations for new homes since the 1st of July 2008. The procedure improves the energy efficiency of the building by pinpointing areas of heat loss (doors, windows, etc.). Air leakage through the building fabric demands more energy to maintain comfort.
Air leakage testing plays a vital role in achieving an A-rated home.
Equipment: Retrotec Q4E — NSAI Certified.
The Procedure
- Install a fan into the doorway of the main entrance of the house (no fixings applied).
- Seal all vents, flues, and extract fans.
- Pressurise to maintain an excess pressure of 50 Pa above outdoor.
- Measure airflow to determine air permeability, q50 (m³/hr·m²). Divide by 20 for an estimate of air changes per hour (ACH) under typical conditions.
Air Tightness Terminology
- Building envelope
- External elements of the building: walls, windows, front/rear doors, floors, ceilings.
- Air tightness
- Resistance of the envelope to inward/outward air leakage. Excessive leakage increases energy use and reduces comfort.
- Air leakage
- Unwanted airflow via gaps or cracks driven by pressure differences; typical at doors, windows, and between floors.
- Air permeability
- Leakage in m³/hr·m² of envelope at a 50 Pa differential; maximum permitted level is 5 m³/hr·m² @ 50 Pa for dwellings.
- Air changes per hour (ACH)
- Ventilation rate; controlled by MVHR or purge ventilation (opening windows/doors).
Building Regulations 2022 — Technical Guidance Document L
Conservation of Fuel and Energy — Dwellings
1.5.4 Air permeability pressure tests
Air permeability can be measured by means of pressure testing of a building prior to completion. The procedure for testing is specified in I.S. EN 13829:2000 “Thermal performance of buildings — determination of air permeability of buildings — fan pressurisation method”.
Additional guidance: BSRIA “Airtightness testing for new dwellings”, CIBSE TM 23 “Testing Buildings for Air Leakage”, and ATTMA “Measuring Air Permeability of Building Envelopes”. Preferred approach: controllable ventilator grilles temporarily sealed (not just closed).
Permeability is calculated by dividing the air leakage rate (m³/hr) by the envelope area (m²). Performance is assessed at 50 Pa. For dwellings, permeability at 50 Pa is approximately 20× the air change rate at normal conditions.
Schedule your blower door test
We’ll confirm availability, logistics, and pricing. Pre-test checks provided on booking.