Written by Andrew Champness
A blower door test is a diagnostic test used to measure how airtight a building is. It identifies how much air leaks through the building envelope (the walls, ceilings, floors, windows, doors and service penetrations that separate the inside of a building from the outside).
The test uses a large specialist and calibrated fan temporarily installed in an external doorway. This fan either pressurises or depressurises the building, creating a pressure difference between the inside and outside. Sensors then measure how much air the fan must move to maintain that pressure.
The more air required to maintain pressure, the leakier the building.
A blower door test measures the amount of air leaking through a building envelope. During the test, calibrated fans are used to pressurise or depressurise the building to 50 Pascals (Pa), allowing the total leakage rate to be quantified.
The result can be expressed in different ways depending on the building type and project requirements. Residential projects and standards such as Passive House commonly use Air Changes per Hour at 50 Pascals (ACH50), while commercial projects are typically assessed using air permeability (m³/h/m² @ 50 Pa). ACH is also frequently used by mechanical engineers when discussing ventilation and building pressurisation.
As a general guide:
Air Permeability @ 50 Pa
20 m³/h/m²
Very leaky building (about the same a shed)
10–20 m³/h/m²
Typical construction
5–10 m³/h/m²
Good practice
≤5 m³/h/m²
High-performance building
Blower door testing is typically performed:
As building standards continue to evolve, blower door testing is becoming an increasingly important tool for verifying construction quality and energy performance.
As energy costs rise and government projects demand measurable outcomes, airtightness has become a core performance metric.
Whether you are targeting NABERS ratings, Green Star certification, or standard NCC compliance, getting the details right at the design stage is non-negotiable.
Need airtightness testing for compliance or project verification? Submit the form and our team will reach out to you shortly.
