A blower door test measures how airtight a house is. A calibrated fan depressurizes the house to 50 pascals and measures the air leaking in, reported as air changes per hour at 50 Pa (ACH50). Ontario requires one during construction when a house uses the SB-12 (Ontario's energy efficiency standard for new houses) Performance Path and relies on airtightness better than 3.0 ACH50 (detached) or 3.5 ACH50 (attached) to comply.
Test mid-construction while leaks are still easy to fix, then test at completion for the number your permit and certification need.
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How the test works
A calibrated fan is fitted into an exterior door frame. With windows and doors closed, the fan pulls air out of the house until the inside is 50 pascals below outdoor pressure. The air flowing through the fan equals the air leaking in through the building envelope. Results are reported as:
ACH50: air changes per hour at 50 Pa, the most common measure
NLA or NLR: normalized leakage area or rate, alternatives allowed under SB-12
When Ontario requires one
Under SB-12, a blower door test is required during construction when a house uses the Performance Path and needs airtightness better than 3.0 ACH50 for a detached house, or 3.5 ACH50 for an attached house, to meet the energy efficiency standard. ENERGY STAR for New Homes, R-2000, Canadian Home Builders' Association (CHBA) Net Zero and EnerGuide evaluations include testing as well.
Mid-construction vs final testing
Mid-construction
After the air barrier, windows and penetrations are in, before drywall. Leaks are easy to find with smoke and cheap to seal.
Final
At completion, for the result your permit, energy model or certification needs.
Builder checklist before we arrive
Exterior doors and windows installed and closable
Plumbing traps filled; fireplace dampers and vents closed or sealed as specified
Air barrier complete at rim joists, attic hatch and service penetrations
Ventilation and exhaust openings ready to be temporarily sealed
The building code requires a test during construction when a house uses the SB-12 Performance Path and needs airtightness below 3.0 ACH50 for a detached house, or 3.5 ACH50 for an attached house, to meet the energy standard. ENERGY STAR, R-2000, Net Zero and EnerGuide evaluations also include a test.
What is a good ACH50 result?
Lower is tighter. The target is whatever your energy model or certification assumed; a mid-construction test lets you find and seal leaks before drywall so you meet it.
Should I test before drywall?
Yes, where possible. A mid-construction test finds leaks at the air barrier while they are cheap to fix.
