What your airtightness number actually means

A blower door test gives you a measured leakage rate under controlled pressure conditions.

It’s valuable because it’s measurable—but it’s not the whole story.

The useful question is not whether one number is “good” in isolation. It is what building boundary was tested, why the test was run, what conditions or adjacent spaces affected it, and which decision the result needs to support.

Three ways to use airtightness results

1) Benchmarking

A score creates a baseline and can help track improvement when the building boundary and test context are comparable. Record the test stage and assumptions with the result.

2) Diagnostics

When used in diagnostic mode, pressure can support smoke, thermal, or other observations that help identify where air is moving. That work must be part of the scope; a number alone does not locate leakage.

3) Planning

Airtightness targets can guide trade sequencing and mid-construction checks. Testing while details remain accessible can also help the team correct issues before finishes restrict the work.

What the number doesn’t tell you by itself

• where leaks are located (unless diagnostics are done)
• whether comfort issues are caused by leakage vs distribution vs ventilation
• how attached geometry affects interpretation (multi-unit context matters)

Questions to keep with the result

• What area and building boundary were included?
• Was the goal documentation, benchmarking, diagnostics, or verification?
• Which assumptions or access limits affect interpretation?
• For an attached building, how were adjacent units and common spaces handled?
• If a target was supplied, who owns that requirement and at which project stage?

Choosing the next step

If the result is for documentation, a clear test summary may be enough. If the decision is where to correct a draft or envelope issue, ask for diagnostic observations. If the result will be compared with another test, keep the boundary, stage, and conditions with both records.

Program, label, and permit decisions remain with the applicable organization. Airtightness testing supplies measurement and context; it does not promise eligibility, approval, or a particular building outcome.