Can You Fail a Blower Door Test?
“Pass” and “fail” depend entirely on what target you're being tested against — here's how that works.
Homeowners and builders booking a blower door test often ask a version of the same question: “what happens if I fail?” The honest answer is that there’s no single universal pass mark. Whether a result counts as a pass or a fail depends entirely on what target applies to your project — and in many cases, there’s no formal target at all.
14 min read
Key takeaways
- There is no single national “pass” or “fail” ACH50 number in Australia. What counts as passing depends on the specific target: Passive House certification, a builder's specification, or a project-specific goal.
- NCC 2022 doesn't set a maximum ACH50 — testing under 5 ACH50 triggers a mechanical ventilation requirement, not a “fail”.
- Passive House certification requires ≤0.6 ACH50 — the closest thing to a true pass/fail line in Australian high-performance building.
- Most “failed” results are caused by a handful of common, findable and fixable leakage areas.
- If a target is missed, the usual next step is leak-hunting, targeted sealing, and a retest — not a rebuild.
Jump to a section
1. What does “passing” a blower door test actually mean?
A blower door test itself doesn’t pass or fail anything — it simply measures a building’s airtightness and reports a result, expressed as ACH50. Whether that result counts as a “pass” depends entirely on whether there was a target to measure it against.
Three very different reasons to test
A blower door test might be run to certify Passive House compliance (strict pass/fail), to verify a contractual specification (pass/fail against a written number), or purely diagnostically on an existing home with mould or comfort complaints (no pass/fail at all — just information to guide repairs).
2. There’s no universal pass mark
Passive House certification
Fixed target? Yes — ≤0.6 ACH50, fixed and non-negotiable
If missed: Certification withheld until remediation and a passing retest
NCC 2022 (general compliance)
Fixed target? No maximum ACH50 to “pass”
If missed: Testing under 5 ACH50 triggers a mechanical ventilation requirement — not a fail
Builder / contract specification
Fixed target? Sometimes — if written into the contract
If missed: A specification non-compliance, handled between builder and client
Existing home diagnostic testing
Fixed target? No
If missed: Nothing to fail — the test documents performance and locates leaks
The takeaway: before you can know whether a result “passed,” you need to know what it was being tested against. This should be settled before the test, not after.
3. Passive House targets
Passive House is the one context in Australian high-performance building where there’s a genuinely fixed pass/fail line: ≤0.6 ACH50, tested per Passive House Institute protocol. A Passive House project that tests above 0.6 ACH50 at final test simply cannot be certified until further sealing work brings it under the threshold.
Because the margin for error is so small, Passive House projects almost always include a mid-construction (pre-lining) test as standard practice — see preparing for a blower door test.
HiPer Haus field note
HiPer Haus has supplied and commissioned MVHR for several certified and near-certified Passive House projects in South Australia, including a Certified Passivhaus at Thebarton and the Passivhaus Plus display home at Mount Barker (both built by Enduro Builders).
4. Builder and contract specifications
Many project specifications now nominate a specific ACH50 target as a measurable performance requirement — independent of any regulatory requirement. In this context, “failing” means the tested result doesn’t meet the number written into the contract.
Reading the fine print
“Best endeavours to achieve ≤5 ACH50” and “shall achieve ≤5 ACH50, tested and documented at handover” are very different commitments. If airtightness performance matters to you, ask which wording applies to your contract.
5. Existing homes — testing without a target
For most existing homes, there’s usually no formal target at all. The test is run diagnostically: to establish a baseline ACH50, and to physically locate specific leakage paths using a smoke pencil or thermal camera. The useful output isn’t a pass/fail verdict — it’s a prioritised list of leaks to address.
6. Common leakage areas found during testing
Downlights
Direct penetration into the roof space, often with gaps around the fitting
Typical fix: IC-rated, gasketed downlights or airtight cover boxes
Exhaust fans
Ducting and ceiling penetrations often poorly sealed; leaky backdraught dampers
Typical fix: Properly sealed ducting, quality dampers, correct external termination
Cornices and skirtings
Gaps between plasterboard and structure at ceiling/wall and wall/floor junctions
Typical fix: Caulking or tape at the airtight layer before fitting
Window and door reveals
Gaps between frame and structure where wrap wasn't properly taped
Typical fix: Correctly taped membrane laps around every frame
Service penetrations
Cables and pipes passing through the air barrier unsealed
Typical fix: Grommets, sealant or purpose-made airtight sleeves
Roof access hatches
Often just a lid resting in an opening, no gasket
Typical fix: Gasketed, latching hatch covers
Evaporative cooling ducts
Large uninsulated, unsealed ducts direct to outside air
Typical fix: Sealed, insulated ducting with a well-fitted damper
HiPer Haus field note
On a pre-renovation test of an existing home at Nairne, the combined leakage measured 1,149 cm² (0.115 m²) — equivalent to a single round hole about 38 cm across, noticeably larger than an A4 sheet of paper (roughly 624 cm²). That’s a real, documented result on an untreated existing home.
Related calculators
7. What happens if you don’t meet your target
- 1Depressurise and leak-hunt: the tester uses a smoke pencil (and sometimes a thermal camera) to physically locate where air is entering.
- 2Prioritise and seal: leaks are ranked by size and accessibility, then sealed with tape, sealant, or gaskets appropriate to the detail.
- 3Retest: once sealing work is complete, the blower door test is repeated to confirm the target has been met.
The cost and disruption depends heavily on when the first test happened. A pre-lining test that finds leaks while the airtight layer is still exposed is quick and cheap to fix. A final test at practical completion is considerably more disruptive and expensive to remediate.
Want leaks found while they’re still cheap to fix?
Book a pre-lining test →8. Retesting — process, timing and cost
Retesting is common, not exceptional — particularly on Passive House projects, where hitting ≤0.6 ACH50 on the first attempt is achievable but not guaranteed. Where possible, schedule the retest soon after remediation, while the trades who did the sealing work are still engaged.
9. What a blower door test report includes
A proper report includes the headline ACH50 result, the raw Q50 airflow figure and building volume used, the test direction(s), building details, conditions on the day, a leakage summary with photos, and — for Passive House or NCC-relevant testing — certifier-ready documentation. Ask for this level of detail up front.
Frequently asked questions
Is there a legal minimum ACH50 a new home in Australia must achieve?
No. NCC 2022 doesn't set a maximum ACH50 a home must pass. It requires mechanical ventilation meeting a minimum calculated airflow rate once a home tests under 5 ACH50.
What ACH50 do I need for Passive House certification?
0.6 ACH50 or lower, tested per Passive House Institute protocol. This is a fixed requirement with no flexibility.
Can a blower door test damage my home?
No, the test uses moderate, controlled pressures well within what buildings are designed to withstand.
What if my new home tests above 5 ACH50, do I fail?
No, there is no fail at 5 ACH50 under general NCC pathways. It means mechanical ventilation meeting the minimum calculated airflow rate is required.
How much does it cost to fix a leaky result?
It depends on what's found and when. Leaks found pre-lining are inexpensive to seal; leaks found at final test after linings are up cost more to fix.
Should I test during construction or just at the end?
Both, ideally. A pre-lining test lets leaks be found and fixed cheaply; a final test documents the completed result.
Can an existing home fail a blower door test?
Not formally, unless a specific target has been set. Most existing-home testing is diagnostic rather than pass or fail.
Does my builder have to guarantee a specific ACH50?
Only if it's written into the contract or specification.
What are the most common reasons homes miss their target?
Downlights, exhaust fan ducting, cornice and skirting junctions, window and door reveal sealing, and service penetrations.
Can I seal leaks myself before a retest?
For accessible leaks before lining, yes in consultation with your builder. For leaks behind finished linings, professional remediation is usually required.
How long does a retest take?
Similar to the original test, typically a couple of hours on site, varying with building size and number of leaks being verified.
Does a fail affect my home insurance or resale value?
The result itself isn't reported to insurers, but unresolved moisture or mould issues stemming from inadequate ventilation could be relevant at resale inspection.
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Booking a test and want to understand your target first?
Book a blower door test with HiPer Haus, or get in touch to discuss the right airtightness target for your project.
Written by
Jonathen HindryFounder of HiPer Haus. 25+ year plumber turned Certified Passive House Tradesperson — blower door testing, MVHR design and heat pump hot water across Adelaide and South Australia.
