How Do I Prepare for a Blower Door Test in New Zealand?
A blower door test takes about an hour on site. The preparation — what your team does in the days before the tester arrives — determines whether that hour produces a result you can use, or whether you're booking a retest.
This guide is aimed at builders, site supervisors, and project managers working on new builds or significant renovations in New Zealand where an airtightness test is required — whether for Passive House certification, Green Star, H1 energy compliance, or a contract specification. It covers what to do, what not to touch, and how to run a shakedown test before the accredited tester arrives.
The most common cause of a failed or inconclusive blower door test is not a fundamentally leaky building — it's a building that wasn't ready. Temporary sealing, open penetrations, and missing door seals account for the majority of avoidable failures.
What the Test Actually Does
A blower door test (formally: an air permeability test to ISO 9972) pressurises and depressurises the building using a calibrated fan mounted in an external doorframe. By measuring the airflow required to maintain a standard pressure difference of 50 Pascals, the test determines how leaky the building envelope is. The result is expressed as:
- q₅₀ — airflow per unit of envelope area at 50 Pa, in m³/(h·m²) — used for H1 and most NZ/AU compliance pathways
- n₅₀ — air changes per hour at 50 Pa — commonly used for Passive House, where the target is ≤ 0.6 ACH₅₀
- Q₅₀ — total airflow at 50 Pa in m³/h — used for large or commercial buildings
The test measures the whole building envelope as presented on the day. It doesn't know what's intentional and what's an oversight — an open pipe penetration reads the same as a poorly fitted window. This is why preparation matters.
Before the Test: The Preparation Checklist
Work through these in the week before the test. The goal is to present the building as it will perform in occupation — permanently sealed where it should be sealed, with intentional openings temporarily closed for the test.
✅ Envelope Penetrations
- All pipe and cable penetrations through the external envelope (walls, floor, ceiling) are permanently sealed with appropriate sealant or collars — not just stuffed with insulation
- Exhaust fan ducts are sealed at the external termination (tape or a fitted cap) — these are tested closed because they represent an intentional opening that will be controlled by a damper in use
- MVHR or HRV supply and extract terminals are taped over — intentional openings, temporarily closed per ISO 9972 Method 1
- Rangehood duct is sealed at the external louvre
- Any subfloor access hatches are closed and latched
- Letterbox flap is taped if it doesn't close tightly
✅ Windows and Doors
- All windows are fully closed and latched — not just pulled to
- All external doors are closed — the blower door fan replaces one door; all others must be shut
- Internal doors are open so the fan can pressurise the entire building volume
- Bifold and sliding doors are latched at every locking point, not just the handle
- If any window or door hardware is not yet fitted, flag this to the tester in advance
✅ Fireplace and Combustion Appliances
- Wood burner flue damper is fully closed — if it doesn't seal well, stuff and tape it temporarily
- Open fireplaces must be sealed at the throat — a test with an open flue will fail regardless of how well everything else is done
- Unflued gas heaters are noted for the tester — their combustion air opening is an intentional penetration
✅ Building State
- All linings are complete — a blower door test on an unlined building tests the building wrap, not the finished envelope
- Skirting boards are fixed and any gaps at floor-wall junction are sealed
- Ceiling is fully lined and penetrations (downlights, access hatches, exhaust fans) are sealed
- Any obvious visible gaps or cracks in linings or around frames are sealed before the test — the tester is there to measure, not to find your leaks for you
Run a Shakedown Test First
If you're working toward a performance target — Passive House, a Green Star airtightness credit, or a contractual specification — don't wait for the accredited test to find out where you stand. Run a shakedown test earlier in the build, while you can still fix things cheaply.
A shakedown test uses the same blower door equipment but is conducted at a preliminary stage — typically after the airtightness membrane and tapes are complete but before linings go on. The result tells you whether you're tracking toward your target, and more importantly, where the leaks are. With linings off, you can find and fix them in minutes. With linings on, the same fix might mean cutting, patching, and repainting.
BEO includes a preliminary shakedown visit as standard in projects with demanding airtightness targets. It's the single most cost-effective quality assurance step available for a high-performance build.
On the Day: What to Have Ready
- Floor plan and section drawings — the tester needs the internal volume and envelope area to calculate the result. Have these on site or emailed through beforehand.
- Thermal envelope boundary clearly understood — which spaces are inside the tested volume? Garages, subfloor spaces, and unconditioned roof voids are typically outside; confirm with the tester if there's any ambiguity.
- Site access — a key or site supervisor present. The tester cannot complete the test unaccompanied in most cases.
- Weather conditions noted — if it's very windy (sustained gusts over 6 m/s), the test may need to be rescheduled. Extreme wind creates natural pressure fluctuations that interfere with the measurement.
- The certification requirement — let the tester know upfront whether this is for Passive House PHI certification, ATTMA, Green Star, H1 compliance, or a private contract. Different programmes have different reporting requirements.
What to Expect During the Test
The tester mounts the blower door fan in an external door frame — typically the main entry. The fan runs through a series of pressures (usually 10–70 Pa in both pressurisation and depressurisation) and the software fits a curve to the data points to calculate the result at 50 Pa. A full test to ISO 9972 takes approximately 45–60 minutes on site, plus time for preparation and the test report.
During pressurisation, an experienced tester may walk the building with a smoke pencil or anemometer to locate leakage pathways. This is particularly useful if the result is unexpectedly high and you need to identify where the leakage is concentrated before deciding whether to retest.
✓ Seal These for the Test
- Exhaust fan terminations
- MVHR/HRV terminals
- Rangehood duct louvre
- Fireplace flue / damper
- Letterbox flap
- Subfloor hatches
✗ Do Not Seal These
- Trickle vents (if present and permanent)
- Fixed louvre ventilation panels
- Any permanently open combustion air supply
- Anything you cannot replicate in occupied use
The distinction matters: you temporarily seal intentional openings that have closeable dampers or covers in use. You cannot seal permanent openings that will remain open when the building is occupied. The test result must represent a realistic occupied condition.
Common Reasons Tests Come in Higher Than Expected
- Recessed downlights in the ceiling — each one is a direct penetration through the airtightness layer. Use airtight downlight covers or surface-mounted fittings.
- Electrical penetrations — conduits and cables through the top plate of external walls, or through the ceiling into the roof void, are frequently left unsealed.
- Window and door frame perimeter seals — the frame-to-lining junction is often the biggest single leakage area. Air-sealing tape at this joint before linings go on is standard practice in high-performance builds.
- Exhaust fan bodies — even with the external termination sealed, the fan body itself may have gaps where it penetrates the ceiling lining.
- Subfloor junction — in suspended floor construction, the floor-to-wall junction is notoriously difficult to seal and often accounts for a significant proportion of total leakage.
- Attic access hatches — lightweight, unfitted hatches with no compression seal are a common point of significant leakage.
ATTMA-Accredited Airtightness Testing Across New Zealand
BEO Buildingscience provides ATTMA-accredited blower door testing for residential and commercial projects — Passive House, Green Star, H1 compliance, and contract specifications. We offer shakedown testing during construction and final certification testing, with full ISO 9972 reporting.
Airtightness Testing → H1 Energy Modelling →