blower door testing and draft proofing
What Is a Blower Door Test and What Does ACH50 Mean?
A blower door test uses a calibrated fan fitted temporarily into an external doorway to pressurise or depressurise a house. The technician measures the airflow required to hold a 50 Pa pressure difference, then reports the result as ACH50: the number of complete air-volume changes per hour under that test pressure. Lower ACH50 means a tighter building envelope.
In practical terms, the test turns small leaks into detectable air paths. During depressurisation, outdoor air is pulled through ceiling penetrations, cornice gaps, unsealed manholes, downlights, wall-to-ceiling junctions, window reveals and plumbing openings. A smoke pencil, thermal camera and hand-check around suspect areas can then reveal the exact route.
For Perth homes, ACH50 is far more useful than saying a house “feels draughty.” It gives a baseline before work begins and a measurable result after sealing and insulation upgrades are complete.
| Airtightness result | What it commonly indicates | Recommended response |
|---|---|---|
| Above 10 ACH50 | High uncontrolled leakage, often through ceiling and external-envelope junctions | Prioritise a whole-home leak investigation before adding more insulation |
| 5–10 ACH50 | Moderate leakage; common in older Perth homes | Target roof-cavity openings, external doors, exhaust systems and service penetrations |
| Below 5 ACH50 | Good control for a high-performing home | Protect indoor air quality with correctly ducted mechanical exhaust and planned ventilation |
| 0.6 ACH50 or below | Passive House-level airtightness | Requires detailed design, disciplined installation and dedicated ventilation engineering |
A test pressure of 50 Pa does not represent normal daily conditions. It is a repeatable diagnostic condition that makes leak paths measurable and comparable. For a renovation, CeilingPro recommends testing before ceilings are closed where possible, because a service penetration is quickest and least disruptive to seal while it remains accessible.
Why Does Insulation Underperform Without Air Sealing?
Insulation reduces conductive heat flow, but it cannot stop moving air. If cooled indoor air escapes through a ring gap around a recessed fitting or through an unsealed ceiling penetration, warm Perth summer air can replace it continuously. That bypasses the intended thermal resistance of the insulation layer.
The hard reality is simple: a thick layer of ceiling batts over a ceiling full of holes is not a high-performance ceiling. It is insulation installed above an uncontrolled air path.
In our ceiling upgrade work, the most frustrating call-back is not usually “the insulation is too thin.” It is “the air-conditioner still runs all afternoon.” When we inspect the roof cavity, we often find insulation installed neatly between timber ceiling joists while the manhole perimeter, exhaust-fan cut-outs and electrical penetrations remain open.
A well-sealed ceiling plane allows insulation to perform closer to its installed R-value. It also reduces the risk of dust-laden roof air entering the living space, limits hot-air movement from the roof cavity and improves room-to-room temperature stability.
A targeted ceiling air-sealing package can materially reduce cooling-air losses where ceiling leakage is a major pathway. A 30% reduction in cooling-air loss is achievable in leakage-dominated homes only when it is verified through before-and-after testing, not assumed from the number of gaps sealed.
How Does CeilingPro Find Hidden Roof-Cavity Air Leaks?
CeilingPro begins with a blower door test, then maps leakage rather than sealing randomly. The fan creates pressure across the building envelope; technicians use smoke, airflow sensing and roof-cavity inspection to separate genuine leak paths from harmless internal gaps.
The process normally includes:
- Confirm the pressure boundary. We identify whether the ceiling, walls, windows, external doors and subfloor form the effective enclosure of the conditioned area.
- Test at controlled pressure. The blower door fan establishes a stable pressure difference while gauges record airflow and pressure data.
- Trace the ceiling plane. We inspect recessed-light cut-outs, ceiling access panels, duct penetrations, exhaust housings, cornice junctions and top-plate gaps.
- Inspect the roof cavity. This is where visual checks matter. A ceiling penetration may look sealed from below but remain open around a duct, cable bundle or pipe above the plasterboard.
- Seal and retest. The second test determines whether the work changed the result. This avoids paying for “air sealing” that has no measurable effect.
On older homes in Western Australia, common high-leakage areas include evaporative-cooling ceiling outlets, unsealed duct routes, wall cavities that connect into the roof space, open-vented downlights and loose or poorly fitted manholes. On newer homes, leakage is often concentrated at service penetrations and junction details rather than broad construction gaps.
Which Ceiling Penetrations Need Sealing First?
The highest-priority penetrations are those that pass completely through the ceiling air barrier and connect directly with the roof cavity. These include exhaust-fan cut-outs, downlights, ceiling access hatches, air-conditioning ducts, plumbing pipes, electrical cables and open wall cavities at ceiling level.
Start with the largest and most accessible paths. A 125 mm exhaust duct opening with an incomplete seal has more potential impact than several tiny screw holes. Next, focus on repeat details: a home with 20 recessed fittings can have 20 separate leakage points.
The correct material depends on temperature, movement, fire requirements and access:
- Use compatible flexible sealant for small, stable plasterboard-to-frame junctions and service gaps.
- Use purpose-made grommets or collars around cable and pipe penetrations where movement is expected.
- Use appropriately rated covers or enclosures for recessed lighting where clearance, heat and manufacturer requirements allow.
- Use sealed, insulated access hatches for ceiling manholes rather than relying on a loose plasterboard panel.
- Use mechanical duct connections and suitable tape or mastic for duct joints, not generic cloth tape that fails in roof heat.
Never seal a bathroom, laundry or kitchen exhaust so that moisture has nowhere to go. The objective is to stop air leaking between the occupied space and roof cavity while ensuring exhaust air is ducted to the outside, not discharged into the insulation or roof space.
Does Sealing a Roof Cavity Create Moisture Problems?
No—provided the home separates airtightness from ventilation. A sealed ceiling plane prevents moist indoor air entering the roof cavity through uncontrolled gaps. It does not mean blocking designed roof ventilation, closing required external vents or disconnecting extraction systems.
This distinction matters in WA. Perth’s long hot, dry summers create large roof-cavity temperatures, while winter nights and moisture-producing rooms still require sensible condensation control. The ceiling should act as the internal air-control layer; the roof system must still manage outdoor exposure, roof ventilation provisions where required, and moisture movement according to the building’s design.
Common mistakes include:
- Venting a bathroom fan into the roof cavity.
- Pushing loose-fill insulation hard into eaves and blocking ventilation paths.
- Sealing a roof vent because it is mistaken for a ceiling leak.
- Leaving a roof manhole unsealed because “the roof needs to breathe.”
- Installing a powerful exhaust fan without checking whether make-up air and duct discharge are properly managed.
CeilingPro treats roof ventilation and ceiling airtightness as two separate systems. One protects the roof assembly; the other protects conditioned indoor air. Combining them incorrectly can create discomfort, moisture risk and avoidable energy use.
How Should Insulation Be Upgraded After Air Sealing?
Air sealing should occur before insulation is installed, topped up or repositioned. Once batts cover the ceiling plane, each leak becomes slower to find and harder to repair cleanly. This sequencing is particularly important for Perth roof cavities, where summer heat can make extended work above ceilings difficult.
For a practical upgrade, CeilingPro first removes or repositions insulation only where required to inspect penetrations and junctions. After sealing, insulation is reinstated continuously, without crushing batts around ducts, leaving uninsulated edges or creating gaps around manholes.
The most effective insulation layout follows three principles:
- Maintain full coverage across the ceiling plane, including over ceiling joists where the system permits.
- Keep insulation clear of heat-producing fittings, exhaust components and required ventilation routes.
- Build insulated, gasketed access solutions around manholes and service zones rather than leaving a weak thermal and air-leakage point.
Gyprock ceilings need careful handling during retrofit work. Excess pressure from above, poorly supported foot traffic or heavy material piled between ceiling joists can crack joints and create new leakage paths. Experienced crews stage materials on structural members, not on the plasterboard lining.
For homes with aging or contaminated insulation, removal may be the right first step. It provides a clean view of wiring, penetrations, ducting and ceiling damage before new insulation is installed.
Can Blower Door Results Improve a Perth Energy Rating?
Yes. Airtightness affects heating and cooling demand, indoor comfort and the assumptions used in building-performance modelling. A lower measured air-leakage rate can support a more accurate assessment than a generic default assumption, especially for a home designed or renovated for higher performance.
However, airtightness is not a stand-alone energy rating shortcut. The final result also depends on insulation continuity, glazing, orientation, shading, thermal mass, appliance loads, air-conditioning design and ventilation strategy.
For a Perth renovation, the strongest sequence is:
- Establish a blower door baseline.
- Locate the dominant leakage paths.
- Seal the ceiling and external-envelope discontinuities.
- Upgrade insulation without gaps or compression.
- Retest airtightness.
- Use the verified result in energy-performance documentation where applicable.
This approach is more reliable than adding insulation first and hoping the energy model reflects real construction quality. It also gives owners evidence that the upgrade has improved the building envelope rather than merely changing its appearance.
When Should a Perth Home Have a Blower Door Test?
The best time is before finishes conceal the work and again after air-sealing measures are complete. For a new build, arrange a preliminary test once the primary air barrier, windows and external doors are installed but before final linings or insulation make repairs difficult.
For an existing Perth home, schedule testing before an insulation replacement, ceiling repair, major HVAC upgrade or energy-rating assessment. A pre-upgrade test gives a baseline; a post-upgrade test shows whether the work achieved a real reduction in leakage.
Timing also affects site conditions. Avoid treating a single windy, hot afternoon observation as the whole diagnosis. The calibrated test accounts for pressure measurement, but leak tracing is easier when technicians can access the roof cavity safely and use smoke without disruptive cross-breezes.
A pre-winter test can identify cold draughts before heating demand rises. A pre-summer test helps locate the roof-cavity leaks that undermine air-conditioning during Western Australia’s hottest months.
What Does CeilingPro Expert Views Say About Airtightness?
“The ceiling is often the forgotten boundary in a Perth home. Owners can see window gaps and feel draughts at doors, but the biggest leakage route may be above their heads—hidden by insulation and plasterboard. In our experience, the best results come from testing first, sealing the actual pressure boundary, then restoring insulation in a continuous layer. We do not chase a low ACH50 number at the expense of bathroom extraction or roof-space moisture management. The goal is controlled airflow: conditioned air stays inside, exhaust air goes outdoors, and the roof system performs as designed.” — CeilingPro Technical Team
CeilingPro applies this approach across ceiling installation, insulation upgrades, wall partitions and maintenance work in Perth. The company’s integrated workflow helps coordinate ceiling repairs, service access, insulation continuity and final quality checks rather than treating them as unrelated trades.
How Can Homeowners Prepare for a Blower Door Test?
Prepare the home so the test reflects the normal building envelope, not temporary obstructions. Close external windows and doors, open internal doors unless instructed otherwise, and ensure technicians can access ceiling manholes, external doors and relevant service areas.
Before the appointment, make a list of known comfort problems: a bedroom that overheats, a bathroom ceiling that stains, a living room with dusty air around downlights or a hallway that feels draughty when the air-conditioner runs. These observations help direct the inspection.
Do not tape over obvious leaks immediately before testing if the purpose is diagnosis. That can hide the pathways that need durable repairs. If the purpose is final verification, confirm with CeilingPro which openings should remain in their normal operating state and which systems must be temporarily closed for the test.
What Are the Most Common Blower Door Testing Questions?
How long does a blower door test take?
A typical detached house test often takes one to three hours, depending on size, access, the number of zones and whether leak tracing is included. A simple numerical test is quicker than a full diagnostic inspection with roof-cavity checks and before-and-after verification.
Can I stay in the house during testing?
Usually, yes. The pressure difference is modest, but technicians may ask occupants to avoid opening external doors, operating exhaust fans or changing window positions during the test. Pets should be secured because the test-door assembly occupies an external doorway.
Are open-vented downlights a major problem?
They can be. They interrupt insulation continuity and may create direct air paths to the roof cavity. Each fitting should be assessed for electrical safety, heat clearance, insulation compatibility and a compliant airtight enclosure or replacement option.
Can I seal every gap myself?
Homeowners can install door seals and address simple accessible gaps, but ceiling penetrations, recessed fittings, exhaust ducts and electrical openings require careful treatment. Incorrect sealing can create fire, condensation or ventilation problems. Use qualified trades where electrical or roof-space safety is involved.
Will draught proofing make indoor air unhealthy?
Not if the home has planned ventilation. Airtightness removes uncontrolled leakage; it does not eliminate the need for bathroom, kitchen and laundry extraction. As a home becomes tighter, reliable ducted exhaust and appropriate fresh-air planning become more important.
What Should You Do Next?
Start with measurement, not guesswork. A blower door test identifies whether the greatest comfort problem is air leakage, missing insulation, poor ducting, solar gain or a combination of these factors. From there, prioritise the ceiling plane: manholes, downlights, exhaust fans, duct penetrations and wall-to-ceiling junctions.
For Perth and wider WA homes, the best-performing upgrade sequence is clear: test the building, seal verified leakage paths, preserve correct roof and exhaust ventilation, install continuous insulation, then retest. CeilingPro can coordinate ceiling repairs, air-sealing details and insulation upgrades so the finished system delivers measurable comfort rather than just more material in the roof cavity.
