Have you ever noticed that your Perth home gets cold almost immediately after you turn the reverse-cycle off on a winter evening? Or that the air conditioning seems to run constantly on a hot summer day without ever quite winning the battle against the heat? If either of these sounds familiar, you are experiencing the consequences of a leaky building envelope — and you are paying for it every month on your energy bill.
Air leakage is the single most overlooked factor in residential energy performance in Australia — and Perth is the worst offender in the country. Understanding what it is, what causes it and what can be done about it is one of the most valuable things any Perth homeowner or prospective home builder can do.
Perth is Australia's leakiest
housing market
Research published by Michael Ambrose and Mike Syme found that the average new build home in Perth has an airtightness rating of 25.5 air changes per hour at 50 pascals (ACH@50Pa). To put that in context:
Average new Perth home
Average Hobart home
(Australia's best)
Passive House standard
(certified maximum)
Perth's figure is not only the highest in Australia — it is significantly higher than the maximum allowed in most of Europe and the United States. A Perth home leaks air at roughly 42 times the rate allowed under Passive House certification. This is not a minor inefficiency — it is a fundamental performance failure that no amount of solar panels or high-efficiency appliances can fully compensate for.
"You can think of a leaky home like a very expensive thermal esky with the lid left open. No matter how good the walls are, the uncontrolled air movement undoes most of the work."
What airtightness actually means —
and why Perth homes fail
Airtightness refers to how well a building's envelope — its walls, roof, floor, windows and doors — resists uncontrolled air movement between inside and outside. In a leaky home, air infiltrates through gaps around power points, ceiling penetrations, window and door frames, wall plate connections, exhaust fans and dozens of other small openings. Individually these gaps seem trivial. Together they represent an enormous thermal liability.
In Perth's climate, uncontrolled air infiltration works against comfort in two specific ways. In summer, hot outdoor air pours into the building through every gap, overwhelming the air conditioning system and forcing it to run constantly. In winter — particularly on Perth's cool evenings and mornings — warm indoor air escapes rapidly, making the home feel cold almost immediately after heating is turned off.
Perth's building culture has historically prioritised outdoor living and assumed that homes would be cooled by opening windows and doors. This is a perfectly valid design strategy in a climate with reliable sea breezes — but it has come at the cost of any attention to building envelope airtightness. Perth homes were simply never designed or built to be sealed.
How airtightness is measured —
the blower door test
Airtightness is measured using a blower door test — a fan is temporarily sealed into an external doorway and used to pressurise or depressurise the building to 50 pascals. The rate at which air leaks through the envelope at this pressure is measured and expressed as air changes per hour (ACH@50Pa).
The blower door test is the method used to verify Passive House certification — every certified Passive House must achieve 0.6 ACH@50Pa or better, independently tested and recorded. It is also used during construction on high-performance projects to identify and seal problem areas before they are covered by linings.
A blower door test in action — the standard method for verifying building airtightness
What you can do —
in a new build or an existing home
New build — design for airtightness
Airtightness is most cost-effectively achieved in a new build. An airtight membrane, carefully detailed connections at all penetrations, and construction supervision to ensure continuity of the membrane are the foundations. SIP panel construction, as used on the Oxley House, delivers inherently higher airtightness than conventional timber framing.
New build — specify HRV or ERV
Airtight construction must be combined with mechanical ventilation — specifically a heat or energy recovery ventilation system that provides controlled fresh air without the energy penalty of uncontrolled infiltration. An airtight home without ventilation creates its own problems.
Existing home — find and seal the leaks
In an existing home, a blower door test can identify the major sources of air leakage. Sealing around power points, ceiling penetrations, exhaust fans, window and door frames and roof cavity connections can significantly reduce leakage — often for a relatively modest cost. It won't achieve Passive House performance, but every ACH reduction has a real dollar value.
Aim for a target, not just compliance
NatHERS 7-star compliance does not include any airtightness requirement. A home can achieve 7 stars and still leak at 25+ ACH. If you are building new, set a specific airtightness target — even 5 ACH@50Pa would put a Perth home in the top percentile nationally and deliver meaningful energy savings.
The connection to
indoor air quality
One of the less obvious consequences of a leaky Perth home is the effect on indoor air quality. Uncontrolled air infiltration brings with it outdoor pollutants, allergens, dust, pollen and — for homes near golf courses, busy roads or industrial areas — chemicals and particulates that accumulate indoors. In a standard leaky Perth home there is no filtration of incoming air — whatever is outside simply enters through every gap.
An airtight home with mechanical heat recovery ventilation reverses this completely. All incoming air passes through filters before entering the building. The occupants control what enters their home, and the indoor air quality is consistently clean, filtered and fresh — regardless of what is happening outside.
The bottom line for Perth homeowners: Airtightness is the single highest-leverage improvement available in residential construction — and the one that Perth's building industry has historically paid least attention to. If you are planning a new build, specifying a target airtightness level and designing and building to achieve it is one of the most valuable decisions you can make.
If you would like to understand what airtightness target is achievable on your specific project and what it would cost, our strategy session is the right place to start.