Why standard double-brick homes struggle in Perth's climate

It is 8 pm on a February evening. The sun set an hour ago. The air conditioning has been running since midday. But the house is still hot. The walls are warm to the touch. The bedroom will not cool down until well past midnight, and even then it will be the air conditioning doing the work, not the house itself.

If you have lived in a standard double-brick home in Perth, you know this feeling. You might assume it is just what summer is like. But it is not bad luck and it is not inevitable. It is physics. And once you understand the physics, the solution becomes obvious.

The pizza oven effect

Standard double-brick construction in Perth follows a consistent pattern: two layers of brick with a cavity between them, plaster on the inside, and a specification pushed no further than the code requires. It is the dominant construction method in Western Australia and has been for decades.

A note on what this article is about. The problem is not brick. It is what happens when a double-brick home is built to the minimum and the design is left to do none of the work. Norde builds double brick, and builds it to 8 stars and above. The difference is entirely in the design decisions described below.

Here is what happens during a Perth summer day. The temperature reaches 35 degrees or more. The outer brick wall faces the sun and begins absorbing heat. Brick is dense and heavy, which makes it very effective at storing thermal energy. By mid-afternoon, the outer leaf of brick is saturated with heat.

That heat then migrates inward. It passes through the cavity, through the insulation (which slows the transfer but does not stop it) and into the inner leaf of brick. By late afternoon, the inner brick wall is warm. By early evening, it is radiating that stored heat directly into your living space.

Your walls have become a thermal battery. They spent the day absorbing heat you do not want, and they release it into your home precisely when you need cooling most. The air conditioning runs harder. Your energy bill climbs. And the house does not feel comfortable until the early hours of the morning, when the thermal mass has finally discharged.

The inner brick radiates heat into your living space through the evening and into the night. Your air conditioning is not fighting the outside temperature. It is fighting your own walls.

This is not a design flaw in the traditional sense. Double-brick construction was developed for cold European climates, where retaining heat inside the home is exactly what you want. A heavy masonry wall that absorbs daytime warmth and releases it slowly through a cold evening is a genuine advantage in London or Berlin. Perth's climate presents the opposite problem. We have mild winters and long, hot summers. The thermal mass works in reverse.

It is the heat the walls collect that matters

Two details make this worse than it first appears. The cavity insulation slows the heat crossing the gap, but the two leaves of brick are also physically connected, by metal wall ties across the cavity and by masonry at openings and junctions. Those connections act as thermal bridges: direct conductive paths that carry heat, and in winter cold, straight from the outer leaf to the inner one, partly bypassing the insulation. So even with a well-insulated cavity, the bridges keep feeding the inner brick.

The deeper issue is which heat the mass collects. Thermal mass is slow to release whatever it has stored, so what matters is controlling when it heats up. In a home where the outer wall bakes in the afternoon sun with nothing sized to shade it, the mass charges with exactly the summer heat you do not want and gives it back overnight. A reverse brick veneer wall keeps the mass inside the insulated envelope, where its heating can be controlled: warmed by low winter sun through north-facing glass, and shaded from the high summer sun. Same physics, opposite result.

Why most Perth builders still build this way

Double brick has been the default residential construction method in WA for decades. The trades are set up for it. The supply chains are optimised for it. Building codes allow it. Most project home builders have their entire business model structured around double-brick construction, from their standard designs to their subcontractor relationships.

It is not that builders do not know about alternatives. Double brick is familiar, efficient to build at scale, durable, and the most affordable way to build in Perth. Those are real advantages, and they are why it remains the right answer for plenty of briefs. The problem is not the method. It is building to the minimum and calling it done.

The minimum NCC energy rating of 7 stars is easily met with double brick. But 7 stars is a low bar. It represents the minimum standard, not a target for genuine comfort, and most homes in Perth stop exactly there.

Double brick, done properly

This is the part most articles on the subject leave out. A double-brick home is not condemned to 7 stars. With the orientation right, high-performance double glazing and an insulated cavity, double brick reaches 8 stars and above. We build them.

What separates a good double-brick home from a poor one is not the bricks. It is whether the design does any work. North-facing living areas. Eaves sized for Perth's sun angles rather than drawn to a standard detail. Glazing specified per elevation instead of one window type throughout. An insulated cavity rather than an empty one. Skip those and you get the 7-star box. Make them and you get a home that performs, at the most affordable price of any method we offer.

Where reverse brick veneer pulls ahead is at the top of the scale. Putting continuous insulation outside a large internal mass is what takes a home from performing well to barely needing mechanical heating or cooling at all, which is the 9 to 10 star range. Both are good outcomes. They sit at different points on the same scale, and at different price points.

What the numbers actually show

A minimum-specification double-brick home in Perth sits at or just above the 7-star floor. That is the reality of the vast majority of new homes being built here right now, and it is a choice rather than a limit of the material.

The difference between a 7-star home and a 9-star home is not incremental. Under the official NatHERS star bands for Perth, a 7-star home is allowed 52 MJ/m²/yr of heating and cooling and a 9-star home 17. That is two thirds less energy for the same comfort. It is a fundamentally different level of thermal performance, and you feel it every day you live in the house.

The difference between 7 stars and 10 stars is a different order of magnitude entirely. A 10-star home requires almost no mechanical heating or cooling to maintain comfortable temperatures year-round. The house does the work itself.

Norde Homes builds consistently in the 9 to 10 star range. These are not theoretical projections. They are assessed NatHERS ratings on completed homes in Perth's climate zone. The Woodlands project achieved a 10-star rating. Hazelmere achieved 9.1 stars. Palmyra achieved 8.4 stars on a constrained block with a difficult orientation.

What this means for running costs

Consider a 7-star home in Perth. On a 38-degree February day, the air conditioning might run for 10 to 12 hours to hold a comfortable indoor temperature. Multiply that across a summer and the demand is substantial. Under the NatHERS star bands for Perth, a 7-star home is allowed up to 52 MJ/m²/yr of heating and cooling.

A 9-star home on the same block, built with passive solar orientation and thermal mass inside the insulation, might use air conditioning for 2 to 3 hours on the same day. Its allowance is 17 MJ/m²/yr, two thirds less energy for the same comfort. That gap repeats every year for the life of the building, and widens in value as energy prices rise.

The upfront cost difference between the two approaches is typically recovered within 7 to 10 years through lower running costs alone, without accounting for the comfort difference or the resale value of a high-performance home.

The alternative: putting insulation where it matters

The most effective alternative to standard double brick for Perth's climate is reverse brick veneer. The concept is straightforward: flip the construction. Put the brick on the inside of the wall and the insulation on the outside.

When you do this, something important changes. The internal brick wall is no longer exposed to the sun. It sits behind a continuous layer of external insulation that blocks outside heat from reaching the thermal mass. The brick still functions as a thermal battery, but now it is working for you instead of against you.

During winter, the internal brick absorbs warmth from inside the home during the day, from sunlight entering through north-facing windows, and releases it slowly through the evening. The home stays warm without the heater running. During summer, the external insulation prevents outside heat from reaching the brick. The thermal mass stays cool and helps stabilise indoor temperatures.

Combined with passive solar orientation, the result is a home that works with Perth's climate instead of against it. North-facing living areas capture the low winter sun. Eaves and shading block the high summer sun. Cross-ventilation pulls the Fremantle Doctor through the home on summer evenings. The house becomes a system where every element contributes to comfort.

Can you fix an existing double-brick home?

The honest answer is: not easily. The fundamental issue is the wall construction itself, and you cannot change that after the home is built. The slab is poured, the walls are up, the orientation is fixed.

There are improvements you can make. External insulation cladding can reduce heat transfer through the walls. Upgrading to double-glazed windows with low-E coatings makes a measurable difference. Adding or improving roof and ceiling insulation is one of the most cost-effective retrofits available. Shade structures on the west and north faces help reduce direct solar gain.

But you cannot add internal thermal mass to a finished home. You cannot change the orientation after the slab is poured. You cannot retrofit the continuous insulation envelope that makes reverse brick veneer effective. For existing homes, targeted renovation can improve comfort noticeably, but it will not match a purpose-built design.

If you are building new, you have the opportunity to get it right from the start. The cost of doing it well at the design stage is a fraction of trying to fix it later.

Five signs your home is fighting Perth's climate

You do not need a NatHERS assessment to recognise the symptoms. If your home is working against the climate rather than with it, the signs are hard to miss.

The first is rooms that are still hot at 8 pm even with the air conditioning running. If the AC has been on all afternoon and the house is still warm in the evening, the walls are releasing stored heat faster than the system can remove it.

The second is energy bills that spike dramatically in January and February. A home that performs well should not show a radical difference between its winter and summer energy costs. If your summer bills are two or three times your winter bills, the building envelope is not doing its job.

The third is bedrooms that do not cool down until after midnight. This is the thermal mass problem at its most noticeable. The walls in a west-facing or north-facing bedroom absorb heat all afternoon and radiate it through the evening. You lie in bed and the room feels warm even though the air conditioning is running.

The fourth is a west side of the house that becomes unusable in summer afternoons. If you avoid certain rooms between 2 pm and sunset during summer, the glazing and wall construction on that elevation are not managing solar gain.

The fifth is closing curtains and blinds by 10 am to keep the heat out. If your response to a summer morning is to seal the house and rely entirely on mechanical cooling, the home is not designed for the climate it sits in.