Most Australian houses are hot for one of three reasons: the roof space is cooking the ceiling, the windows are letting the afternoon sun straight in, or the cooling you have is not doing its job. The fix can be free, or it can be $22,000. Here are seven, from cheapest to dearest, with what each one actually does.
| Aircon service and clean, per unit | $100–$320 |
| Ceiling insulation top-up, per m² | $10–$30 |
| Ceiling insulation, 3-bed home, installed | $1,200–$4,000 |
| Split system 2.5 kW, installed | $1,200–$2,500 |
| Roof painting, single storey | $2,500–$6,000 |
| Retrofit wall insulation, per m² | $25–$70 |
| Ducted, zoned, installed | $12,000–$22,000 |
First, the free ones
Before spending anything: close blinds and curtains on north and west windows before 10am, not when the room is already hot. Open the house up after dark and shut it at dawn. Put ceiling fans on the summer (anticlockwise) setting. Move the fridge away from the wall. If a room is still unbearable after a week of that, the problem is in the building, and that is what the list below is for.
Seven fixes, cheapest first
- Service the aircon you already have
A dirty indoor coil can halve a unit's cooling output. A service cleans it, checks refrigerant and flushes the drain. If the air from the vent is not clearly colder than the room, start here.
$100–$320 - Top up the ceiling insulation
Insulation that has compressed, shifted or was never thick enough lets the roof space heat the ceiling all afternoon. Ceilings in warmer climates want R3.0–R4.0; Melbourne and cooler cities R5.0–R6.0. A top-up over existing batts is the cheapest building fix there is.
$10–$30/m² - Insulate the ceiling properly
If the ceiling has no insulation at all, this is the single biggest change you can make: our guide puts the cut in heating and cooling costs at 20–30%. A three-bedroom home runs $1,200–$4,000 installed.
$1,200–$4,000 - Cool the one room that matters
If the house is fine except for a west-facing bedroom or a kitchen that cooks you at dinner, a 2.5 kW split system for that room is cheaper than whole-house cooling and runs for $100–$180 a summer.
$1,200–$2,500 - Lighten the roof
A dark roof absorbs heat and radiates it into the ceiling cavity for hours after sunset. Painting a single-storey roof in a light or heat-reflective colour costs $2,500–$6,000 and pairs well with ceiling insulation.
$2,500–$6,000 - Insulate the walls
Harder than the ceiling because the walls are closed, so it is done by injection or during a reclad. Worth it on the north and west walls of a weatherboard or brick-veneer house that never cools down at night.
$25–$70/m² - Ducted, zoned cooling
The whole-house answer. Zoning lets you cool bedrooms at night and living areas by day without running the lot. Only sensible after the ceiling is insulated; cooling an uninsulated house is paying to cool the roof.
$12,000–$22,000
Which one is your house?
- Hot all day, worst in late afternoon, stays hot after dark: roof and ceiling. Fixes 2, 3 and 5.
- One or two rooms unbearable, rest of the house fine: window orientation. External shade on those windows, then fix 4.
- Aircon running flat out and the room still warm: fix 1 first, then check whether the unit is the right size for the room.
- Brick house that holds heat for days after a hot spell: fixes 3 and 6, and night-time ventilation.
What to ask the tradie
- Insulation installer: what R-value, is it batts or blown-in, and will you photograph the ceiling space before and after?
- Air conditioning: what size for this room, and is it the right size for the orientation?
- Roof painter: is the coating heat-reflective, and does the quote include cleaning and priming?
- Everyone: is the quote fixed price, and does it include removal of what is there now?
Sam's tipStick your head through the manhole on a hot afternoon. If the roof space is noticeably hotter than outside and you can see ceiling joists between thin or patchy batts, you have found the problem, and it is the second-cheapest fix on this list.
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