Why Perth roof spaces need help
Runs of 40 °C days
Perth had 11 days above 40 °C in summer 2021 to 22, including six in a row from 18 to 23 January 2022. A closed-up roof space soaks up heat all day and keeps pushing it into the rooms below well into the night.
The Fremantle Doctor
The south-westerly sea breeze is strongest in December and January, and the average 3 pm January wind at Swanbourne is 27.7 km/h. That suits wind-driven whirlybirds in suburbs near the coast on summer afternoons.
Still days inland
Perth Airport reached 46.7 °C on the day of the city's record. Bradford says one powered vent can do the work of several wind-driven ones, which can make sense further from the sea breeze.
Embers in the hills
Any opening in a roof is a way in for embers. Bradford's all-metal WindMaster comes in a BAL version rated up to BAL 40 when installed to spec, so ask for a rated vent if you're in a mapped bushfire area.
Ventilation and insulation do different jobs
Vents let hot, humid air out of the roof space. Insulation slows heat moving through the ceiling into the house. Your Home says roof and ceiling insulation can save 45 percent or more on heating and cooling costs, so check it first. Before anyone adds insulation, AS 3999 requires a licensed electrician's safety check.
Bradford's rule of thumb is one natural vent for every 90 m2 of roof, with four eave vents per roof vent so outside air can replace what goes out. It also says wind-driven vents still move some air on still days, as hot air rises.
On an older Perth home, ASSEA says old roof ventilators and ventilating ridges may be asbestos cement. Have them checked before they're removed.
Questions to ask about roof vents
- How many vents does my roof need, and how did you work that out?
- Whirlybird or powered vent, given how much breeze my street gets?
- Do I have enough eave vents for air to come in?
- How will the vent be flashed so it doesn't leak in winter?
- Is it rated for bushfire areas, and for salt air if I'm near the coast?
What we'd do before next summer
We'd check the ceiling insulation first, because vents alone can only do so much for the rooms below. Then we'd add vents sized for the roof: whirlybirds near the coast where the Doctor blows most afternoons, and a powered vent further inland if the roof space is very hot. Get it done in spring, before the 40 °C days arrive.
Want a roofer to take a look?
Tell us the job and your postcode. We match it with a Find My Roofer certified roofer who specialises in that kind of work, and they call you to quote. Your number goes to them alone.
Tell us your postcode and what's bothering you about the heat. We pass ventilation jobs to one licence-checked roofer in your part of Perth where we have one, and say so straight away if we don't. More on the job is on our roof ventilation page, and the Perth hub covers the rest.