What grows on Perth roofs, and where
Rain climbs toward the scarp
Rottnest Island averages 564.5 mm of rain a year, Perth Metro 723.9 mm, Jandakot 811.5 mm and Bickley, up in the Perth Hills, 1,096.1 mm. A roof under trees in the hills is likely to stay damp far longer than one on an open, sunny block near the coast.
Terracotta grows more
Monier says moss and lichen grow more often on terracotta, especially unglazed, than on concrete tiles, but only on the surface, without harming the tile. Perth's Federation bungalows had terracotta roofs, so older homes may see more of it.
Asbestos-era roofs
The City of Cockburn notes asbestos-cement shingles on Inter-War and post-war Perth houses. According to ASSEA, water-blasting an asbestos roof has sent fibres onto neighbouring properties, roads and into stormwater, and some clean-ups have run into hundreds of thousands of dollars.
No pressure cleaning on a possible asbestos roof
WA law bans cleaning asbestos materials with high-pressure water, and WA Health says old asbestos cement roofs can be unsafe to walk on. If your home was built or renovated before 1990 and the roof is grey sheeting or shingles, treat it as possible asbestos until a lab test says otherwise. Try our asbestos checker first.
Pressure, chemicals, or a gentler clean?
Pressure cleaning is what most people picture, but Monier, which makes concrete and terracotta tiles, strongly advises against pressure washers on its tiles because they can damage them, and recommends a professional roof cleaner instead. Ask any cleaner how they protect the tile surface.
Many roofers use a chemical moss treatment, sometimes with low-pressure water, which kills growth without blasting the surface. Because Monier says moss doesn't affect a tile's strength, a clean is mostly about looks, keeping valleys and gutters flowing, or preparing for a coating.
What to ask a Perth roof cleaner
- Have you checked my roof isn't asbestos cement?
- Which method will you use on my tiles, and why that one?
- How will you keep the runoff out of my gutters and downpipes?
- Will you photograph any cracked tiles or loose ridge caps you find?
- Is clearing the gutters afterwards in the price?
What you can do, and what's for a professional
You can
- Trim branches that shade the roof, from the ground
- Look from the ground or a window for green or black patches
- Ask a cleaner to look if growth is spreading into valleys
Leave to a roofer
- Any cleaning on the roof itself
- Chemical moss and lichen treatments
- Anything on a roof that might be asbestos cement
Our honest view
We'd only pay for a stand-alone clean if the roof is sound and you want it looking better, or you're selling. If a restoration or repaint is on the cards in the next year or so, we'd fold the clean into that job rather than pay for it twice. And in the hills, trimming the trees that shade the roof does more than any single clean.
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 the roof's made of, if you know. We'll pass the job to one licence-checked local roofer where we have one for your area, and say so straight away if we don't. See roof cleaning for the general guide, or go back to Perth.