What Brisbane's weather does to a roof surface
Humid air and frequent rain
Summer dew points in Brisbane average about 20 °C, and afternoon humidity in the city centre averages 52%. Slopes that face away from the sun or sit under trees stay damp for long stretches, which is what moss and lichen need.
Terracotta grows more
Monier says moss and lichen turn up more often on terracotta than on concrete tiles, especially unglazed terracotta. It sits on the surface and doesn't weaken the tile, but it holds moisture and dirt and has to go before any coating.
Fibro roofs: water-blasting is illegal
If the house was built before 1990, the roof could be asbestos cement. Queensland makes it illegal to use a high-pressure water blaster on asbestos cement roofs, fences and walls, with fines of up to $10,000 plus the cost of cleaning up. ASSEA says blasted fibres have spread to neighbours' yards, footpaths, roads and stormwater.
Salt where the rain doesn't reach
Rain keeps most metal roofs clean, but BlueScope says areas it can't reach, like under eaves and the underside of gutters, should be washed at least six-monthly, or three-monthly near the coast where there's salt spray. On a Brisbane waterfront home, that's a regular job.
How a roof should be cleaned
On concrete or terracotta tiles, Monier strongly advises against pressure washers because they can damage the tiles, and recommends a professional roof cleaner. Ask whether they'll use a low-pressure wash or a treatment that kills the growth instead.
On Colorbond, BlueScope's method is household detergent and water with a soft brush or mop, then a fresh-water rinse. It warns against abrasive or solvent cleaners like turpentine, kerosene or paint thinners. On an asbestos cement roof, Queensland's asbestos site suggests a fungicide and sealant rather than any cleaning.
Questions for a Brisbane roof cleaner
- What's my roof made of, and could it be asbestos cement?
- Which method will you use on my roof, and why?
- Is the treatment safe for my garden, pets and rainwater tank?
- If you crack a tile, will you replace it at no charge?
- Is this a clean only, or the first stage of a restoration?
Our advice
We'd clean a roof gently or not at all. On tiles, that means a treatment or low-pressure wash rather than a blaster, and on a possible fibro roof, testing first and a fungicide and sealant if it's asbestos. If the clean is the first step towards painting, get both quoted together. The national roof cleaning page and the Brisbane hub have more.
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.