Why moss picks your roof
Moss grows where a roof stays damp: on south-facing slopes, which get the least sun in Australia, under trees, and anywhere leaves collect, like valleys and the back of a chimney.
The roof material matters too. Monier says moss and lichen grow more often on terracotta than on concrete tiles, especially unglazed terracotta. Once growth starts, it traps more dirt and water, and the patch spreads.
Lichen is the flat, crusty growth, often grey, yellow or orange. It holds on harder than moss and can leave marks behind even after it's dead.
Why it's worth removing
Not because it eats the tiles. Monier says the growth sits only on the surface and doesn't affect a tile's integrity.
The trouble is where it ends up. Clumps break off and wash into gutters, valleys and downpipes, where they block the flow and can make water overflow into the eaves. Thick moss along tile overlaps can also dam water so it finds a way underneath. Monier suggests clearing gutters, downpipes and valleys at least once a year, or twice in tree-lined areas.
How a roofer clears moss and lichen
Check what's underneath
First they confirm the roof type, look for cracked tiles hidden under the growth, and rule out asbestos cement.
Treat the growth
A moss and lichen killer goes on, usually at low pressure. Some roofers then leave it for days or weeks so the growth dies back and lets go.
Remove it gently
Dead growth is rinsed or brushed off. Monier warns pressure washers risk damaging tiles, so a hard blast shouldn't be the default.
Clear the drainage
Gutters, valleys and downpipes are emptied of everything that came off the roof.
Slow the comeback
A follow-up treatment and trimming nearby trees both help keep regrowth down.
Lichen on an old fibro roof
Old asbestos cement roofs often carry heavy lichen, and it's tempting to scrub or hose it off. Don't. ASSEA, the national asbestos agency, says never to use high-pressure water or abrasive methods on asbestos cement roofs, and Queensland's asbestos authority recommends applying a fungicide and sealant instead of cleaning them. Have the roof identified first, and read can you paint an asbestos roof? before agreeing to anything.
What's safe for you, and what isn't
You can
- Cut back branches that shade the roof or drop leaves on it
- Keep gutters flowing, if you can reach them safely from a ladder
- Notice which parts of the roof grow moss first, and tell the roofer
- Point out rainwater tanks, ponds and veggie patches below the roof, so the runoff is managed
Leave to a roofer
- Applying moss killer up top, which makes the surface slippery
- Rinsing, brushing or any pressure cleaning
- Fitting anything to the roof to slow regrowth
- Assessing an old roof that might be asbestos
If it were our house
We'd tackle the cause as well as the moss: trim the trees that shade the roof and keep the gutters clear. Then we'd ask for a kill-first treatment and a gentle wash rather than a hard pressure clean. And we'd ask the roofer to photograph any cracked tiles they find under the growth, because that's the part that actually lets water in.
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.