Is roof cleaning actually worth it?
Sometimes. Roof cleaning is worth it when moss and lichen are holding moisture against tiles and lifting them, or streaking coated steel like Colorbond — that's growth doing damage, not just looking bad. Where the roof is simply dark or dusty, it's cosmetic. A soft wash also keeps working after the visit, killing the spores a rinse leaves behind.
Moss and lichen are the reason worth having
Moss and lichen aren't dirt. They're living colonies that root into the porous surface of a tile and hold water there long after the rain has stopped. On a tiled roof that means constant damp under and between the tiles, swelling and cracking in the pointing, and clumps heavy enough to lift a tile edge and break the overlap that keeps water out. Lichen is the stubborn one — the flat grey-green crust that etches into the surface. Left alone, it creeps across the whole shaded pitch.
This is the version of roof cleaning that earns its keep. You're not chasing a colour; you're pulling moisture-holding growth off a surface built to shed water fast. A soft wash — low pressure, the right treatment, time to work — kills the colony at the root rather than blasting the tops off and leaving the spores behind. Done properly it keeps working for weeks after the crew has left, which is why the roof stays clean far longer than a single pressure blast ever manages.
Colorbond wants water, not pressure
Coated steel doesn't grow moss the way clay tiles do, but it streaks — tannin run-off, dirt, and lichen spotting that sits on the coating. Here the fix is gentler than people expect. BlueScope's own maintenance bulletin, TB-4, calls for regular fresh-water washing of coated steel, more often near the coast, and explicitly warns against harsh treatment. Salt-laden air across the Eastern Suburbs and Middle Harbour makes that washing matter more, not less — the grime and salt are exactly what shorten a coating's life if they sit.
So the honest answer on a Colorbond roof is: yes, wash it, gently, and on a schedule. The point isn't shine. It's clearing the grime and salt before they do their slow work. High pressure and abrasives do the opposite of what the manufacturer asks for, which is why a soft-wash approach is the right one on steel just as much as on tile. Match the method to the material and the roof keeps doing the job it was made for.
Cosmetic versus protecting: the honest line
The line worth drawing is this: is the growth holding water against the roof, or is the roof just dark? Moss thick enough to sponge water, lichen lifting tile edges, blocked valleys and debris packed into the pitch — that's cleaning that protects the structure. A roof that's simply grey with age, or dusty, or a shade you'd rather it wasn't — that's cosmetic. Both are legitimate reasons to book a clean. It's just fair to know which one you're actually paying for before you do.
The mistake goes both ways. Some homeowners pressure-clean a sound roof every year chasing a colour it will never hold, and wear the surface down doing it. Others ignore a shaded, north-facing pitch furred with moss until a tile slips and the ceiling below stains. The middle path is to look at what's genuinely growing up there. If it holds water and shifts tiles, it's worth doing. If it's only a tone you've gone off, that's your call — not the roof's.
What a wash can't fix, said plainly
Cleaning is not a repair. A soft wash lifts growth and grime; it does not re-bed ridge capping, replace a cracked tile, or rebuild pointing that has already crumbled. If moss has been lifting tiles for years, some of them may need resetting — and a good crew tells you that rather than washing straight over it. Cleaning also won't stop growth returning on a permanently shaded, damp pitch. It will slow it right down, and a treatment that keeps working buys you the longest gap between visits.
That candour matters because the roof is the one surface you can't inspect from the footpath. Access, pitch and the type of growth all change what the job actually involves, which is why roofs aren't a fixed line on a price menu. Anyone quoting a flat roof figure sight unseen is guessing. The useful number is the one that accounts for your roof's size, pitch, growth and access — not an average pulled off the shape of someone else's house down the road.
Get the number, not a guess
Roof work, unlike windows or gutters, is quoted per job — size, pitch, growth, access and material all move the price, so a firm figure comes from describing the actual roof. Schmick's instant quote returns a bookable price in about 60 seconds, and it holds unless the place turns out materially different from what you told it. Bundle the roof with a house soft wash or a gutter clean on the same visit and you save between 5 and 15 per cent for the shared setup and access.
So: worth it when growth is holding moisture and lifting tiles, or streaking coated steel the manufacturer wants kept clean. Optional when it's only a colour you've tired of. Either way, the way to learn what your roof costs is to get the number rather than a guess. If moss on a north-facing pitch is the reason you're reading this, our piece on Colorbond roofs and moss goes deeper on the growth itself.