Signs Your Roof Needs Cleaning (Melbourne Guide)

Roofs fail slowly and quietly, and because nobody looks at their own roof from the right angle, the signs get missed until water is coming in. The good news is that a roof tells you well in advance when it needs attention, and most of the signs can be read from the street or from the gutters — no ladder required. Here is what to look for on a Melbourne roof, and what each sign actually means.

The signs you can see from the street

Walk out to the nature strip and look at the whole roof, face by face. Dark streaks running down the slope are usually algae following the path water takes off the roof — they show up first on the face that gets the least sun. Green patches or lines in the tile overlaps are moss, which grows exactly where moisture lingers. Pale grey, white or orange discs that look crusted onto the tile are lichen, which bonds to the surface and spreads slowly outward year on year.

Then step back and compare the faces of the roof against each other. A healthy roof looks consistent; an ageing one looks patchy, because growth follows shade and moisture rather than spreading evenly. In Melbourne the south-facing side and any face under tree cover will always go first — if that face is visibly green or streaked while the north face still looks clean, the roof is telling you where it is losing the battle.

The signs waiting in the gutters

The gutters are the roof’s drainage record, and they collect the evidence. Gutters that keep filling with coarse grit are catching the surface of concrete tiles as it erodes — sustained dampness under moss and lichen accelerates that erosion, and the grit is the result. Clumps of moss in the gutters or at downpipe outlets mean growth upslope is thick enough to break off. Litter lines packed into the roof valleys act as little dams, pushing water sideways under the tiles during heavy rain — which is how a technically sound roof still manages to leak.

After a decent rain, look at what the roof sheds. Dirty, tea-coloured streaks down external walls below the roofline, or stained runoff across paths under the eaves, mean the water is washing through built-up grime and growth on its way down. Clean roofs shed clean water. Downpipes tell the same story from below: if what splashes out at the bottom is brown and gritty, that material started its journey on the tiles.

What the growth is actually doing up there

It would be fair to ask whether any of this matters beyond appearance. It does, because the growth changes how the roof handles water. Moss is absorbent — it holds rain against the tile surface for days, where a clean tile would have shed and dried within hours. Growth in the overlaps interferes with the way tiles are designed to channel water, and thick moss can hold enough material to lift tiles slightly and wick moisture where it should never reach. Lichen bonds chemically to the surface; left long enough, it leaves permanent marks even after removal.

On top of the water handling, there is the erosion issue. Concrete tiles rely on their finished surface; constant damp under a blanket of growth wears that surface away faster, which shortens the life of the roof itself — not just its looks.

Why Melbourne roofs go green faster than they should

Melbourne gives roof growth everything it wants: a long, damp, mild winter, cool shoulder seasons, heavy dew, and mature tree cover across most established suburbs. Any roof face that stays shaded through the middle of the day dries slowly, and slow drying is the whole game for moss and algae. This is why roof condition varies so much between suburbs and even between neighbouring houses — the house under the oaks and the house in open sun are living different lives.

It also means timing matters. Growth does most of its expanding through the wet months, so a roof checked in spring shows you honestly what winter added. Storms deserve their own check: after strong winds, a quick look from the street for slipped or cracked tiles, dislodged ridge capping and fresh debris in the valleys catches damage while it is still a small repair. And homes with solar panels have one more reason to care — the same grime and lichen that colonises tiles builds up on and around panels, and the runoff from a dirty roof streaks across them.

What to do when the signs add up

If your roof is showing several of these signs, the fix is a proper roof clean — and the method matters as much as the decision. Roof cleaning done properly uses low-pressure washing and treatments that kill moss, algae and lichen at the root, rather than a high-pressure blast that strips tile surfaces, dislodges pointing and drives water under the overlaps. Treating the growth is what keeps the roof clean afterwards; blasting it off leaves live spores in the surface and the green comes straight back.

It is also a job to keep off your own ladder. Wet, mossy tiles are treacherous underfoot, and roof work without proper access equipment is one of the most common ways home maintenance goes badly wrong. A professional crew has the access gear, the right pressure equipment and the treatments — and while they are up there, they can deal with the gutter cleaning and valley clearing that the same debris has usually made necessary.

The roof is the largest single surface protecting your home, and it is the one you look at least. Reading these signs once a year — from the street, from the gutters, after rain — is enough to catch the slide early, while a clean is still all it needs.

Frequently asked questions

Why is the south side of my roof so much worse than the rest?

Because in Melbourne the south face gets the least direct sun, so it stays damp longest after rain and dew. Moss, algae and lichen need sustained moisture, and the shaded face gives it to them. It is completely normal for one face of a roof to look years older than the others — and it is the face to check when you are deciding whether a clean is due.

Is moss on a roof actually harmful, or just ugly?

It is harmful over time. Moss holds water against the tile like a wet sponge, keeps the surface damp for days after rain, and its growth in the overlaps can lift tiles slightly and wick water where it should not go. On concrete tiles the sustained moisture accelerates surface erosion, which is why heavily mossed roofs shed so much grit into their gutters.

Can I pressure wash my own roof?

It is not recommended, on two grounds. High pressure damages tile surfaces, dislodges pointing and forces water under the overlaps — roofs are cleaned with low-pressure methods and treatments that kill the growth instead. And working on a roof is genuinely dangerous without the right equipment and anchor points; wet, mossy tiles are exactly the surface people slip on.

How often do Melbourne roofs need cleaning?

There is no fixed interval — it depends on tree cover, shade and the roof material. The practical approach is to check the signs once a year: streaking, moss in the overlaps, lichen spread and what is coming down the downpipes. A roof under open sky may go many years between cleans; a shaded roof under trees will not.