Most people never look at their own roof. You see it from the footpath at an angle, or in a real estate photo, and by then the moss has usually been there for years. Roof cleaning Melbourne homes need is rarely urgent in the way a blocked downpipe is urgent, but a roof that stays wet and dirty ages faster than one that gets cleaned every few years.
What builds up on a Melbourne roof
Four things, in roughly this order. Leaf litter and bark, which drop all year under gums and pile into the valleys. Black algae, which shows as streaks running down the pitch. Moss, which starts in the shade and in the laps between tiles. Then lichen, the grey and orange crusts that root into the surface of a tile and are the hardest of the lot to remove.
Aspect decides most of it. The south facing pitch of a roof gets less sun, dries slower and goes green first. A roof shaded by a neighbouring two storey house or an overhanging branch does the same thing. Bayside roofs pick up salt off the water, western suburbs roofs pick up more dust and traffic film, and both hold that grime until something washes it off.
None of this is only cosmetic. Moss and lichen hold water against the roof surface, and a roof tile that never fully dries stays porous and gets colder. It does not take much growth in the laps to lift tiles a fraction, and once they are lifted, wind and driven rain get underneath. On an older roof with no sarking, that water ends up in the roof space.
Tile roofs and Colorbond roofs are different roof cleaning jobs
A concrete roof tile has a glazed coating on it when it leaves the factory. That coating is what makes the tile shed water and resist moss. It wears with age, and once it has gone the tile drinks up water and grows moss faster every year. Clean a concrete roof tile with a high pressure wand and you take off whatever coating is left, which is why moss comes back sooner on a blasted roof than a treated one.
Terracotta is harder wearing on the surface but far more brittle underfoot, especially on a roof that has been up there since the 1930s. Old terracotta tiles crack under a boot in the wrong spot, and the crack often will not show until the next heavy rain.
A Colorbond roof grows less moss because there are no laps for it to sit in, but it still gets algae streaks, lichen spots and a dull layer of grime. The paint finish is the thing to protect on a Colorbond roof. It cleans up well at low pressure with the right treatment, and badly under a pressure wand held too close.
The other material question is what is on the roof already. Solar panels, whirlybirds, skylights and old flashings all change how a roof is cleaned, and anything cracked or loose is a repair for a roofer before it is a roof cleaning job. Roof cleaning makes a roof clean. It does not make it watertight.
The roof cleaning method: soft washing, not blasting
A roof soft wash uses the same low pressure method we use on the render and weatherboard of a house. The treatment kills the moss, lichen and algae at the root and is then left alone. The growth dies back and weathers off over the following weeks. Where the owner wants the bulk of it gone straight away, a low pressure rinse lifts the dead material once the soft wash has taken.
High pressure is not suitable for any roof surface. It forces water up under the tile laps and into the roof cavity, it strips the coating off concrete roof tiles and the finish off Colorbond, and it leaves a rougher surface that holds spores better than before, so the moss comes back quicker. Pressure has its place on a driveway. It does not belong on a roof.
Roof cleaning and roof restoration are not the same service, and it is worth knowing which of the two cleaning services you are being quoted for. Restoration means repointing the ridge capping, replacing broken roof tiles and spraying a new coating over the whole roof. Roof cleaning is the wash and the treatment. Plenty of roofs only ever need roof cleaning.
Nobody should be walking a wet tiled roof
Moss with water on it is as slippery as ice, and a tiled roof pitched at any decent angle gives you nothing to stop against. People still get up there with a ladder and a broom on a Sunday, and the ones who get hurt are usually not the careless ones.
Our crews are work at heights certified and we carry public liability insurance. Access is set up before anyone goes near the edge, and where a roof is too brittle or too steep to walk safely, it gets cleaned from ladders and from the edge instead of across the tiles. That is a judgement call made on the day, not one made from a photo.
What gets checked while we are up there
Roof cleaning is the one time in a few years that anyone is up close to the whole roof, so it is worth using. While the roof is being cleaned we note the condition of the ridge capping and whether the mortar is cracking, any roof tiles that are broken, slipped or repaired badly, the condition of the valleys, and how the flashings around chimneys and skylights are sitting.
You get told what we found. If it needs a roofer we say so rather than quoting you for a repair, because we clean roofs, we do not re-lay them.
The gutters are part of the same visit. Dead moss and loosened debris wash down the pitch into the gutters and downpipe outlets, so they are cleared and flushed at the end. If your gutters are the more pressing problem, book roof and gutter cleaning together and pay for the access once.
Questions we get asked about roof cleaning
How much does roof cleaning cost?
Roof size and pitch, what the roof is made of, how much growth is on it, how the access works, and whether the gutters are being done at the same time. A single storey Colorbond roof with light algae is a different job to a steep double storey roof of the same size in terracotta under gum trees. Quotes are free and we can often price a roof from photos, so upload a few taken from the ground on each side of the house and we will tell you what it needs.
Is professional roof cleaning worth it?
If the roof is green on one side, yes, because moss is holding water on a surface designed to shed it. If the roof is only a bit dusty, it is more of a presale job than a maintenance one. Ask what method the quote is based on before you compare roof cleaning services, because a cheap high pressure blast on a tile roof can cost you the coating.
What time of year is best to clean a roof?
Spring and early autumn suit a roof treatment best. The growth is active and the weather gives it time to dry between showers. Winter works too, it just weathers off more slowly. The one thing worth not doing is leaving it until the week the photographer arrives, because a treated roof keeps improving for weeks after the visit.
How often does a roof need cleaning?
Every few years for most homes, and more often for a shaded tile roof under established trees. A recent roof clean holds up longer if the gutters and valleys are kept clear in between, because wet debris sitting on the roof is what gets the moss started again.
If your roof has gone green, send us a couple of photos from the ground and we will tell you whether it needs a treatment now or whether it can wait. Quotes are free, we are out seven days a week, and where the rest of the exterior needs doing as well the same roof soft washing method covers the walls. Call 03 8682 8767 or upload your photos with an enquiry through the contact page.