Roof soft washing is a chemical treatment rather than a blast of water. A solution goes on the tiles or the sheeting, it kills the moss, lichen and black algae growing there, and the roof is rinsed at low pressure. On a Melbourne roof that is the only method worth using, because the alternative, a high pressure lance on a tiled roof, does more damage in an afternoon than ten years of moss.
Roofs are the part of the house nobody looks at. You see the fascia and the gutter line from the footpath and that is about it. Then a neighbour puts a drone up, or you get the real estate photos back, and there is a green and black stripe running down the shaded half of the roof.
What grows up there
Three things, mostly, and they turn up in that order.
Black algae comes first. It is the dark staining that runs in streaks down from the ridge, worst below anything that stays damp. People assume it is dirt. It is a living growth feeding on the mineral content of the tile, and hosing it does nothing because the surface holds it.
Moss follows on the shaded side. In the bayside and southern suburbs it is the south and south east faces, under gums and around anything overhung by a neighbour’s tree. Moss needs shade and moisture, and a tiled roof under a canopy gives it both for most of the year.
Lichen is the stubborn one: flat grey and orange discs stuck hard to the tile. Lichen grips into the surface rather than sitting on it, which is why scraping takes the tile finish with it and why it needs a treatment and time rather than force.
Why moss on a roof matters
Moss holds water. A dry tile sheds a shower in minutes; a mossy tile stays wet for a day afterwards, and the tile under that mat of moss goes through wet and dry cycles constantly instead of drying out between rain. Concrete tiles are porous once their surface coating has worn, and constant damp is what wears it.
Moss also grows into the laps. It builds up between the overlap of one tile and the next, and as it thickens it lifts the tile slightly off its neighbour. That gap is where wind driven rain gets in during a spring storm. The other half of the problem is what happens when moss lets go, because it does eventually, usually all at once in heavy rain. It ends up in the gutters, packs into the downpipe outlets, and then the gutters overflow in the middle of the next storm. Plenty of blocked gutter callouts start on the roof.
Why high pressure ruins a tiled roof
A tiled roof is not a sealed surface. It is hundreds of separate tiles overlapping each other, designed to shed water running downhill. Point a pressure jet at it and you are pushing water sideways and uphill, straight into the laps. Under the tiles is sarking if you are lucky, and the ceiling if you are not. The leak often does not show up on the day. It shows up as a stain on a bedroom ceiling three weeks later.
The second thing high pressure does is strip the tile itself. Concrete tiles have a coloured coating on the surface. A jet takes it off, along with a layer of the cement underneath, and you can see it in the wash water running down: grey slurry, not dirt. A stripped tile is rougher and more porous than it was, so it soaks up water and grows moss faster. The roof looks great for a season and then goes backwards.
Ridge capping is the third casualty. The mortar bedding and pointing along the ridges and hips is the oldest and most fragile thing on most roofs, and pressure blows it out.
Colorbond and metal roofs
Colorbond does not hold moss the way a concrete tile does, but it collects its own problems. Salt air along the bay leaves a film that dulls the colour. Gum leaf litter sits in the pans and in the valleys and stains where it rots. The paint finish chalks with age the same way house paint does, and once it chalks it holds dirt.
Metal gets soft washed too, at low pressure, worked with the run of the sheeting rather than across it. What you avoid on Colorbond is anything abrasive: no scrubbing pads, no aggressive brushing, nothing that scratches the coating, because the coating is the corrosion protection. Screws and washers get a look while we are up there, since a perished rubber washer is a slow leak that costs a lot more than a wash.
Nobody should be walking their own roof
A wet tiled roof is about as slippery as a surface gets, and a tile that has been holding moss for five years is often cracked underneath it. Standing on the wrong one puts a foot through the ceiling. Melbourne roofs are also steeper than they look from the ground.
Our crews are work at heights certified and the business is public liability insured, and both of those matter more on a roof than anywhere else on a property. If the roof is two storey, or steep, or wet, that is a job to book rather than a Saturday.
Do the gutters and the panels at the same time
A roof wash puts a lot of dead growth into the gutters. Clearing them afterwards is part of the job, and if they were due anyway, that is the visit to do it on. Our gutter cleaning crews clear by hand and flush the downpipes, so anything the roof shed goes out rather than settling in the corners.
Solar is the other one. Panels sit in the same shade and the same leaf fall as the roof around them, and dirty panels can cut output by up to 25 percent, so there is a real reason to keep them clear. They are never high pressure washed either. If you have panels, book solar panel cleaning on the same day and the whole roof gets sorted in one visit.
Send us a photo of the roof from the yard or the street and we will tell you whether it needs a wash or just the gutters done. Our roof soft washing sits under house washing, quotes are free, and you can reach us on 03 8682 8767 seven days a week.