Moss & algae removed at the root — without pressure damaging your tiles
Pressure washing looks like the obvious fix for a mossy roof, but it strips granules, forces water under tiles, and does nothing about the growth still rooted underneath. Roof cleaning here is done by softwashing instead — low pressure, proper dwell time, and a preventative treatment that keeps the roof clear for years, not months.
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How Roof Softwashing Actually Works
Moss and algae don't just sit on top of roof tiles — they take hold in the microscopic texture of the surface and spread from there, holding moisture against the roof long after rain has stopped. Left long enough, that moisture works its way under tiles and slates and starts causing damage that has nothing to do with how the roof looks.
Why Pressure Isn't Used On Roofs
A pressure washer looks like the obvious tool for the job, but on a roof it does more harm than good. High-pressure water strips the granules off asphalt shingles, forces water up under overlapping tiles, and can crack older or more brittle roofing material outright. It also just blasts the moss off the surface without doing anything about what's still rooted in the texture underneath — so it grows back within a season or two.
The correct approach is softwashing: a low-pressure application of a cleaning solution that kills moss, algae and lichen at the root, rather than physically scouring it off. The growth dies, loosens naturally, and is rinsed away at low pressure — no risk to the tiles, and a result that actually lasts.
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Brush Off Loose Material
Before any chemical goes down, loose moss, leaf litter and debris get brushed off by hand. This means the cleaning solution goes to work on what's actually rooted to the tile, instead of being wasted soaking into loose material that was coming off anyway.
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Protecting What's Around The Roof
Gutters, downpipes, plants, and anything below the roofline get covered or accounted for before any solution is applied.
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Applying The Softwash Solution
A professional-strength sodium hypochlorite solution, boosted with a surfactant to help it cling to tiles and penetrate moss growth, is applied at low pressure across the affected areas. The surfactant matters most on heavier moss, since it stops the solution simply running off before it can take effect.
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Dwell Time
The solution is left to work for a short period — roughly 15 to 60 minutes depending on how established the growth is — before rinsing. This is what actually kills moss and algae at the root, rather than just knocking it off the surface.
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Low-Pressure Rinse
Once the dwell time's done, a gentle rinse clears away the now-dead moss and algae and any residue. Still low pressure — enough to clean, not enough to damage tiles or force water underneath them.
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Preventative Biocide Treatment
Once the roof is clean, a DDAC-based biocide is applied as a preventative treatment. This doesn't clean anything itself — it's there to slow new moss and algae spores from establishing, which is a big part of why the results last as long as they do.
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Gutter Check
Moss and debris that's ended up in the gutters during the process gets cleared, so rainwater can flow off the roof properly afterward.
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Final Inspection
A last check confirms the roof is clean, nothing's been missed, and there's no damage from the process.
Because the softwash solution kills moss and algae at the root, and the preventative biocide helps slow new growth taking hold, regrowth is typically much slower than after a pressure wash — often a couple of years rather than a single season. How long it stays clear depends on the roof's aspect (shaded, north-facing roofs regrow faster), local climate, and tree cover.
Pricing differs for single-storey (bungalow) roofs versus multi-storey properties, mainly because of the access, safety equipment, and time involved in working at height — not because the cleaning process itself changes. Dormer windows (the peaked sections poking up from the roofline) are priced as a small surcharge each, since they add extra edges, angles and time to the job regardless of the roof's overall size.
Not sure whether this process actually holds up?
Fair enough — don't just take our word for it. Copy the prompt below into ChatGPT, Claude, or whatever AI tool you use, and ask it to independently check the process described on this page.
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