How to get rid of moss and lichen on a roof

Updated 2026-10-06

The reliable way to get rid of moss and lichen on a roof is to kill it with a roof treatment sprayed at low pressure, then let the weather carry it off. Scraping and blasting look quicker but cause more trouble. This guide covers what works in New Zealand conditions, what to avoid and what you can safely do from the ground. For the done-for-you version, see our roof moss and lichen treatment service.

What kills moss on a roof best?

A biocide made for roofs, usually a quaternary ammonium compound such as benzalkonium chloride, sprayed onto a dry roof and left there. It kills moss, lichen, algae and the spores sitting on the surface, so regrowth is slower than after scrubbing. Moss normally browns within days to a few weeks. After that, the dead growth needs rain and time to come away.

These are the same spray-and-leave moss and mould treatments you find at the hardware store, and roof treatment contractors use the same chemistry. The difference with a professional job is mostly in the application: even coverage of the whole roof, the right strength, and getting it done without anyone walking the roof or letting run-off reach the drains.

You’ll also see powders and zinc or copper strips sold as moss preventers. We haven’t found independent New Zealand evidence on how well they work on roofs, so we don’t recommend them. One caution is documented: a roofing maker warns that water running off copper onto zinc-aluminium coated steel speeds up corrosion of the steel, so copper has no place above a steel roof.

What’s the fastest way to remove moss from a roof?

The fastest-looking ways are scraping and water blasting, and both tend to cause more problems than they solve. They take visible moss off in an afternoon but can strip coatings and crack tiles, they leave spores behind, and on a roof containing asbestos high-pressure spraying is prohibited outright. A treatment is slower to look good, but it kills the growth without damaging the roof.

The asbestos point is not a technicality. WorkSafe warns that buildings from before the 2000s may contain asbestos materials and that decramastic tiles laid before the phase-out may contain it. In the case behind that alert, a 1970s decramastic roof was water blasted and asbestos debris ended up inside the house. Older roofs get a low-pressure method only, and it pays to check first.

If you need the roof to look clean soon, for a sale or ahead of painting, the honest quick route is a treatment followed some weeks later by a low-pressure soft wash that rinses off the dead growth. Concrete tile makers advise against pressure washers too, so skip the blaster even on newer tiled roofs.

How do you get rid of lichen on a roof?

Treat it with the same kind of roof biocide and be patient. Lichen is stuck tight to the surface and dies well before it lets go. You’ll usually see it change colour within days to a few weeks, but roofing makers say lichen can take many rainfalls and up to about six months to clear. A second application one to two months after the first helps with heavy growth.

Scraping is a poor alternative. The metal roofing industry’s lichen guidance says physical removal rarely gets all of it and lichen tends to grow back quickly, so it recommends chemical treatment. It also warns that lichen can work into a painted surface and cause permanent damage, which makes painted iron roofs worth treating early.

Lichen’s toughness is the reason it suits a roof. Te Ara explains that a lichen is a fungus living with an alga or cyanobacterium, and that lichens shut down in dry spells and start up again when the rain comes. A lichen patch can sit out a dry summer and carry on with the first autumn showers, which is why one treatment rarely clears it overnight.

Do homemade lichen killers work?

Some will kill lichen on a small patch, but none is a safer or better choice for a whole roof. Household bleach has official backing for some roofs and real drawbacks on others. We haven’t found reliable New Zealand evidence that vinegar or baking soda clears roof lichen. And anything you pour on a roof ends up in the gutters and downpipes.

• Bleach (sodium hypochlorite). BRANZ’s Level guidance gives a mix of 1 part household bleach to 4 parts water for moss and mould on roofs that feed water tanks, with the tank disconnected first and a thorough rinse afterwards. The steel industry also uses a dilute hypochlorite wash for lichen on painted steel. But stone-chip metal tile makers say hypochlorite should never go on their tiles because it can affect the coating.
• Vinegar and baking soda. Both get recommended online. We couldn’t find roof testing to back them up, so treat them as unproven and test on a small, reachable patch before relying on them.

Whatever you use, Auckland Council’s guidance applies just the same as for a bought product: treat it as a harmful chemical, don’t apply it when rain is forecast and keep the run-off out of the stormwater. Product labels also suggest wetting nearby plants with water before and after spraying.

Can you treat a roof yourself safely?

Yes, if you stay on the ground or on a ladder at the gutter line, and never walk on the roof. A hose-end sprayer used from the ground covers the lower part of many single-storey roofs. Anything you can’t reach that way is a job for someone with planned access and fall protection. WorkSafe’s working at height guidance is clear that there is no minimum height below which a fall can be ignored.

• Pick a dry day with no rain forecast. One treatment maker asks for at least 4–5 dry hours after spraying.
• Disconnect any downpipe that feeds a rainwater tank and leave it off until the roof has been rinsed with clean water or had a few heavy rains.
• Divert downpipes that drain to the stormwater onto lawn or garden well away from drains.
• Wet nearby plants before and after, and keep spray off decks and paving that drain to a sump.
• Wear gloves and eye protection. Some roof treatments are classed as corrosive to skin and eyes on their safety data sheets.
• Set the ladder on firm, level ground with someone holding it, and never step off it onto the roof.
• On an older or decramastic roof, spray and leave only: no scraping and no blasting.

If the roof is two storeys, steep or mostly out of reach from the ground, that is the point where paying someone with the right access gear makes sense.

How do you stop moss and lichen coming back?

You can’t stop spores landing, but you can make the roof a worse place for them. Cut back branches that shade the roof or drop leaves on it, keep gutters and valleys clear so water drains away, and re-treat before growth gets heavy. A roof that dries quickly after rain grows far less, and a treatment every few years usually keeps it in check.

Spores can sit on a roof for up to two years before anything shows, according to one roofing maker, which is why a roof can go from clean to green quickly. Treating before the growth is obvious kills them early. Once the dead growth has washed down, book a gutter clean so it doesn’t block the downpipes.

Shaded south faces and the strip under big trees will always be the first to come back, so keep an eye on those each autumn.