Removing moss and green algae from your roof: DIY or roofer?

Short answer: moss and green algae on a low roof that you can safely reach from the ground or a sturdy ladder, such as a shed, carport or single-storey extension, can be tackled yourself with a soft brush, an algae cleaner and a pressure sprayer. Leave the main roof of your house to a roofer. A green roof is as slippery as ice and a fall from that height can be fatal. Never use a pressure washer on roof tiles.

👷 Calling in a professional is never unnecessary, and on a pitched roof at first-floor level or higher it is the only safe choice. A roofer works with fall protection, spots loose or cracked tiles straight away and replaces them before they start to leak.

Why does moss grow on your roof?

Moss and algae love moisture and shade. On the north side of the roof, under overhanging trees and on porous, older tiles, water stays longer. Leaves and dirt in the gutter keep the lower rows wet, so that is where growth settles first. A little green is mainly a cosmetic issue. Thick layers of moss are a risk, though: they hold water, can damage the tiles when it freezes and wash into the gutter when it rains, blocking it. Read in our blog on cleaning gutters: DIY or professional how to get the gutter clear again.

What can you do yourself?

Doing it yourself is sensible when all of these conditions are met:

• The roof is low: a shed, garden house, carport or single-storey extension.
• You reach the work from the ground or from a sturdy ladder, without stepping onto the roof itself.
• The tiles are secure and intact. If you see shifted or broken tiles, first read our blog on checking your roof after a storm.
• The weather is dry and no rain is expected for the next two days.

If you have doubts about any of these points, choose the roofer.

⚠️ Roofs built before 1994 may have corrugated sheets or slates containing asbestos. If you are unsure about the roofing material, do not brush or scrape it, and have it tested by a certified company first.

How to tackle a low roof

1. Clean the gutter and remove loose leaves so the water can drain away later.
2. Gently brush away thick patches of moss with a hand scrubbing brush or a 220 mm scrub broom, from top to bottom, following the overlap of the tiles. Do not use a wire brush: it scrapes away the top layer of the tile, after which the green comes back faster.
3. Apply the cleaner. Dilute the roof and facade cleaner for moss and lichen in a 12-litre bucket exactly as the instructions say and fill a 2-litre pressure sprayer for a small roof or a 15-litre pressure sprayer for a larger area. A telescopic lance for pressure sprayers gives you more reach without stretching. A cordless sprayer saves your arm on a large surface.
4. Let the product work. The growth turns dark over a few days and dies off. It must stay dry during that time.
5. Rinse gently with a 20-metre garden hose and a adjustable spray gun on a soft spray, or let the rain do the job if the instructions allow it.
6. Check the gutter again for loosened moss and debris.

💡 Protect plants, ponds and the water butt under the roof while spraying, and temporarily disconnect the downpipe if needed. Never work in wind, so the mist does not blow onto your skin or towards the neighbours.

Why not a pressure washer?

A pressure washer removes moss quickly, but also the protective top layer of the roof tile. The tile becomes rougher and absorbs more water, so the green actually returns faster. In addition, the hard jet can drive water under the tiles and blow tiles loose. Patio tiles are a different story; read our blog on cleaning patio tiles for that.

When do you call the roofer?

• It concerns the main roof or a pitched roof that you would have to stand or hang on.
• There are loose, cracked or shifted tiles, or there is a leak in the attic.
• The growth sits deep in the tiles and does not come loose after treatment.
• You want a protective treatment applied after cleaning.

A roofer often combines cleaning with a check of ridge tiles, lead flashing and gutters. That is a good moment to get your house ready for winter as well; read our blog on getting your home ready for winter.

Working safely

For a DIY job, do not stand on the roof. Work from the ground or place a three-section ladder with 3 x 9 rungs on a level, firm surface, let it extend at least one metre above the roof edge and have someone hold the ladder. Anyone working at height with a safety harness must know how and where to anchor it safely: that is a professional's job. Wear safety goggles against splashes of cleaner, work gloves with nitrile coating against the product and dirty water, and safety footwear with a good tread, such as a low S3S safety shoe. A safety helmet protects you if a tile or branch comes down.

How often should my roof be cleaned?

That depends on its position. A roof in the shade under trees needs attention sooner than a roof in full sun. A few tufts of green are no reason to act; thick moss and blocked gutters are.

Can I use bleach or vinegar?

No. Aggressive products attack tiles, zinc work and plants. Use a product intended for roof tiles and follow the instructions.

Will the moss come back after cleaning?

Eventually, yes, especially on the shady side. Prune overhanging branches, keep the gutter clean and check the roof from the ground every autumn.

With a soft brush, a good cleaner and patience you can keep a low roof clean yourself. If you have to go onto the roof, the roofer is the safe choice.

Where can you find everything for this job?

At Saniso, the online store for DIYers and professionals, you will find tools, materials and personal protective equipment for your job.

• Browse our construction tools and our workwear and safety.
• Create a customer account and order easily.
• Working on a bigger project or want to hand over the job? Request a project quote.
• Book a showroom visit, at least 24 hours in advance.
• Not sure which material suits your job? Get in touch with us.

In doubt about the approach? Feel free to call in a professional.

Saniso – Build your home with Saniso.