How often should you clean your roof?

How often does a roof need cleaning?

For most homes, every two to four years. A roof that has been cleaned and treated with a biocide usually stays clear for that long before moss starts to come back. Where your roof falls in that range depends mostly on how much sun and shade it gets.

A guide, not a rule: the conditions on your roof matter more than the calendar.

The biocide is what stretches the time between cleans. It kills the spores and roots left on the tiles, so growth is slower to come back. That’s why every Washmates roof clean is a soft wash followed by a biocide.

What makes moss come back sooner?

Moss, lichen and algae all need damp to grow, so anything that keeps the roof wet for longer brings the next clean forward:

• Trees nearby. Overhanging branches shade the roof and drop leaves onto it, where moss can take root.
• A north-facing slope. It gets little direct sun, so it stays damp for longer after rain.
• A low pitch. Low-pitched roofs are more prone to moss than steep ones.
• Rough-faced concrete tiles. Their surface catches dirt from the rain, and moss roots in it. Smoother slate and many clay tiles tend to grow less moss.
• A damp spot. Roofs that stay wet long after rain, or that take the brunt of driving rain, are more prone to moss and algae.
• Blocked or leaking gutters. Water that can’t drain away keeps the bottom edge of the roof wet.

A roof in an open, sunny spot with a steep pitch and no trees close by can go much longer between cleans than one tucked under trees on the shady side of a street.

How do you know your roof needs cleaning?

You can usually tell from the ground. It’s time to book a clean when:

• Moss is spreading. Green patches are joining up across the roof.
• Moss is building up along the edges. Clumps sit along the bottom edges of the tiles, in the gaps where they overlap, or around the ridge.
• The gutters keep filling with moss. Clumps washed off the roof are landing in the gutters and downpipes.
• Dark streaks or crusty patches are spreading. Black streaks are usually algae and crusty patches usually lichen; see what the black streaks on a roof are.

Some signs point to a roofer rather than a cleaner. If you see cracked, slipped or missing tiles, bits of tile surface in the gutters, or damp in the loft, get the roof checked first. Our guide to whether moss damages roof tiles explains what to look for.

What can you do between roof cleans?

You can’t stop moss altogether, but you can slow it down from the ground:

• Keep the gutters clear. Gutters typically need clearing once or twice a year, more often under trees. See what gutter cleaning costs.
• Cut back overhanging branches. Less shade and fewer leaves on the roof mean it dries out faster.
• Look at the roof each autumn. Moss grows most in the cool, damp months, so autumn is when you see how it’s doing.
• Think about copper or zinc strips. A roofer can fit them along the ridge to slow regrowth.

Don’t climb onto the roof to scrape or jet wash moss between cleans. Walking on tiles can crack them, a pressure washer can strip their surface and force water underneath, and falls from height are the most common cause of fatal accidents at work in Great Britain. See whether pressure washing damages a roof.

Is it cheaper to clean a roof more often?

Not usually. A clean with a biocide lasts two to four years, so there’s little to gain from booking one before the moss starts to build up again. Leaving it too long has its own cost, though: thick moss holds more water against the tiles and fills the gutters, and light moss is easier to clear than a thick build-up.

A Washmates roof clean starts from £800, and most UK homes pay £600 to £1,300. Every roof clean includes the gutters, fascias, soffits and any solar panels on the roof, so it’s all done in one visit every few years. You can see typical roof cleaning prices by type of house in our cost guide, and whether roof cleaning is worth it for your roof.

When is the best time to book the next clean?

Spring and early autumn usually give the best conditions, because the weather is mild and fairly dry and the biocide needs a dry spell after it goes on. Washmates cleans roofs in dry or mild weather and in light rain, never in heavy rain, frost, ice or high winds. See the best time of year to clean a roof.

If the moss is already thick, don’t wait for the ideal season. Tell us about your roof and we’ll send you a fixed price, usually without a site visit.