7 Signs Your Roof Needs Cleaning (And What Happens If You Ignore Them)

Most people only think about their roof when something goes wrong. By then the damage is usually done and the bill is bigger than it needed to be. The good thing is that a roof gives you plenty of warning first, if you know what to look for.

Here are the 7 signs your roof needs cleaning, what each one means, and what happens if you leave it. You can check nearly all of them from the ground with your phone camera, no ladder needed.

The 7 signs at a glance

1. Green moss between the tiles
2. Dark streaks running down the roof
3. Crusty white, grey or yellow patches (lichen)
4. Blocked or overflowing gutters
5. Grit from the tiles in your gutters or on the drive
6. Damp patches in the loft or on upstairs ceilings
7. Loose, slipped or missing tiles

If you can see two or more of these, it’s worth getting someone to look. Don’t panic though. Most of it is easy to sort when it’s caught early.

1. Green moss between the tiles

The obvious one, and the most common round here because of the damp weather. You’ll see soft green clumps between the tiles, usually on the north-facing side, in shade or under trees. (We explain why in our guide to why British roofs get so much moss.)

Moss holds water against the tiles like a sponge. In winter that water freezes and expands, and over a few years it cracks tiles, lifts them and loosens ridge mortar. It also washes down into the gutters and blocks them.

2. Dark streaks running down the roof

Black or dark green streaks running down the slope are usually algae, most often a type called Gloeocapsa magma. On its own it’s mostly a looks problem, but it keeps the surface damp and tends to be the first stage before moss and lichen move in.

3. Crusty white, grey or yellow patches

That’s lichen. It looks like flat, round, crusty patches stuck hard to the tile, and unlike moss it grips the surface itself. It grows very slowly, so if you can see a lot of it, it’s been there for years. It often leaves marks even after it’s taken off.

Pressure washing doesn’t help here. It strips the tile surface and leaves it rougher, which gives growth an easier time coming back. We take lichen off by hand and then apply a biocide to deal with what’s left in the surface.

4. Blocked or overflowing gutters

Next time it really rains, go outside and watch. Water should disappear down the downpipes. If it’s pouring over the front edge, the gutter is blocked, and very often it’s moss washed off the roof that’s doing it.

Overflowing water runs down the walls, soaks the fascia boards behind the gutter and can end up as damp inside. Clearing a gutter is a small job. Fixing what a blocked one does over a few winters isn’t.

5. Grit from the tiles in your gutters or on the drive

Concrete tiles have a gritty surface. When it starts to wear, you’ll find little granules in the gutters, the downpipe shoes or on the drive after rain, a bit like fine gravel. It means the surface is breaking down and the tiles will soak up more water. Old pressure washing is a common cause. Cleaning by hand and treating the roof won’t reverse it, but it stops the moss making it worse.

6. Damp patches in the loft or on upstairs ceilings

On a dry day, take a torch into the loft and look at the underside of the roof and the timbers. Check upstairs ceilings for yellow or brown stains too. If you can see damp inside, water has usually been getting in for a while. This is the one not to leave, because wet timber and insulation get expensive quickly.

7. Loose, slipped or missing tiles

You can often spot these from the ground: a tile out of line, sitting at a different angle, or a gap where one used to be. After a storm, have a look in the garden for bits of tile. A slipped tile lets rain straight in, and the wind gets under the gap and lifts more next time. Get it put back sooner rather than later.

A quick check you can do from the ground

Grab your phone and walk round the house:

• Stand back 20 to 30 feet from each side and zoom in on the roof
• Look for green clumps, dark streaks and crusty patches
• Check the ridge tiles are all in line and level
• Look for plants growing out of the gutters
• Check the drive and patio for grit or bits of tile
• Look at the fascias under the gutter for stains
• Inside, check the loft and upstairs ceilings for damp

Take photos as you go. If you send them over on WhatsApp, they help us understand what’s going on before we come out. We’ll still come and look in person before we give you a price, because photos can hide things.

When to call someone straight away

• Damp in the loft or stains on the ceiling
• Several slipped or missing tiles
• Moss covering a big part of the roof
• Grit from the tiles turning up after every bit of rain

For everything else, a look once a year, in spring or autumn, keeps you ahead of it. It’s also worth reading why regular roof cleaning extends the life of your roof.

Common questions

How often should I check my roof?

A quick look from the ground twice a year is plenty for most houses: once in spring after the winter, and once in autumn before it. And after any big storm.

Can I clean my roof myself?

On a low bungalow or a flat-roofed extension, a bit of moss can sometimes come off with a soft brush. On a two-storey house it really isn’t worth the risk of a fall. Get someone insured to do it.

What’s the difference between moss, algae and lichen?

Moss is soft green clumps that sit between the tiles. Algae is the dark streaks running down. Lichen is the flat, crusty patches stuck to the tile itself.

Will my home insurance cover moss damage?

Usually not. Most policies don’t cover damage that builds up slowly through wear and tear, and moss falls into that. It’s worth checking your own policy, but looking after the roof is the safer bet.

Will the moss come back after a clean?

In time, yes, especially in shade or under trees. The biocide treatment we use slows it down a lot. Our 12-month written guarantee covers our workmanship, but nobody can honestly promise moss won’t come back.

PrimeEdge Home Care Ltd is a family-run, fully insured roofing and exterior business based in Tadley, working across Hampshire and Berkshire, including Basingstoke, Reading, Newbury, Fleet and Andover. Every job comes with an invoice, a before-and-after photo report and a 12-month written guarantee on our work.