Ten Signs Your Roof Actually Needs Cleaning

The urgent signs

Some observations warrant attention within weeks rather than years. Water overflowing from a gutter during rain means the drainage path is blocked, and blocked drainage is the mechanism behind most damp problems that originate at roof level. Moss visibly bridging a valley — the sloping join between two roof planes — is the same problem in a worse location, because valleys carry a concentrated volume of water.

Clumps of moss regularly appearing on the ground or on the driveway after wind mean the growth is thick enough to shed. That material lands in gutters as well as on the lawn.

• Water overflowing gutters in ordinary rain
• Moss visibly filling a valley or behind a chimney
• Lumps of moss on the ground after wind or rain
• Damp patches on upstairs ceilings or chimney breasts
• Plant growth, not just moss, rooted in the gutter

The moderate signs

Thick, three-dimensional moss along the lower courses of tiles is worth acting on within a year. So is visible moss growth in the mortar of ridge and hip tiles, because moss retains moisture in mortar joints and accelerates their failure. Once ridge bedding starts breaking down, you are into repointing costs rather than cleaning costs.

Sagging or ponding in a gutter run, or a gutter that has visibly pulled away from the fascia, indicates weight from accumulated debris. Left long enough, brackets tear out and a section comes down.

The cosmetic signs

Flat black or green staining with no physical depth is algae and lichen, not moss. It does no structural harm at all. Cleaning it is a legitimate choice for appearance, particularly before selling a house, but nobody should be told it constitutes damage.

White or grey crusty patches are lichen, which bonds tightly to the surface. It is slow-growing, largely harmless, and much harder to remove than moss. On a sound roof it can reasonably be left.

Signs it is a repair job, not a cleaning job

If you can see a slipped, cracked or missing tile, a gap along a ridge line, or daylight visible through the roof from inside the loft, cleaning is not your first priority. Those need a repair, and any competent cleaner will tell you so rather than cleaning around the problem.

Likewise, sagging in the roof line itself, or a chimney stack that looks out of true, is structural. Get a roofer or surveyor before spending anything on appearance.

• Slipped, cracked or missing tiles
• Daylight visible in the loft
• Sagging roof line or bowing between rafters
• Cracked or leaning chimney stack
• Failed lead flashing around chimneys or abutments

How to check safely from the ground

You do not need to climb anything. A pair of binoculars and a walk around the property will show you almost everything on this list. Photograph each elevation with a phone at maximum zoom and compare the images year on year — changes stand out far more clearly than any single snapshot.

Check the loft too, on a bright day with the light off. Daylight, damp timbers and staining around chimney breasts tell you more than the outside of the roof does. If anything on the urgent list applies, arrange an inspection rather than guessing.

The bottom line

It is worth repeating the uncomfortable part of this checklist: several of these signs mean your roof does not need cleaning at all. Flat algae staining and slow-growing lichen on an otherwise sound covering are cosmetic. Cleaning them for appearance is a perfectly good reason, particularly before a sale, but it is a choice rather than a necessity, and anyone telling you otherwise is selling rather than advising.

Where the signs are genuinely on the urgent list — overflowing gutters, blocked valleys, moss shedding in clumps, damp appearing upstairs — act within weeks rather than seasons, because all four are drainage problems and drainage problems get worse with every wet month. Photograph what you can see, send the images over, and get an opinion before you get a quote. We will tell you honestly which list your roof belongs on.

Frequently asked questions