Damp patch on the wall below your gutter? What it usually means

Where the damp is tells you where to look

Why gutters cause damp

A gutter that overflows drops water on exactly the same stretch of wall every time it rains. Cadw warns that if a leak is allowed to continue, "water damage can appear on the inner face of the wall". The damp company Timberwise lists failing gutters and downpipes as "one of the most common causes of penetrating damp", and notes that the patches "will grow in size during periods of heavy rainfall".

That link with the weather is the giveaway. Damp from a gutter tends to get worse after a wet spell.

Downpipes crack where you can't see

Downpipes usually fail on the side facing the wall. The Department for Communities in Northern Ireland, in its technical note on roof drainage, says faults are most common on the face against the building, so damp inside is often the first sign. Cadw makes the same point: "Holes at the back of downpipes can be difficult to spot, particularly with rectangular section pipes."

Frost makes it worse. If a downpipe is partly blocked and holding water, Cadw warns that "trapped water can freeze and split pipes".

The Northern Ireland note also says downpipes "must always be free of the wall surface and never embedded in the plaster". A pipe buried in render can leak into the wall without anyone seeing it.

What to check yourself, from the ground

• Go out in heavy rain and watch the gutter directly above the damp patch. Is water coming over the front, or running down behind it?
• Look along the wall beside the downpipe for rust stains, washed-out mortar, moss or algae. Cadw lists these as signs of a saturated wall.
• Using a torch, look at the joints in the downpipe and as much of the back as you can see. Take a photo with your phone held close to the wall if you can't see it yourself.
• Check where the downpipe ends. Is the drain or gully below it blocked with leaves, or is water pooling at the bottom of the wall?
• Check that soil, paving or a flower bed hasn't been built up against the wall. Cadw advises making sure soil hasn't risen above the internal floor level, the damp-proof course or any air bricks.

Don't climb a ladder to look. Cadw's advice is to consider the risks before any work at height, and a photo from the ground is usually enough for a roofer to tell what's wrong.

Gutter damp or something else?

Not every damp patch comes from a gutter. Damp low down on a wall can come from the ground or from bridging, which Timberwise warns can be misdiagnosed as rising damp. Damp in kitchens and bathrooms is often condensation, and damp on a ceiling can come from the roof itself or a plumbing leak.

The order matters. If the gutter and downpipe above the patch are clear, the joints are sound and the drain is taking the water, the gutter probably isn't the cause, and it's time for a surveyor rather than a roofer.

Fix the water first, then the wall

Treating or replastering a wall that's still being soaked from outside won't last. Cadw says water needs carrying away from the base of walls "as quickly as possible". Stop the water at the gutter or pipe, then let the wall dry out before deciding whether anything inside needs doing.

If you rent, tell your landlord in writing. Under section 11 of the Landlord and Tenant Act 1985, landlords must keep gutters and external pipes in repair.

How we check a gutter above a damp patch

We clear the gutter by hand, run water through the outlet and down the pipe, and look closely at the joints and the back of the downpipe where we can reach. Then we tell you whether the gutter is the likely cause, with photos. If a length is cracked, a joint is leaking or the gutter is set wrongly, we'll quote to fix it.

Written by Hawkes Roofing, roofers based in St Albans who clear gutters and downpipes by hand across Hertfordshire, Buckinghamshire and north-west London. Last reviewed 26 October 2026.