Gutters and downpipes have one job: to carry rainwater away from the roof and walls. When they fail, the water goes somewhere else. On the outside it soaks into brickwork, rots timber and stains render. On roofs with hidden gutters, it can come straight inside.
This guide explains the common faults, which gutters cause the worst damage and what to check.
How gutter faults cause damp
A blocked gutter overflows. Water then runs down the face of the wall instead of into the downpipe. Over time that can lead to damp patches inside, damaged pointing, stained render and rotten fascias and window frames. A leaking joint or a cracked downpipe does the same thing on a smaller scale, often in the same spot every time it rains. Because the damage builds slowly, it’s easy to blame something else, such as rising damp or condensation.
Ground-level problems matter too. If a downpipe discharges against the wall or onto a blocked gully, water can soak into the base of the wall.
Common faults
- Blockages from leaves, moss, silt and debris from the roof. Trees such as London planes and oaks shed a lot of leaves.
- Sagging runs where brackets have failed, so water collects in dips and spills over.
- Leaking joints in plastic or cast iron gutters.
- Cracked or rusted cast iron on older houses.
- Blocked hoppers and downpipes, which back water up along the whole gutter.
- Rotten fascias and soffits behind the gutter.
- Undersized gutters that can’t cope with heavy downpours, especially where an extension or new roof sends more water into an old run.
Overflows on parapet and box gutters are worth checking too. They’re there to let water escape safely if the main outlet blocks. If an overflow is missing or blocked, water has nowhere to go but inside.
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The gutters that do the most damage
Eaves gutters on the outside of a house overflow down the wall. Hidden gutters overflow inside. These include:
- Valley gutters in the middle of butterfly roofs and between roof slopes
- Parapet gutters behind front walls on terraces and older buildings
- Box gutters on larger and commercial buildings, often between roofs.
When these block, water rises above the lining and runs into the roof structure and ceilings. They’re also harder to see, so faults go unnoticed. Our guide to butterfly roofs and valley gutters covers this in more detail.
What you can check yourself
Safely, from the ground or from windows:
- watch the gutters in heavy rain for water spilling over
- look for plants growing from gutters or hoppers
- check for dark streaks or green staining on walls under gutters
- look for dripping joints and loose brackets
- check where each downpipe discharges at ground level.
Don’t lean ladders against plastic gutters or climb to reach them. Our winter roof checklist has more simple checks.
What a gutter survey covers
A gutter survey looks at eaves gutters, valley, parapet and box gutters, outlets, hoppers, downpipes, overflows, fascias and soffits. It covers above-ground rainwater only. It isn’t a CCTV drain survey. Where damp inside is the main worry, a roof leak investigation can look at the gutters and the rest of the roof together. Surveys start from £150, including VAT.
Quick answers
How often should gutters be cleared?
It depends on nearby trees and the roof. Many homes need it at least once a year, after autumn leaf fall. Homes near large trees may need it more often.
Can a gutter cause damp inside?
Yes. Overflowing gutters soak the wall, and hidden valley and parapet gutters can overflow straight into the roof and ceilings.
Do you survey underground drains?
No. Our gutter survey covers above-ground rainwater goods only. Underground drains need a CCTV drain survey from a drainage specialist.
Related services
More advice
- Butterfly Roofs and Valley Gutters Explained
- Winter Roof Checklist for Homeowners
- Moss on Roofs: Harmless or a Problem?
- Why Roof Leaks Are So Hard to Find
- All advice
This guide is general information about roofs and roof surveys. It isn’t legal, insurance or structural engineering advice; for those, speak to a suitably qualified professional.