Is my damp wall caused by the gutter?
Rainwater faults are one of the most common causes of a damp patch, and they are distinguishable from other causes by where the damp is and when it appears.
- Difficulty
- beginner
- Time
- 30 min
- Read
- 2 min
Short answer
Damp from guttering follows the rain: it appears or worsens during and after wet weather and dries slowly in between. It is usually a defined patch rather than a general dampness, sits high on the wall for a gutter fault and low for a downpipe one, and lines up with something outside.
Before spending money on damp treatment, it is worth ruling out the cheapest possible cause. A blocked gutter, an overflowing joint or a splashing downpipe delivers many litres of water onto one small area of wall every time it rains, and no internal treatment will out-compete that.
Step by step
- Note when the damp appears and when it fades.Damp that tracks the weather — worse during and just after rain, improving in a dry spell — points strongly at water getting in from outside. Damp that is constant regardless of weather points elsewhere.
- Note where it is on the wall.High up near the ceiling suggests the gutter, the roof edge or the wall head. A vertical band suggests a downpipe. Low down along the skirting suggests ground level, splashing or something unrelated to rainwater.
- Go outside and line the patch up with what is above and beside it.Stand outside and find the same place on the elevation. A gutter joint, a downpipe, a valley discharge, a blocked outlet or a wet band of wall directly above the damp is the answer more often than not.
- Look at the wall in heavy rain.This is the highest-value ten minutes in the whole diagnosis. Faults that are invisible in dry weather are obvious while it is raining.
- Check for the other rainwater causes covered separately.Overflowing, water running behind the gutter, overshooting at a valley and splashing at the base of a downpipe each produce a characteristic pattern.
- Check ground levels and paving too.Rainwater faults often combine with a high ground level or paving falling towards the house. Either alone may be tolerable; together they are not.
- Fix the water before treating the wall.Replastering, sealing or applying a damp coating to a wall that is still being soaked from outside will fail, sometimes quickly. The order matters.
- Allow a long time for the wall to dry afterwards.A saturated masonry wall takes months to dry, not days, and it dries from the surface inwards. A patch that is still visible weeks after the repair does not mean the repair failed.
Questions people ask
How do I tell this from rising damp?
Rising damp is low on the wall, fairly constant, and has an upper limit. Rainwater damp tracks the weather and usually lines up with a specific external feature. GuideHQ has separate guides on diagnosing damp types.
Could it be condensation instead?
Condensation is worse in cold weather rather than wet weather, appears on cold surfaces and in corners, and is often accompanied by black mould. Rainwater damp is a defined patch that follows the rain.