Why is water running down the wall behind my gutter?
Water getting behind the gutter is soaking the fascia and the wall rather than draining away, and it is nearly always a detail at the roof edge rather than a gutter fault.
- Difficulty
- intermediate
- Time
- 30 min
- Read
- 3 min
- Safety
- warning
Short answer
Water should leave the roof covering and land inside the gutter. When it runs back under the tile edge instead, it passes behind the gutter and down the fascia. The usual causes are a missing or wrongly-set eaves tray, felt that has perished or been cut short, or a gutter fitted too low or too far out.
This one matters more than most gutter faults because the water goes somewhere damaging. Instead of being carried away it soaks the fascia, the wall head and often the top of the cavity, and it does so every time it rains. Rotting fascia and a damp patch on an upstairs ceiling or wall are the usual first symptoms.
Safety
Step by step
- Confirm the symptom from the ground in rain.Look at the gap between the wall and the back of the gutter. Water visibly running down the fascia, or staining and green growth on the wall directly under the gutter line, both point to this.
- Look at what the roof covering overhangs.The bottom edge of the tiles or slates should discharge over the gutter, not short of it. A roof edge that stops behind the back of the gutter drops water into exactly the wrong place.
- Check for an eaves tray or felt support.A tray at the eaves carries water off the underlay and over the gutter's back edge. If the underlay stops short, has perished, or has sagged behind the gutter, water finds its way behind instead.
- Consider whether the gutter has been fitted too low.Gutters replaced without care are often set lower or further out than the original, which puts the back edge below the line the water leaves the roof at.
- Rule out simple overflow first.A gutter running full spills in both directions, including backwards. Clear and check the flow before concluding that the roof edge is at fault.
- Look at the fascia for the consequences.Soft, dark or blistered timber, or a wet strip behind the gutter, tells you how long this has been going on and how much of the repair is fascia rather than roof edge.
- Get the roof edge looked at rather than sealing the gap.The common instinct is to run sealant along the back of the gutter. It does not address the water path, traps moisture against the fascia and makes the eventual repair worse.
- Check inside for consequences before assuming it is only external.Damp at the top of an upstairs wall, or staining on the ceiling near the external wall, often traces to exactly this.
Common mistakes
- Sealing the gap between gutter and wall. — It does nothing about water arriving behind the gutter and holds it against the timber, accelerating the rot it was meant to prevent.
- Assuming it is a gutter fault and replacing the gutter. — A new gutter in the same position, with the same roof edge detail above it, does the same thing.
Questions people ask
Is this an urgent repair?
More urgent than most gutter faults, because the water is going into the structure rather than onto the ground. It is worth getting looked at before a wet winter rather than after.
Can I fit an eaves tray myself?
It involves lifting the bottom course of tiles and working at the roof edge, at height. For most people this is a job to have done rather than to attempt.