Water Running Down The Wall Behind The Gutter

What's happening?

Water getting behind a gutter usually means the eaves detail is wrong rather than the gutter being faulty. On a correctly built roof, the underlay is dressed over an eaves carrier tray so anything running down the underlay drops into the gutter. Where the underlay was cut short or has shrunk back, that water discharges behind the gutter instead, straight onto the fascia and down the wall. The other version is geometry: if the gutter sits too low or too far out relative to the tile edge, fast run-off in heavy rain clears the back or front of it. The signature is distinctive: a permanently damp stripe on the wall, often with green algae or moss, in a place where the gutter itself looks perfectly healthy.

What usually causes it?

• Roof underlay dressed short at the eaves with no carrier tray, or shrunk back over time so its lower edge pulls clear of the gutter line, leaving it to drain behind the gutter
• Gutter set too low, so water running off the tiles overshoots the back edge in heavy rain
• Gutter fitted too tight to the fascia with no clearance, so water wicks down between them
• Gutter dropped at the back where brackets have loosened, tipping water towards the wall
• Missing or displaced eaves course tiles letting water onto the fascia rather than into the gutter
• Capillary action along a mortar or sealant bridge between the gutter back and the fascia or wall
• Failed or absent eaves tray behind a replacement gutter fitted without reviewing the detail

Is it dangerous?

Not to people, but this is one of the more damaging eaves faults because it is continuous and hidden. Every rainfall wets the same strip of wall and the same length of fascia, which is exactly the condition wet rot needs and exactly how a wall becomes saturated enough for penetrating damp inside. The water is also going into the roof edge, wetting rafter feet and the wall plate: the timber the roof bears on. Because the gutter looks fine, this fault often runs for years and is diagnosed only when someone investigates damp on the inside of that wall.

Can I fix it myself?

Observe only from a safe ground-level position, and photograph the visible water path or staining. Do not climb to the eaves, enter an unsafe loft, touch loose guttering or insert sealant to redirect the water. A specialist needs to inspect the gutter and roof edge before the cause and repair can be established.

When should you call a fascia, soffit and guttering installer?

Call within weeks. There is no dramatic failure coming, but the damage is continuous and it is wetting structural timber, so it does not pay to leave. Bring it forward if damp has appeared inside on that wall, if the fascia is soft, or if you can see the underlay edge short of the gutter in the loft. Say clearly that the gutter is clear and not overflowing, so the visit is about the eaves detail rather than another gutter clean.

What will the fascia, soffit and guttering installer actually do?

• Watch or water-test the eaves to confirm where the water actually leaves the roof
• Take the gutter off and inspect the underlay edge, fascia and rafter feet behind it
• Fit eaves carrier trays under the underlay, extending or renewing short-dressed underlay, so it discharges over the tray into the gutter rather than the water being redirected at the gutter
• Re-set the gutter height, projection and back clearance so tile run-off lands in it and nothing bridges to the fascia
• Replace decayed fascia and splice rafter feet where the long-term wetting has caused rot
• Remove any mortar or sealant bridge between the gutter, fascia and wall, and re-bed or replace displaced eaves course tiles

Send ground-level evidence and an access brief

Photograph the affected wall and gutter from the ground when conditions are safe. Say whether the gutter was recently replaced, where water appears during rainfall, whether it overflows and whether indoor damp has appeared nearby. An observed water path is useful evidence, not proof of one hidden cause.

Give building height, rear access, parking and any conservatory or extension beneath the affected area. Ask whether the quote covers gutter adjustment, an eaves or roof detail, damaged timber, access equipment and making good. Agree investigation before assuming a gutter clean or another replacement will fix it.

Compare repair scope and exclusions

Describe your gutter repair

Who fixes this

• Gutter repair

Questions people ask

Sources & References

1. Approved Document C: Resistance To Moisture
2. BS 5534: Slating And Tiling Code Of Practice
3. PCA: Maintaining Your Outside Walls And Renders
4. NFRC: Technical Guidance