Why is the wall wet when the gutter is not overflowing?

Because the water never reaches the gutter. Where the roof underlay stops short of the gutter, everything running down it discharges behind, onto the fascia and the wall. The gutter can be spotless and still be irrelevant to that water path.

What is an eaves carrier tray?

A rigid tray fitted at the bottom of the roof slope that supports the underlay and carries whatever runs down it out over the front of the fascia, into the gutter. It is the component most often missing on older roofs and on gutters replaced without reviewing the detail.

Can this be fixed without touching the roof?

Sometimes. If the cause is purely gutter height or back clearance, re-setting the gutter is enough. If the underlay is short, the tiles at the eaves course have to come off to fit a tray, so it becomes a small roofing job. Which one it is can only be established by taking the gutter off and looking.

Is the green algae stripe on the wall a problem?

The algae is only the marker — it grows because that strip of wall is permanently damp. The problem is the moisture in the masonry and the timber behind it. Cleaning the wall without fixing the water path just gives you a clean wall that goes green again.

Caution

Updated 30 August 2026

Water Running Down The Wall Behind The Gutter

The gutter is clear and not overflowing, but there is a wet stripe or green algae growth on the wall directly beneath the eaves.

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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?

Watch it rain, which is the only reliable way to see this. Stand back and look at the eaves during a downpour: water visibly appearing behind or beneath the gutter line while the gutter itself flows normally is the diagnosis. Between showers, look for the tell-tale permanent damp stripe or algae on the wall directly under the eaves, and check whether the fascia behind the gutter is stained or soft. In the loft, look at the lower edge of the underlay — if you can see it stopping short of the gutter, that is the fault. Do not try to stuff sealant or mortar between the gutter and the fascia; a bridge there makes capillary transfer worse.

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

Frequently asked questions

We’re happy to answer all your questions.

Sources & References

Rotten Fascia BoardCaution Gutter Overflowing In Heavy RainCaution Penetrating Damp On An Internal WallCaution

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