Why Is Water Running Behind My Gutter?

How water gets behind a gutter

A gutter is meant to catch everything that leaves the roof edge. Rain runs down the tiles, drips off the bottom row and falls into the channel. Any water that gets under the tiles is carried down the roofing felt, which should hang over the fascia and into the gutter. If something breaks that path, water finds the back of the board.

The common faults are these:

• The felt ends behind or above the fascia instead of draping into the gutter, so water that gets under the tiles runs down the back of the board.
• There is no eaves tray or support, so the felt sags and forms a dip where water pools and soaks the timber.
• The gutter is too high, tilted away from the roof or too far forward, so water dripping off the tiles lands behind it.
• The bottom row of tiles overhangs too little, so water runs down the underside of the tile and back onto the board.
• A blocked outlet fills the gutter, and water spills over the back edge as well as the front.

The first sign is often a dark stripe on the face of the fascia, below the line of the gutter, or a green stain on the soffit.

What the damage looks like

Look at the fascia and soffit from the ground. A board that is stained, blistered or peeling above the gutter line has been wet for some time. Timber fascias go soft and flaky, and a screwdriver sinks into the wood. uPVC boards do not rot, but water running behind them soaks the rafter ends, and the rot happens out of sight. The soffit sags or stains, and in the loft you may see damp on the timbers at the eaves.

The wall can take water too. If the run sits proud of the wall, water runs behind the gutter and down the brick, leaving streaks and, over winters, frost damage and green growth. Our page on rotten fascia boards explains how to judge the extent of decay, and why gutters overflow deals with the blocked-channel version.

How it is fixed

The cure depends on the cause. If the felt is short, an eaves tray or a strip of felt is fitted to carry it into the channel. If the gutter is set too high or has tilted, the brackets are adjusted or replaced so the front lip sits below the line of the roof and the back is tight to the board. If the board is rotten, it is replaced before the gutter goes back. A blocked run is cleared and the outlet checked.

Often the sound fix is bigger than a single bracket. A fascia that rots again and again usually has a felt problem, and a new board hung under the same felt will rot in turn. That is why a roofer who simply re-fixes the gutter and paints the board is not solving the fault. The felt line, the bottom row of tiles and the gutter height have to be looked at together. Our page on eaves protection systems explains the parts that keep the edge dry.

Corners are a frequent trouble spot, because they collect the flow from two roof slopes at once. A short felt, a stop end that has dropped or a valley that discharges near the corner can send the overflow behind the channel at that point alone. If only one corner shows the stain, look at what feeds it before blaming the whole run.

Checking your own house

On a dry day, look at the line from the ground. The front lip of the gutter should sit slightly below a line drawn from the tile edge, so water falls into the channel. The felt should be visible draping into the gutter if you look up from below with a torch. The gutter should be level, not leaning outwards. After rain, check the face of the fascia and the wall for a dark streak.

Do not climb to inspect it. Photograph the eaves with a zoom lens, and compare the line of each elevation. A free survey from us includes photographs of the felt line, the tile edge, the gutter height and the fascia. If the cause is minor, we say so. Either way you receive fixed written figures. The guttering, soffits and fascias page covers the service, and replacing fascias without disturbing the roof describes the eaves work.