Why Is My Roof Leaking After Heavy Rain in Runcorn?

Two Different Weathers, Two Different Faults

This is the single most useful distinction in diagnosing a leak, and it costs nothing to make.

Wind-driven rain arrives more or less horizontally from one direction. It tests the covering and the details on that face - laps, verges, flashings, exposed edges. A leak that only happens in a gale, from one direction, is a covering or detail problem.

Prolonged heavy rain is vertical and it is about volume. It tests whether the water can get away fast enough. A leak that appears after it has rained hard for hours, regardless of wind, is a drainage problem.

They are different faults in different places, and a great many roofs pass one test and fail the other.

The Four Things That Overflow

Gutters. The obvious one and the commonest. A gutter that is blocked, sagging or has a failed joint overflows at that point, and the water then runs down the fascia and the wall behind it. From inside, that shows on a wall rather than a ceiling - a vertical damp strip, or staining at the top of an upstairs wall.

Valleys. A valley carries the run-off from two slopes into one narrow channel. If it is partly dammed with debris, or if the tiles either side were cut too tight when the roof was laid, it copes with ordinary rain and overflows sideways under the tiles in a downpour - entering the roof several courses above where anybody would look.

The back gutter behind a chimney. The lead channel on the uphill side of a stack, which has to catch everything coming down the slope above and take it round both sides. Silted or formed too shallow, it overflows backwards into the roof. Invisible from the ground.

Flat roof outlets. On the flat and shallow-pitched roofs Runcorn has so many of, a blocked outlet holds water at exactly the point where the covering has joints.

Water Going the Wrong Way Behind a Gutter

Worth its own mention because it is so frequently misdiagnosed as a roof leak.

Water coming off the roof should land in the gutter. If the gutter has dropped, or if the underlay at the eaves does not carry over into it properly, the water lands behind the gutter instead and runs straight down the top of the wall.

From inside that produces damp at the junction of ceiling and external wall, in a room directly under the eaves - which looks exactly like a roof leak and is a twenty-minute job at the eaves.

It is also the reason a rotting fascia is worth taking seriously. A fascia that has gone soft under an apparently sound roof usually means water has been going behind the gutter for years.

What to Do Before Calling

Note whether it was windy or simply raining hard for a long time. That one answer sends us to opposite parts of the building.

Note whether the damp is on a ceiling or on a wall. Ceiling generally means the roof; a vertical strip on a wall generally means drainage.

Look at the gutters during heavy rain, from the ground, from a window, from the garden. Water pouring over the front edge of a gutter, or a curtain of water at one joint, is the diagnosis right there.

And look at the downpipes. Water splashing out of a joint, or a downpipe that is dry while the gutter is overflowing, tells you where the blockage is.

Why This Is Good News

Because most of it needs clearing rather than repairing.

A blocked gutter, a silted valley, a leaf-packed back gutter and a blocked outlet are all obstruction rather than failure. Nothing has broken. Once it is clear, it stops.

That is the cheapest outcome in roofing and it is a meaningful proportion of the heavy-rain calls we take. We look at the rainwater goods on every repair inspection whether or not anybody asked us to, for exactly that reason.

It is also why yearly clearing - after leaf fall, before winter - is the best-value preventive job on any roof. It is not a job to do off a ladder, because reaching along a gutter means leaning, and leaning off a ladder is how people fall.