Gutter Leaking at a Joint

Why do gutter joints start leaking?

Most gutters on UK houses today are PVC. Lengths are joined by a union bracket: a clip with a rubber gasket that the two gutter ends sit into. The gutter is not glued, because PVC grows and shrinks a surprising amount between a hot summer roof and a frosty night. The joint lets it slide while the gasket keeps it watertight.

That design gives you the usual causes, roughly in order of how often they turn out to be the answer:

• A blockage downstream. Leaves, moss and roof grit build up, water pools, and the joint is the first place it gets out. The seal may be fine.
• A perished or dislodged gasket. After years of sun and frost the rubber hardens and cracks, or it has slipped out of its groove.
• The gutter has pulled out of the bracket. Union brackets have insertion marks inside; if a length was cut short or fitted past the mark, it drops out of the seal in cold weather. Leaks that only show in winter point to this.
• Wrong fall or a sagging bracket. A gutter that dips at the joint holds a standing pool on the seal.
• Mixed profiles. Half-round, square and ogee gutters from different makers look alike but do not seal together.

When a gutter leak becomes an emergency

A drip onto a path is a nuisance. It becomes urgent when the water is going somewhere it should not: running down the brickwork into an airbrick, soaking through a window reveal, or pouring onto a flat roof or into a basement lightwell. A damp patch that appears inside on an upstairs wall after rain and dries out in between is often an outside gutter or downpipe, not an internal pipe.

If water is coming through a ceiling or wall inside, you need to know whether it is rain or supply water, because the fix is completely different. Run this check: does the patch grow only during and after rain? If it also grows on a dry day, or your water meter moves with every tap off, the source is a pipe. See signs of a hidden water leak for how to tell. For water already coming through a ceiling, our ceiling leak repair visit is the £60 call-out at any hour, and the repair price is agreed with you on site before any work starts.

Only work on a gutter from a ladder if it is a single-storey height, the ladder is footed by a second person and the ground is firm and dry. For first-floor gutters and above, use someone with a tower or access equipment. Never lean a ladder on the gutter itself.

Diagnose it in the right order

Go out during rain, or run a hose into the high end of the gutter on a dry day, and watch the joint. Then work through these steps before buying anything:

• Look along the whole run from a window or the ground. Plants growing out of the gutter, or water overflowing the front lip near the joint, mean a blockage.
• Scoop the gutter clean from the joint to the outlet and flush the downpipe with a hose. If water backs up out of the top of the downpipe, the blockage is lower down, sometimes at the gully at ground level.
• Check the fall. Gutters need a slight slope towards the outlet. If water sits in a pool either side of the joint, a bracket has sagged or snapped.
• Check the ends sit fully in the union bracket, up to the insertion marks.
• Only then look at the gasket. Run a finger along it: hard, cracked or missing rubber means the bracket needs replacing.

Fixing a leaking PVC gutter joint

The lasting fix for a failed gasket is a new union bracket of the same make and profile. Take a photo of the gutter end and any maker’s name moulded on the bracket before you go to a builders’ merchant. Unclip the old bracket (they snap off the gutter lip), clean the gutter ends with a scourer and soapy water, and clip the new one on, sliding the ends in to the marks. A matching bracket is an inexpensive part.

If a length has shrunk short of the bracket, a new bracket will not help; the gutter needs refitting with the correct lengths, or an extra length adding. Where you cannot find the same profile, adaptor unions exist for common changes between makes, though a patchwork run rarely stays tight for long.

As a stopgap, a gutter sealant made for PVC, or a strip of butyl gutter repair tape laid across the joint on the inside, will hold through a spell of wet weather. The surface must be clean and completely dry, which in practice means waiting for a dry day. Ordinary bathroom silicone does not bond well to old, chalky PVC and usually peels within months.

Cast iron and metal gutters

Many Victorian and Edwardian London houses still have cast iron gutters. Their joints are a spigot and socket held with a small nut and bolt, with sealant or putty between the two ends. They leak when the bolt rusts through or the old sealant dries out. The repair is to unbolt the joint, clean both faces back to sound metal, apply fresh gutter sealant and fit a new galvanised bolt. A cast iron length is heavy and brittle, so do not lever on it; a snapped section needs a specialist.

Aluminium gutters are sealed with sealant at their joints too and are resealed the same way. On a listed building or in a conservation area, check before swapping metal for plastic, because a change of material can need consent.

Who fixes a leaking gutter?

Gutters are usually a job for a roofer or a gutter specialist rather than an emergency plumber. Where a plumber is useful is when the leak is not in the gutter at all: a downpipe that discharges into a blocked gully and floods back against the wall, an overflow pipe from a cold water tank or a boiler overflow pipe dripping outside that looks like a gutter drip, or water inside the house that needs tracing to a pipe.

If you rent, gutters and downpipes are part of the structure and exterior, which sits with the landlord. In a block of flats they are usually the freeholder’s or managing agent’s responsibility; the lease confirms it. Report it in writing with photos, especially if water is reaching inside. If the damp has already got in, a water leak inside a wall explains how to tell rain penetration from a pipe leak.