The short answer
A gutter fault shows outside and during rain: water sheeting down a wall, dripping from a joint, or spilling over the front edge. A roof leak shows inside, often a while after the rain starts and sometimes hours after it stops, as a stain on a ceiling or damp in the loft. Both can exist together, so check each in turn.
Watching the water when it rains
The easiest test costs nothing: stand outside in steady rain and look. Water that pours over the front lip of the gutter, drips from a joint, or runs down the wall beneath a downpipe is a gutter problem. The gutter is the channel along the eaves, and its job is to carry roof water to the drain. If it cannot, the water goes wherever gravity sends it, and that is often straight down the face of the house.
Look at the brickwork or render below the gutter line, and at the underside of the soffit, the flat board beneath the overhang. Damp or peeling paint there is another giveaway. A dark vertical streak, green algae or a patch of flaking paint beneath a joint tells you the gutter has been leaking for a while. Inside, the same fault tends to show as damp on an outside wall near the ceiling, in the corner nearest the downpipe, rather than in the middle of a room.
Signs that point to the roof itself
Roof leaks behave differently. Water gets in through a cracked tile, a displaced slate, lifted lead beside a chimney or a tired valley lining, then creeps down the rafters and over the underlay before it finally drips. That journey can take a long time, so a stain may appear well away from the hole and may keep growing after the rain has stopped.
Check the loft with a torch. Dark patches on the underside of the tiles, damp insulation, or water tracking along a timber point upwards. Daylight showing through the covering is a sure sign of a gap, and so is a tile that sits visibly lower than its neighbours. Water marks that run in a line along a rafter show the path the leak is taking, and the highest mark is the best guide to where it enters. Stains on a ceiling in the middle of a room, around a chimney breast, or under a roof window usually come from the roof, not the guttering.
Our page on lightning damage to a roof describes one unusual way coverings are disturbed, and snow damage to a roof covers another.
Gutters that cause what looks like a roof leak
The two faults overlap more than people expect. A blocked gutter fills with leaves and silt, water backs up against the fascia board, and the overflow soaks the eaves timber and the end of the rafters. It can also push behind the bottom row of tiles. The stain then appears high on an external wall, and it looks like a roof problem even though the roof covering is sound.
Sagging runs cause similar trouble. A run of gutter has to slope slightly towards its outlet, and manufacturers typically recommend roughly 1:600 to 1:350 depending on the system. If brackets have loosened, the fall reverses, water sits in pools, and the joints open under the weight. Gutters on old houses are often cast iron, and rusted joints weep long before the metal fails entirely.
A simple way to tell which it is
Try this on a dry day with someone to help. Ask them to run a hosepipe on the gutter alone, with the roof slope kept dry, while you watch the inside of the house and the loft. If damp appears, the gutter or the eaves are leaking. Then run the hose on the roof slope above the suspect area, starting low and working upwards in stages, pausing a few minutes at each stage. Water that arrives inside after the second test points to the covering.
Go slowly and never hose upwards under tiles. Do not climb to do either test. If the stain is wet right now and a ceiling is bulging, the page on what to do about a roof leak comes first.
What each fix involves and costs
Both kinds of fault are cheaper to deal with early, because a gutter that keeps overflowing soaks the fascia and a roof that keeps leaking soaks the timbers. Rot in either is dearer than the original repair.
Gutter repairs are usually straightforward: clearing the run, refitting brackets to restore the fall, replacing a split joint seal, or renewing a section. MyBuilder's guttering guide, updated in August 2026, gives gutter replacement as £30 to £70 per metre. Where scaffolding is needed it pushes the total up, and MyBuilder quotes around £850 to £1,200 for a standard two-storey house.
Roof repairs vary far more. MyBuilder's repair guide, updated in August 2026, bands a minor repair at £100 to £300, a moderate one at £500 to £1,000 and a major one at £2,500 or more. Those are national figures, so budget from the written quote that follows a visit to your own roof.
Nearby damage is worth bearing in mind too. If hail, a neighbour's loose tiles or a lightning strike is behind the trouble, hail damage to a roof and damage from a neighbour's tiles may help you work out who should pay.
Getting a firm answer
If the hose test is inconclusive, a survey settles it. We climb up, follow the water from the eaves to the ridge, and send photographs showing exactly what is wrong, whether that is a split gutter joint or a cracked tile. We put forward the lightest repair that truly cures the problem, written down with the total price. Workmanship is guaranteed for 10 years, also in writing. Message us on WhatsApp, ring 01793 626096, or use the enquiry form, and our emergency roof repairs page explains how leaks are prioritised.