Question answered
Leaking garage roof: repair or replace?
The short answer
Repair a leaking garage roof when the leak comes from one failed spot, such as a split in the felt, a lifted edge or a loose sheet joint, and the deck beneath is dry and sound. Replace it when there are many faults, the covering is old, or the boards are soft. A cement-sheet roof on an older garage should be checked for asbestos before anyone touches it.
Most garage roof leaks come from a small number of places, and many can be mended. The question is whether the roof around the fault has enough life left to be worth mending.
Finding where the water comes in
The stain inside is rarely beneath the hole outside. On a flat roof, water can enter at one point and run along the deck or a rafter before it drips, so the spot you see may be a metre from the fault. On a sheet roof it can track down a purlin or along a lap.
The usual suspects are few. On felt they are splits and blisters, laps that have opened, the upstand against the house wall, and the edges where the covering turns down. On sheets they are the joints between them, the fixings, cracks and the ridge. On both, the gutter, a blocked outlet or a flashing against a neighbouring wall can send water in at the edge.
Our survey starts indoors, following stains and damp timber up to the fault, then compares what we find with the outside. You get photographs of your roof first, then a written quote giving a single figure. Where water is coming in now, making the roof safe comes first.
Stay off the roof if you do not know what it is made of. How to tell if a garage roof is asbestos explains why.
When a felt patch is the right fix
A patch is the smallest job that can fix a single fault. A split along a lap, a blister that has cracked, or a torn edge can be cut out, dried and covered with a new piece of felt, stuck down and sealed so that the repair sheds water in the same direction as the original.
Patching works when three things hold. The felt around the repair must be sound enough to bond to. The deck underneath must be dry, because new felt over damp boards traps the moisture. And there must not be a string of other faults waiting, since a patch shifts the stress to the next weakest point.
A coating of bitumen or a liquid sealant can buy a season or two on a roof that is otherwise fine, but it is not a substitute for finding the cause. Smearing sealant over a split hides it and often lets water in underneath. MyBuilder's roof repair guide (updated 21 August 2026) puts minor repairs at £100 to £300 in typical UK terms, a useful comparison against replacement. See how long a garage roof lasts to judge how much life is left.
Sheet joints, fixings and cracked panels
Corrugated and flat sheets keep water out by overlap, and the overlaps are where they leak. Sheets can shift in the wind, fixings loosen and rust, washers perish, and the sealing strips between laps harden. A sheet cracked by a fallen branch or by someone standing on it leaks straight through.
The first question on an older garage is what the sheets are. If the garage was built or refurbished before 2000, HSE advises assuming there is asbestos in it, and a leak is not a reason to drill, scrape or screw into the sheets to seal them. That can release fibres, and HSE calls roofs of this kind fragile throughout. Have the material identified first, as testing a garage roof for asbestos describes.
On a modern metal or non-asbestos fibre-cement roof, repair is more straightforward: refit fixings with new washers, renew the lap seals, replace a cracked sheet like for like, and refix the ridge. Where a roof has been patched repeatedly, a new covering often costs less over time than another visit.
When replacing makes more sense
Replacement is the better call when the leak is a symptom rather than an event. Signs include several faults at once, felt that cracks when lifted, ponding water that stays after rain, a covering at the upper end of its typical life, or a deck that is soft, black or spongy underfoot.
Repeated repairs also add up. If you have patched the same roof in two winters, you have paid for the repair twice without fixing what is making it fail. A new covering on a sound deck resets the clock. Our garage roof replacement page shows what that involves; a good flat roof job is laid with a proper fall, with trims and upstands done to last. Our page on EPDM for a garage roof looks at one option, and on a pitched garage the pitched garage roof page explains the alternatives.
If the leak is old, the timber is the thing to check. Rot in the deck or the joists turns a covering swap into a larger repair, and it is better found in a survey than discovered halfway through a job. How long the work takes is covered in how long a garage roof takes.
Limiting damage until the roof is fixed
Move anything water would spoil away from the stain and cover valuables. Put a tray or bucket under a steady drip, and check it after rain so it does not overflow.
Stay off a wet or windy roof.
If a leak is near electrics, such as a light, socket or consumer unit, switch the circuit off at the board and keep clear. A temporary cover can sometimes be fitted to stop water getting in until a proper repair is possible, and we prioritise leaks. Take photographs of the stain and the date, since they help whoever traces the fault and any insurer you speak to. Insurers often exclude gradual damage, so check the policy wording before work starts.
Garage roof leaks: two more questions
Can I just paint a sealant over the leak on my garage roof?
It might hold briefly, though seldom for long. Sealant over a split or open lap covers the symptom and can trap water beneath, so the deck rots unseen. Do not apply anything to sheets on an older garage until you know whether they contain asbestos.
Why does my garage ceiling only drip after long spells of rain?
Often the fault is small and the water has a long path. After days of rain the deck or insulation soaks up what it can and then lets go. A lifted lap or a gutter overflow can behave this way. Tracing the water back is how the true entry point is found.
Tell us about your roof
Describe what is happening and we will call you back to arrange a visit.
- Photographs of what we find
- A written quote with one total price
- Or call 01903 299063
10-year workmanship guarantee, in writing.