The short answer
A roof can sometimes be made safe in the rain, but a lasting repair usually needs dry conditions. Covering the damaged area, clearing a blocked gutter or fixing a slipped tile from a safe position may be possible, while mortar, adhesives, sealants and felt work need a dry surface to bond. In wet weather the sensible plan is a temporary cover straight away, with the proper repair done after the slope has dried out.
What a roofer can and cannot do while it rains
Work divides into two kinds: stopping water, and mending the fault. Stopping water is the priority when rain is already getting in, and it can often be done from a safe position with a battened tarpaulin, a lead or membrane cover over the opening, or a replaced slate that clips in without mortar. Mending the fault is a different matter. Re-bedding a ridge, repointing a chimney, bonding a flat roof patch or dressing a lead flashing into new mortar all rely on surfaces that are clean and dry.
So the realistic answer for a leak in a storm is a make-safe now and a proper repair after. We say that plainly at the first call rather than promise a finished job in conditions where one cannot be done properly.
Why some materials need a dry day
Water is the enemy of every bond on a roof, and the reasons differ by material. Sand and cement mortar will not key to a wet tile or brick face, and the first shower after it is placed can wash the mix out of the joint. Bitumen felt is joined with heat, and a damp deck turns to steam under the torch. EPDM, the synthetic rubber membrane used on flat roofs, and GRP (glass-reinforced plastic, or fibreglass) both rely on adhesives or resins that fail to cure properly in wet air. Most sealants and mastics are also unreliable on a wet substrate.
Why the temperature matters too
A repair that looks finished can still be weak if it was laid on damp ground. Mortar placed in the wet may look sound for a week, then crumble at the first frost, and a sealant smeared over a wet crack hides the fault without closing it. That second kind of repair is a frequent reason a leak returns.
Cold slows curing as much as damp does. Frost on a surface can look like moisture and has the same effect, which is why our page on roof repairs in winter and wet weather deals with planning around the season.
The safety side of working on a wet roof
A wet slate or clay tile gives very little grip, and a film of moss on stone or tile makes the surface worse again. Wind in a shower matters as well, because a sheet of tarpaulin catches it. No roof repair is worth a fall, and a roofer who is asked to climb onto a wet pitch should say no, or find another way in: from inside the loft, from a tower or from scaffold.
Access is therefore part of the decision. A low single-storey slope with a ladder and a crawl board is a different job from a three-storey terrace with a tower to put up first. Whether any of this is worthwhile in the wet is explained in our answer on scaffolding for roof repairs.
What you can do yourself while you wait for dry weather
If the forecast is poor for days, ask what the temporary measure is made of and how it is held down. A good one is battened or weighted so that wind cannot lift it, and it overlaps the slope above the damage so that water runs over it rather than beneath. Ask also for photographs of it in place, as a record for later.
Rain also changes what the survey can show. A roof in the wet makes some faults obvious, because water runs where it should not, and hides others, because every surface is dark and shiny. We often look from inside the loft during a shower, watching where daylight, drips and damp timber line up, then return to the slope when it is dry to confirm the exact tile, joint or flashing responsible.
Work from inside and keep your feet on the floor. Move furniture and rugs from under the drip, stand a bucket or a baking tray under the drip, with a folded towel inside to stop splashing. If the ceiling is bulging with trapped water, a small hole made carefully with a screwdriver lets it drain into a bucket rather than collapsing. Leave the roof alone, and keep clear of lights and sockets near the leak.
If a tree or a branch has hit the roof in the same weather, the picture changes: there may be structural damage, and our page on what to do when a tree hits your roof sets out the order of things. Take photographs of the damage for any insurance claim, dated, before anything is moved or binned.
How we handle a call during a storm
An active leak is dealt with ahead of routine work, and the first aim is a roof that stops admitting water. That may mean a temporary cover now and the lasting repair on a later visit, with the two stages described separately so you can see what each one is for. The written quote follows the survey, and the repair itself is covered by our workmanship guarantee in writing once it is finished.
For a full picture of the jobs we do on pitched and flat roofs, see our roof repairs page, or ring 01453 933613; WhatsApp and the form on this page reach us as well.