The short answer
Some of it can, most of it should not. Light rain rarely stops stripping or relaying tiles and slates if the roof is covered as the work goes on, but flat roofing, lead work, adhesives, bedding and any job with an open roof need dry conditions. Wind, lightning and slippery surfaces can end a day on their own. When a roof is actively leaking, making it safe comes before anything else, whatever the weather.
Why wet weather is a safety problem first
Roofs are steep, high and smooth. Wet slate, moss, painted fascia boards and lead sheet all become slick in rain, and scaffold boards can ice up or collect a film of mud from boots. A slip at height is the main danger in this trade, and it is why a sensible crew stops when conditions turn rather than carrying on to hit a deadline.
Wind makes it worse. Sheets of underlay, loose tiles and tarpaulin act like sails, and gusts can tear them out of hands or send them across the street. Lightning is a separate hazard: a crew standing on a scaffold with metal poles is the highest thing around. The decision to stop belongs to the person on site, and a customer should never press them to carry on. Our page on doing a re-roof yourself explains why this matters even more for a homeowner without the kit.
Work that can carry on in light rain
Stripping and relaying slates or tiles is the most forgiving job, because the water sheds off a covering that is designed to shed it. A good crew strips only a section at a time, lays underlay and battens straight behind, and fixes the covering before the next section starts. The rain then falls on a roof that has a finished layer at every stage, never on bare rafters.
Light drizzle also does little to hand-fixing or nailing. The limits are practical rather than strict. Wet tiles are heavier and slipperier, so each lift takes more care, and wet nails and clips are harder to handle. If the shower turns to a downpour, the crew covers the exposed area and waits. Nobody can promise a fixed hour for the weather to clear, and a good roofer will say so.
Work that needs dry conditions
Flat roofing is the clearest case. Torch-on felt, GRP resin and single-ply membranes bond to a deck, and a wet deck traps moisture beneath the new layer. That moisture later blisters the covering and rots the timber. A flat roof is built on a dry deck, and no honest roofer lays it on a wet one.
Lead work is similar. Flashings and valley linings are cut, dressed and fixed to dry surfaces, and the adjoining mortar or sealant has to take hold. Mortar bedding and flaunching, the sloped mortar cap around a chimney pot, wash out if rain reaches them before they set. Roof windows and chimney work involve open joints. Our page on removing old roofing felt shows why a flat deck must be inspected before anything goes back on.
How an open roof is kept watertight
The risk with a re-roof is the moment between taking the old covering off and putting the new one on. Good practice is to work in small sections and cover each with heavy-duty sheeting or a temporary tarpaulin, weighted or battened down, when work stops for the evening and whenever a shower rolls in. Forecasts help, but the sky over the Downs can change quickly, so sheeting is kept to hand on the scaffold rather than in the van. Gables, valleys and ridges are the points where the cover is most likely to lift.
Some larger jobs use a temporary roof, a scaffold frame with a sheeted lid that keeps the weather off for the whole project. The house is still an occupied building, so the ceiling, loft contents and insulation need protection too. If you are staying put, our page on living in the house during a re-roof describes what to move and what to expect.
What happens when your roof is leaking in the rain
A roof that is already letting water in is a different case. We put a leak or storm damage ahead of routine work, and the opening move is a make-safe: sheeting the damaged area from above, or protecting the room below, instead of starting the lasting repair. That repair waits for drier weather, because mortar, sealant and flat roof coverings will not cure in the wet.
Meanwhile, if water is dripping through a ceiling, stand a bucket beneath it, shift furniture and electrical items clear and keep away from any bulge in the plaster. Stay off the roof yourself. Photograph the damage, because those pictures help with the survey and with any conversation you have with your insurer. Our page on what causes a roof to fail looks at the underlying causes of leaks.
Rain, insulation and the building rules
Weather also affects what goes into the roof. Insulation placed between rafters has to stay dry, since wet insulation loses performance and can hold moisture against timber. Where a re-roof triggers a thermal upgrade under Part L, the work is planned so each layer goes in dry and is closed in before the next shower; our Part L page sets out when that applies.
This is a reason to schedule larger jobs for a spell of settled weather where you can, and to keep dates flexible. Timing is something we talk through during the survey, before the written quote arrives, and a start date is only a plan until the weather agrees. A written guarantee on our workmanship lasts 10 years, and no rubbish is left behind. For the full process, see our roof replacement page, or phone 01793 626096 to discuss your own roof.