The short answer
A good roofer plans for rain, so a shower should not soak your house. The roof is stripped and covered in sections, the open area is kept small, and the underlay or sheeting goes over it before the day ends. Heavy rain or high wind can stop work. If water does get in, the contractor who left the roof open is responsible for putting it right, and you should take photos of the damage and report it to them immediately.
How roofers keep a house dry while the old covering is off, what stops a day's work and who pays when water gets in.
Working in sections
Nobody strips a whole roof and then hopes. The usual method is to take off one section at a time, such as one slope or part of one slope, then fix the new underlay and battens before moving on. At any moment, the area open to the weather is small, and a tarpaulin or sheet can be pulled over it in minutes. The forecast is checked each morning, and the day's plan is set to match it.
That plan depends on the roof. A simple gable with two slopes can be done one side at a time. A hip roof, a roof with dormers or a rear extension has more joins to protect, and those joins are where water tries to get in first. The roofer should explain, before the work starts, which area will be opened each day and when it will be made watertight.
The roof is not the only thing left open. Chimney stacks, valleys and the junction with a neighbour's wall all need covering before the roofers leave, and leadwork may need to be redone before the covering can be closed. Our answer on how long a roof replacement takes covers the usual order of work.
Sheeting and temporary cover
A heavy-duty sheet is the first line of defence. It is fixed over the opened section, tied down against the wind and weighted at the eaves so it does not flap or lift. Breathable underlay laid over the rafters also gives some protection, but underlay is not a waterproof roof, and it is not meant to carry a downpour for long. It is held in place with battens, which is why the sequence of strip, underlay, battens and tiles is kept tight.
On larger roofs, or where several days of weather are uncertain, a temporary scaffold roof can be built above the whole house. It is a frame with sheeting stretched over it, and it lets the roofers work through showers. It costs more to hire, so ask at the quote stage whether one is needed, and whether it is part of the single total price.
Inside the house, the main precaution is in your own hands. Clear the top floor and loft of anything you would not want wet, and move beds away from ceilings below the work. A dust sheet in the loft is cheap, and it also catches the grit that falls from an old roof when it is lifted.
When rain stops the job
Some weather is simply too much. Steady heavy rain makes slopes slippery and a wet roof is dangerous to work on, and strong wind can lift loose sheets and tiles. When that happens, the roofers will leave the roof covered and wait. A day lost to weather is not a failure of the job, and it is better than pushing on and working in conditions that put people or the house at risk.
A wet spell can still move the finish date, so ask how delays are handled. We tell the customer what happens each day, including when a day is called off and what has been covered. Scaffold hire carries on during a delay, which is why a clear plan, not a guess at the weather, is worth having. Our answer on replacing a roof in winter goes into the colder months.
Some materials also have limits. Cement-based bedding and sealants need dry surfaces, so ridge and hip details may be left until the weather clears. A dry-fix ridge system can be fitted in a wider range of conditions, since it is mechanically fixed.
Who is responsible for water damage?
The contractor who opened the roof is responsible for keeping it watertight, and section 49 of the Consumer Rights Act 2015 expects reasonable care and skill in any service. Letting a stripped roof flood a bedroom because no sheet was ready is not reasonable care. That puts the repair on the roofer, not on you, but you should still act at once.
Photograph the damage as soon as you can, note the time and tell the roofer straight away. Move belongings out of the way and, if water is running through a light fitting, switch off the circuit and call an electrician. If your home insurance might respond, tell the insurer before anything else, make the damage safe with a temporary repair, and keep photos and receipts. Never take it for granted that a claim will pay out.
The best protection is the plan agreed before the work, in writing, with the same person telling you each day what is open and what is covered. If a dispute does follow, Citizens Advice is the place to start. Our roof replacement page sets out how a whole job runs.
More on this in Roof Replacement & New Roofs in Crawley
Two more rain questions
Should I be at home on a roof replacement day?
You do not have to be, but it helps to be reachable. The roofer may need a decision if rain arrives, such as whether to stop and cover the roof, or whether a bedroom ceiling shows damp. Leave a phone number, clear the rooms below the work, and ask for a short update at the end of each day.
Can new roof timbers get wet without harm?
A short soaking is usually survivable, but sodden timber is a problem if it is then covered and trapped. Roofers should let any wet battens or boards dry before the tiles go on, or replace them. The survey and the plan for each day should say how that is handled, and the photos taken during the job show what was done.