The short answer
Keep everyone out from beneath the bulge and switch off the power to that area at the consumer unit if you can reach it safely. If it is safe, release the water in a controlled way into a bucket by piercing the lowest point with a screwdriver. Then have the roof made safe, because a ceiling that has filled once will fill again at the next downpour.
Why the ceiling bulges and why it is dangerous
When rain gets through the covering, it lands on the loft insulation and the plasterboard below. The board is porous and holds a surprising amount before it fails. The water gathers at the lowest spot between joists, and the board stretches into a dome. A bulge the size of a dinner plate can hold litres, and water is heavy.
The danger is the ceiling giving way. Wet plasterboard loses its strength, the paper face tears and the contents drop together, bringing plaster, insulation and sometimes timber with them. Risk rises under a light fitting, since the fitting adds weight and water can reach the wiring. Older lath-and-plaster ceilings behave differently again, because the plaster keys can let go in one slab.
Warning signs worth taking seriously include a ceiling that looks lower than it did, a crack that opens along the line of a joist, drips falling from several points, or a sound of trickling above the board. Any of these means the load is growing, so leave the room until the water has been released.
Making the room safe first
Move people and pets out of the room and shut the door. Shift furniture and valuables well away, and lay plastic sheeting or old towels over the floor. Do not stand underneath the bulge, and never place a ladder under it.
Wet plaster near any lamp, rose or socket means that circuit should be treated as live and dangerous. Turn it off at the fuse board only when your route to it stays dry. If it does not, keep away and phone an electrician; a spot of delay costs far less than a shock. Never touch a switch with wet hands, and do not use a vacuum or fan in the room until an electrician has said it is safe. Our page on leaks near electrics explains how to stay safe while the water is still moving.
How to drain it in a controlled way
If the bulge is nowhere near electrics and you can stand to one side, you may release the water yourself. Set a bucket or washing-up bowl under the lowest point, with a sheet of plastic spread wider than the bucket to catch splashes. Using a screwdriver held at arm's length, pierce the lowest point of the dome. Water will run out in a stream, so keep a second bucket ready and step aside as it drains.
Wear eye protection if you have it, since dirty water and flakes of plaster can fall with the flow. Expect more than one bucketful: water often keeps arriving from the insulation above for several minutes. Once it slows, leave the hole alone and do not try to patch it, because the board around it is soft and will not take filler.
Draining by hand is a short-term safety measure, not a repair. It prevents a sudden collapse and protects the rest of the ceiling. If you are not comfortable doing it, or if the plaster is already cracking, stay clear and ask for help. Take photographs before and after, for your own records.
Getting the roof made safe
The water came from somewhere. Once the dome is drained, the leak has to be found and stopped. It might be a slipped tile, failed flashing, a blocked valley, a gutter overflowing into the eaves or a split in a flat roof. Stopping water coming in is our first task on any call about a leak, and that may mean a temporary cover or patch while we plan the proper repair.
Photographs arrive with the quote, which lets you see the fault for yourself. Our preference is a measured repair, and if the leak is part of a larger problem we say what and why, then lay out the choices. Our guide to emergency roof repairs sets out how that works from first call to finished work.
Photographs, insurance and the order of events
If you are thinking of a claim, photograph the bulge, the stain, the drained water and the loft before anything is moved. Our page on photos for a roof claim lists what is worth capturing. Contact your insurer early, and keep receipts for buckets, sheeting and any temporary work.
Storm Eunice advice from the ABI in 2022 was to arrange emergency work if it is needed to stop damage growing, after speaking to your insurer. If you are unsure whether to repair before claiming, the page on repairing before a claim explains the order. We cannot promise any claim will be accepted, and we do not handle claims.
Drying out and repairing the ceiling
Once the roof is sound, the ceiling has to dry. Open windows when the weather allows, run a dehumidifier and keep the loft ventilated. Wet insulation above the board should be lifted and dried or replaced. Plasterboard that has stretched or lost its face should be renewed, because it will not regain its strength. A damp ceiling left alone can grow mould within days and may stain through fresh paint.
Stained but flat plasterboard can sometimes be sealed and redecorated after it has dried fully. Check with a plasterer first. The kinds of damage that cause leaks in the first place are listed on our page on storm damage types, which helps you judge whether the same fault could return.