Why is my ceiling sagging or bulging?

A ceiling sags for one of three reasons, and the first thing to establish is whether there is water involved — because a water-filled ceiling can hold many litres and will come down all at once.

Safety

What you'll need

• A torch
• A bucket and sheeting
• A long screwdriver, for a controlled drain
• Access to the space above, if there is one

Step by step

1. Clear the room and keep people out.Furniture out if you can do it safely, and nobody underneath. This is the whole of the first minute.
2. Establish whether it is wet.A dark stain, a domed bulge, water dripping, or a damp smell. A wet bulge is the urgent case because it is holding weight that increases by the minute.
3. Stop the water first.Turn off the stopcock, or the heating system, or whatever is above. A leaking bath, a burst pipe, a failed tank, or a roof leak are the usual sources.
4. Drain a water bulge deliberately.Bucket beneath, standing to one side and not underneath, and pierce the lowest point of the bulge with a screwdriver on a long handle. Releasing it in a controlled way is far better than letting it fall.
5. For a dry sag, tap around it.A hollow drumming sound over a wide area on an old ceiling means the plaster keys have broken and the plaster is hanging on friction alone.
6. Look above if you can.From the loft or the room above, look for a missing joist hanger, a partly removed wall, a heavy load, or stored items resting directly on the ceiling.
7. Check whether it is spreading.Mark the edges of the bulge with a pencil and the date. A sag that grows over days is an emergency; one that has been there for years is still a problem but not a tonight problem.
8. Consider what is above.A bathroom, a loft full of boxes, or a water tank all change the urgency considerably.
9. Support it temporarily if you must.A sheet of plywood on adjustable props spreads load and buys time. It is a holding measure, not a repair, and it needs doing carefully.
10. Get the right person.A plumber for the leak, a plasterer or builder for a failed lath and plaster ceiling, a structural engineer if a joist or a support has failed.
11. Expect the ceiling to come down.A genuinely sagging plaster ceiling rarely gets pushed back up. Taking that section down and replacing it is normally the honest outcome.
12. Deal with the cause before rebuilding.Dry the structure fully after a leak, and check the joists and the fixings above before any new ceiling goes up.

Tips

• Photograph everything before touching it, including from the room or loft above. Insurers will want it and it is easy to forget in the moment.
• If the ceiling is wet and you have downlighters, treat them as live and dangerous. Water and light fittings are a genuinely serious combination — isolate the circuit.
• A ceiling that has sagged very slightly over decades and is completely stable is common in old houses. The dangerous ones are the ones that changed recently.

Common mistakes

• Pushing the bulge back up — Pressure from below breaks the remaining keys or the remaining plasterboard fixings and can bring the whole section down onto you. A bulge is telling you the ceiling is already barely attached.
• Letting a water-filled ceiling drain itself — It comes down as one saturated slab, with all the debris and insulation above it, over the whole room. A controlled release into a bucket through a small hole limits the damage enormously.

If it doesn't work

Questions people ask