Age and type of house
A lath-and-plaster ceiling bulges and bits of the plaster key have dropped in the loft. What has the bulge not proved about the joists above it?
The bulge has not proved anything about the joists above it. A lath-and-plaster ceiling bulges, and bits of the plaster key have dropped in the loft. Those keys are the plaster that was pushed through the laths and held the ceiling up. When they break and fall, the ceiling is losing its grip and can sag. The joists that carry the laths are a different member. Debris on the loft floor shows failed keys. It does not show that the joists are rotten, deflected, or undersized. The survey saw a failing ceiling. It did not condemn the floor structure above it.
Last reviewed 24 October 2026. Written for buyers in England and Wales unless this answer says otherwise. No named surveyor has signed this page. It is general guidance, not a report on your house, and not legal advice.
What is the fuller explanation?
Lath and plaster fails in its own way. The laths stay nailed while the plaster nibs snap, and the ceiling bellies between supports that may still be straight. From the loft, the surveyor can see broken keys and the top of the laths. Seeing a joist’s top face, where it was visible, is still not a test for decay in the bearing or a measurement of sag in the timber. The bulge is below, in the plaster. Joist condition needs its own look, and this bulge has not supplied it.
Ask the surveyor whether the joists around the bulge were visible and what they looked like, and treat a ceiling repair as a ceiling repair. If the loft also showed soft timber, that is a separate note and a timber specialist’s brief. Do not price a joist replacement off fallen keys. The inspection recorded a bulge and lost key. It did not prove the joists had failed.
What should you ask your surveyor?
- What of the plaster key had dropped, and where was the bulge?
- Which joists, if any, could you see, and what did they show?
- Did the bulge stop short of a finding about the timbers?
What are the typical next steps?
- Treat fallen keys as a failing ceiling, not as failed joists.
- Ask which joists were actually visible around the bulge.
- Instruct a timber specialist only if the timber itself is in doubt.
Costs vary with the building and with who you instruct. Where this page does not cite a published figure, ask the surveyor, a relevant specialist, or your solicitor for a written quote. Do not treat a forum average as the price.
Also asked about this
If the laths are cracked, have the joists overloaded them?
Cracked laths show distress in the laths. They do not prove the joists above have overloaded, decayed, or sagged. The survey’s finding is a bulging ceiling and plaster keys in the loft. The mechanism in the timber was not demonstrated. Lath damage stays with the ceiling until the joists are looked at for their own sake.
Can the bulge be screwed back without looking at the loft again?
The survey has not specified a screw repair. Keys have already dropped in the loft, which is why the ceiling is bulging. A fixing from below would not prove the joists sound, and the report has not claimed they are. Any repair needs the ceiling understood as plaster that has lost its key, not as a joist verdict.