Most cracks in ceiling plaster are cosmetic. Hairline cracks and fine cracks a millimetre or so wide usually come from small movements in the building, joints between boards, or new plaster drying out, and they can be filled and painted. A crack that is wide, growing or sitting next to a sag in the ceiling should be looked at before anyone fills it.
Which ceiling cracks are normal?
Cracks up to about 5 mm wide are usually cosmetic, unless they run diagonally from a door or window, are wider at one end or keep growing. BRE, the building research body, has a scale for cracks in house walls that treats them as "aesthetic" issues needing only redecoration. Its summary Assessing cracks in houses explains the six categories of its Digest 251, and Designing Buildings lists the width for each.
| Crack width | What BRE's scale for walls suggests |
|---|---|
| Hairline, under about 0.1 mm | Category 0, no repair needed |
| Fine, up to about 1 mm | Category 1, dealt with by normal decoration |
| Up to about 5 mm | Category 2, easily filled |
| About 5 to 15 mm | Category 3. BRE groups 3 and 4 as serviceability issues, affecting weather-tightness and how doors and windows work |
| About 15 to 25 mm | Category 4, extensive damage |
| Over about 25 mm | Category 5, a stability issue likely to need structural work |
BRE says its summary is a simplification, that whether a crack is widening over time can change the grading, and that Digest 251 itself should be used for a proper assessment. The scale was written for the walls of low-rise buildings, so treat it as a rough guide for ceilings.
What do different crack patterns mean?
The pattern often points to the cause.
| Pattern | Usual cause |
|---|---|
| Straight lines in a grid, along board joints | Plasterboard joints that were not taped, fully filled or supported. British Gypsum's finishes guidance says failing to fully fill a joint can cause it to crack. See cracks in new plaster |
| A line where the ceiling meets the wall | Two surfaces moving slightly differently. Usually cosmetic |
| A web of fine cracks on an old ceiling | Old lath and plaster moving with the timber behind it. See our guide to lath and plaster |
| A crack with a brown stain | Water from above. Find the leak first; our guide to painting a ceiling after a leak covers what follows |
| A crack with a sag or bulge | Plaster coming away from what holds it up, or a structural problem. Get it checked |
When should a ceiling crack be checked by a professional?
When it is wide or growing, or comes with other signs of movement:
- it is wider than about 5 mm
- it runs diagonally from the corner of a door or window, even if it is narrow
- it is getting longer or wider, or comes back soon after filling
- the ceiling sags or bulges beside it, or a patch has sounded hollow when decorated
- doors in the room, or on the floor above, have started to stick
- there are matching cracks in the walls
Any of these is a reason to ask a structural engineer or a chartered surveyor. BRE advises consulting a building professional where damage is significant. An engineer may want to measure a crack over several weeks to see whether it is still moving. If a ceiling is sagging, keep people out from under it until it has been looked at.
Could a crack in the ceiling mean subsidence?
Not usually on its own. The Association of British Insurers says the first sign of subsidence is usually cracks in the walls, which appear suddenly, "especially after long periods of dry weather". It describes them as diagonal, "wider at the top than at the bottom", "thicker than a 10 pence coin" and "found around doors and windows", with doors and windows that stick for no obvious reason. It adds that clay soils "shrink, crack and shift during hot, dry weather", and that trees or large shrubs close to the house can dry the soil out further.
If you suspect subsidence, the ABI's advice is to "contact your insurer as soon as possible". It explains that the insurer may send an engineer and that the movement may be monitored for a while before repairs. Take dated photos with a ruler beside each crack, and speak to the insurer before any filling or redecorating.
What should you do if a ceiling is bulging with water?
Keep everyone out from under it, then deal with the water and the electrics. A ceiling holding water is heavy and can give way.
- Turn off the water at the stopcock. If the water is coming from a flat above, tell that neighbour and the landlord, freeholder or managing agent straight away.
- If water could reach a light fitting or other electrics, switch off at the consumer unit, but only if you can reach it with dry hands and without standing in water or under the bulge. If you cannot, leave it and call a registered electrician. In its flood advice, Electrical Safety First advises switching off "if it is safe to do so", and calling a registered electrician if there is "any sign of water inside the consumer unit/ fusebox".
- Leave the power off until a registered electrician has checked it. Electrical Safety First says supplies "should not be turned back on until professional advice says it is safe".
- Put buckets only under drips you can reach without standing under the bulge, and keep them away from light fittings. Move what you can from the edges of the room, take photos and tell your insurer.
- Do not poke, pierce or drain the bulge yourself, especially near a light fitting. Leave that to the plumber or a contractor sent by the insurer.
Once the leak is fixed and the ceiling has dried, our guide to painting a ceiling after a water leak covers what comes next.
How is a fine ceiling crack repaired?
For a fine crack with no sign of movement, the crack is opened slightly, filled, sanded and the whole ceiling repainted so the repair does not show. On a plasterboard ceiling where the joints are cracking, the joints may need to be taped again.
If the ceiling has a textured coating applied before the UK asbestos ban in 1999, do not open up, sand or scrape the crack. Lambeth Council's guide says it is always safest to assume such coatings contain asbestos, that disturbing them or leaving them in poor condition can cause a health risk, and that damaged coatings need advice before painting. Our guide to asbestos surveys before refurbishment explains what to ask for.
Vayton repairs and redecorates ceilings. Where a crack points to movement in the structure, we ask for an engineer's view before quoting for the repair.
Send us a photo of the crack with a ruler held next to it, and tell us how long it has been there. We reply within one working day. Send a photo of the crack.