Why is your ceiling sagging?

So first things first… What causes a sagging ceiling?

The short answer is that some of the fixings holding the plasterboard sheets to the ceiling timbers have started to fail. Plasterboard ceilings are generally fixed with a combination of stud adhesive and either nails or screws.

Poorly fixed plasterboard

Its quite common for poor work practices in the fixing of plasterboard sheets to result in a ceiling that doesn’t last as long as the rest of the building. And unfortunately its impossible to tell if the sheets have been fixed correctly until it starts to fail. The reason for this is that the strength of the whole system relies on the correct use of stud adhesive…which is impossible to check once the ceilings are up. Each 6 metre ceiling sheet weighs over 50kg and without the holding power of correctly applied stud adhesive, the screws or nails are unable to hold the weight over an extended period of time.

As soon as one nail or screw fails or ‘pops’ through the surface of the plasterboard it puts more weight on the screws/nails around it until they in turn fail and you begin to see noticeable sagging effect in one or more areas of the ceiling. This is your ceiling slowly coming down.


As well as poor fixing practices another major contributor to a sagging ceiling is moisture.

Plasterboard is essentially a core of chalk between 2 layers of paper. Once the paper gets wet or damp it loses its rigidity and strength. Its a building material that must be kept as dry as possible over the life of the building.

Moisture in a ceiling can be caused by 2 main problems. The first is water penetrating the roofing when it rains through a damaged or poorly sealed roof. The second through condensation.

If there is roof leak and large amounts of water coming through a roof leak it is usually obvious immediately and can be rectified…including replacing or repairing an area of plasterboard ceiling if needed.

Sometimes a bigger problem occurs if there is a smaller leak or condensation issues due to lack of sarking or poor roof ventilation. When this happens the problem can evolve slowly over time so that it is almost impossible for a homeowner or tenant to notice a problem until the problem is more widespread and harder to correct.

If a sagging ceiling is caught in time it can be possible to re-screw the affected areas and repaint. If left too long the sagging plasterboard adopts the bowed shape and cant be refixed. When it gets to this stage the only option is to replace the ceiling with a new one.

Some other issues that place added pressure on ceiling fixings is applying extra weight to the ceiling with stored boxes etc in the roof space and the suction effect that occurs in some areas like garages when external doors are opened and closed.

A ceiling that starts sagging is usually due to a combination of reasons and should be assessed by someone with experience in this specific area of the plasterboard trade.