Bulge in ceiling?

[Hebjgghko8u]

Our ceiling downstairs was never very even, it gently goes up and down. But I think there is a slight dip near the corner next to the flat roof. I can't be sure it's new but now not sure what to look for to see if it's the start of a problem. The angle of our lighting has changed and so might be why I've just noticed it.

The ceiling feels hard and normal, there is not discolouration and when we tap it (plasterboard) it sounds hollow. Does this all indicate just an unevenness that I have seen before or could it be more serious?

It's likely just pulled away from the supports. The issue is getting to grips with the cause. It might just be down to vibration or there might e a leak.

If we needed some help to investigate, who would you be calling? Or how might you investigate the cause yourself?

The other thing is there are no cracks

Be really careful. One of my ceilings started sagging. It shortly collapsed. Could have been very serious if anyone/ dog in there. Get it checked asap and don’t sit under in the meantime

Reliable builder. Surveyor? Although that would cost more

As in the whole ceiling bobs up and down!? How old is the house? The plasterboard will sound hollow as you have a cavity there. If you mean your ceiling is wavy rather than moving then less of a concern I suppose unless it’s starting to collapse?

Thank you.

The symptom I expected was that it might feel cold, damp or soft. But it's hard plasterboard and feels the same as the rest of the ceiling.

I can call a local builder tomorrow to check but worried they might be busy for Christmas. Although if it's a potential emergency we will need to get it sorted soon

It's 60s and probably redone 20 years ago. It's a smooth plasterboard, that's got plaster on it. The bit that's got the dip can be seen because of the spotlights on the ceiling causing a shadow.