How to fix this ceiling?

[RF Lighting]

My parents had a two storey extension built about 30 years ago.

The ceiling in the ground floor room has cracked quite badly on what appears to be the joints between the plasterboards.

What's the best way to repair this? Will it be ok to screw the boards back to the joists at 150mm centres, scrim the joints and reskim the ceiling, or does it need to be dropped, reboarded and skimmed? I don't know if the original ceiling was scrimmed on the joints when it was installed, and wether they used 9.5mm or 12.5mm boards.

I'd ideally like to avoid this as it will require the replacement of the coving too.

Here's a couple of photos of the affected ceiling.

Untitled

• RF Lighting
• 29 Dec 2014
• 1

Untitled

• RF Lighting
• 29 Dec 2014
• 1

 

[roughcaster]

Screw it back up all over as you said RF. Make sure you know where the ceiling joists and any noggins are first, and also think about any cables/pipes that might be in the ceiling. Check to see if there are any tapes on the split joints and if there are, rip them all off. I'd check every joint, both along the board joints and across the joints.
Nowadays, the vast majority of ceilings are boarded with 12.5mm plasterboard, but in the past, they used mostly 9mm boards. Because the boards then were thinner, many sagged over time, because of the downward weight, plus the span between each joist didn't help with thinner boards.
Anyway RF, spend good bit of time screwing/tightening up, all over the boards, checking over the joints in the boards and removing any old tapes/old joint cement etc, then you can think about getting a plasterer in to give you a quote to prep, re-tape and then skim your ceiling, without any worry about damage to the coving. Good luck to you anyway.