Stud ceiling to cover cracked lathe & plaster - what timber size?

29 Feb 2020
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United Kingdom
I live in an old terrace and in all the upstairs bedrooms the lathe and plaster ceilings are starting to crack.

I don't think i should overboard them as the lathe and plaster is hanging off small 3" x 1" timbers resting on the upstairs walls. If it's sagging now it's not going to help adding weight to it?

we have nice high ceilings so I'd like to look at building timer stud ceiling to them plaster board over and skim. I'd probably get some extra insulation in at the same time so the only load would be the insulation, plasterboard and plaster.

The middle room the shortest span is 2950

The bigger room the shortest span is 3885

Any advice on timber size and spacing?
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2950mm is approximately 10ft, 3885mm is approximately 13 feet. For floor joisting that would mean by rough rule of thumb I'd be looking to something like 5 x 2in C16 on 400mm centres for the smaller room with 6.5 x 2in C16 on 400mm for the bigger one. For ceilings you can happily go to 600mm centres, but without additional support from above I doubt that I'd go less than 4 x 2in C16 on the smaller room and 5.5 x 2in C16 in the larger room with a row of solid strutting across the middle to stiffen things up. TBH if you had some load bearing structure above such as a purlin that you could attach to this would be an easy job for metal framing (MF stud).

BTW if you go to C24 instead of C16 it should be possible to go down a wee bit in size.

C16 and C24 are structural gradings with a controlled level of knots and other defects as opposed to the rubbish "banana pine" white wood carcasing served up by B&Poo, etc
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You could use a larger timber thru centre of the short span to reduce timber size overall.

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