I am about to look at plasterboarding my ceiling in my new dining room.

The dining room is created by halving the size of the garage, and the flat roof joist are original to the garage.

The ceiling was originally boarded with aspestalux or what ever you call it, but will obviously now be plasterboarded and skimmed.

The only niggle I have is that the joists are not 100% level.  If I place a staright edge on the ceiling there is some 10-15mm difference in a couple of the joists.  This obviously did not matter too much when nit was a garage.

I not really want to have to cross batten to correct this, and wonder how much of a problem it would be if I simply boarded, and let the plasterboard take up the difference?

Would this cause huge issues for the plasterer, and would this be noticeable?

Just had a plasterer round to look at a similar problem on a new build!!. upto 5mm tolerence on mine and he says i can get away with using 15mm board but any more than 5mm out and it will need counter battens!! Good luck!!

Looking closer, it only looks like two joists are out, and these are higher than they should be.

I may add two additional joists bolted next to these high ones.

Roll on the weekend, and working at home