Ceiling joists - graded or not?

[Mog]

Hi - just had to take a loft ceiling out (long story as to why) and it was 3x2 joists. I'm going to put it back in with 4x2 - does the 4x2 need to be graded (to c16) or can it be ungraded? It'll be supported from a pitched roof with 4x2 rafters, span from front rafter to rear ~ 3.5m, plasterboarded, and will be used for some storage.

Thanks in advance. Matt

 

[Static]

Urm 4x2 C16s at 400 centres will span 1.93m maximum
Grade C24 will do 2.12m max.

You've removed the existing joists?? If they were 3x2's they sound more like part of a truss rafter and in that case shouldnt be removed without serious temporary support.

Can you post some photos?