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Hi.

I am putting a new independant ceiling below the existing ceiling in my living room. I live in a ground floor flat. The span is 3.8m across the room. I want to put the joists at 400 c/c. There will be no load from above as its indepandant. I am going to fix 2 sheets of plasterboard (12.5mm and 19mm) to the underside of the new joists and then skim.

Can anyone help with the sixe these joists should be?

Thanks

are they fixed to the ceiling above or suspended?
why 32mm of plasterboard. if for soundproofing dB chech and high density insulation?

HI, if there is no weight on the new joists then 6 x 2 should be ample, u could prob get away with even smaller timbers, id dry line screw the 12mm plaster board to the joints...joints should idealy be inbetween 400--600 centres! and then skim over

Is it just a case of lowering the ceiling?

There are tens of thousands of homes with twelve foot wide rooms where the traditional 4 x 2 inch joists have been in place as ceilings/floors for lofts, for over a hundred years, many are loaded with many things. You can add to this the weight of people walking across the lofts as well.

I would suggest a 4x2 be more than sufficient ensuring the joists are fixed mid span from the existing ceiling/flooring joists of the flat above. This fixing could be in the form of a hanger that enables the the ceiling to be much lower then 4 inches,the depth of the the new joists.
If the ceiling is completely independant obviously always span the shortest distance and consider a 6x2 but ensure the wall plate timbers (boundary ) are resin bolted to the masonary as the net weight of the ceiling as a whole with plasterboard and skim is cosiderable.

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