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Deleted member 23452
Guest
WRONG MR BUILDER.
A 12.5 board weighs 20kg and covers 2.9m2 approx. Your average upstairs bedroom would be 15m2 so you would be adding approx 100kg weight, spread across a 15m2 ceiling, 10 kg per m2. That won't make your joists bend lol.
If it were a downstairs ceiling how would it stand up to me, a 100kg person walking on the upstairs floor daily ?
9.5mm board even lighter, easier for the poor plasterer eg nisus
Stick the kettle on and a bit of cash would be handy guvnor
I'd stick to buttering walls if I were you. Even if you ignore the additional weight of the skim etc and say you figures are correct, you seem to be missing the fact that it's overall weight on a 100mm bearing at each end which causes the joists to sag.
Giving a weight per square metre is a loading for a solid surface. For a beam it's point loading and overall weight.
You even manage to point out the flaw in your own argument. A ground floor ceiling is fixed to the floor joists for the first floor. Guess what? Those joists are sized to carry that load. What load do you imagine the joists below a loft as sized to carry?
You do seem to excel at talking bollox while you try and make yourself sound clever.