False ceiling build and insulated.

Good Evening,

I am in the middle of a bedroom referb and after moving the horrendously looking (and dangerous) polystyrene tiles I'm left with a roof which is not pleasing to the eye. I will post a pic below as I have one on my phone. There is also a beam running through the bedroom so I can hide that by dropping the ceiling too. The roof above the existing ceiling is a flat one which we have just had replaced with GRP.

Anyway I'm going to build a false ceiling. The plan is to build a wooden frame with strengtheners, use 50mm celotex/kingspan for insulation then 12.5mm plasterboard. There will be about a 100mm air gap between the insulation and existing ceiling. Do I need to worry about condensation. Also I was going to use 3 x 2" CLS for the stud work unless anyone has used anything better. The area is around 9 square metres.

Any information would be great.

Many thanks in advance.

And how is the ceiling void going to breath through a layer of glass fibre? are there enough soffit vents (any?). Use at least 100mm of foam and a VCL below it.
Frank

theprinceofdarkness said:

And how is the ceiling void going to breath through a layer of glass fibre? are there enough soffit vents (any?). Use at least 100mm of foam and a VCL below it.
Frank

Click to expand...

New tactic. I'm using xtratherm as insulation.

How do I prevent condensation in the void? Surely 2 layers of foil on the insulation and the insulation which is to prevent warm air loss will prevent warm air reaching the old ceiling??

I have just had all the materials delivere. The frame will be CLS 3x2, I have 50mm Xtrathrm for insulation and 12.5 plaster board ready to go. Just waiting for a condensation solver and I'm away!

I can get a roll of vapour barrier from SCREWFIX which is local to me should I need it.

Thanks

Soffit vents? Foam and its silver paper is in theory vapour proof, unfortunately the joints are not and the foam might (will?) contract over the years. Look at their specs on the manufacturers sites, often quoted as less then 1%, or an inch for a 9' run. Air is very slippery and will find its way through the smallest of holes.
Frank

My plan was to build the timber frame such that the plaster board goes flush straight across that against unsightly beam across the Middle of the bedroom. Would recommend and air gap here as well?