Advice on fixing celotex beneath rafters

how thick is the celotex/kingspan your using? . . .

 

kingspan do an insulation board with a plasterboard facing attached (TW56?) see if celotex do a similar product.
It may be more £££ but certainly quicker to fit

 

just drywalls for the combined insulation/plaster board, long uns . .

for insulation 1st just nail it on, as many fixings as you need to keep it stable. then fix the plaster board with drywalls straight through to the rafters. nice tight sandwich effect.

as for direction of plaster board i always try to leave the minimum 'free' edges. so im guessing parallel to rafters on your situation

 

Cor . . . mr ninja, i like that.

no worries . . .

 

Use two or three screws per board, then screw the plasterboards through both layers,

you are only holding the celotec there until you fix it permanently with the plasterboard,

the direction of the celotex wont matter just run them end to end, then mark the rafters for the plasterboard.

 

i would use the 75mm . . . mind you i like fixing things so they stay fixed FOREVER.

mind you,if it was friday, getting on for 4pm and all i had in the pouch was 65mm . . . i wouldnt loose sleep over it.

how much use am i? lol

 

"loft conversion...." - does 30mm meet Building Regs......????

 

I was assuming there will be 100mm between the rafters as well.

 

im using my amazing powers of deduction to guess you have insulation . . .between the rafters!
hence the term 'avoiding cold bridging'

c'mon imran give the guy some credit, nobody would just tack 30mm to the rafters and think its done . . . .

would they?

 

we generally get some off-cuts of p/board about 3 inch sq.
screw them to the cellotex into the rafters.this will hold it in place and then when your sheet of p/board is up just take the packer down.

 

Have you seen the insulation board retaining clip for fixing ceilings?

 

Speaking from experience (bitter experience that is), I would definitely include a vapour barrier before the plasterboard. Failure to do so risks condensation build-up and possible drips down onto the plasterboard, causing havoc with the paint.
Some like to fit the vapour barrier directly onto the rafters, i.e. with the 30mm insulation on the underside of the vapour barrier, but I prefer to get the 30mm insulation on first and then cover that with a complete sealed vapour barrier, and then add the plasterboard afterwards.
I use just a couple of screws with load spreading washers to help pull the 30mm layer of insulation tight up against the rafters. Once they're firmly held in place, I use a good stick like adhesive to stick the vapour barrier to the underside of the insulation, and then add the plasterboard ... again using load spreading washers on each screw. When I haven't used the load spreading washers, I've found that sometimes things work themselves loose or tight over time and the odd screw head with plaster on it pushes its way out creating a dimple in the skimmed plasterboard. Not much fun having to repair that after all the painting has been done and the room is furnished.

 

I'd use insulated plasterboard. Only one set of fixings needed quicker, plasterboard screws.