Fixing celotex boards

[trevt]

Hi all

A bit of advice if I may, please....

I'm refurbishing a dormer bungalow, the plans (agreed with building control) require celotex between rafters and then under the rafters. Plasterboard will then be fixed over this.

The original front half of the roof will have 50mm boards between the rafters with a further 70mm board over the rafters at 90 degrees. My question is how to fix the over rafter insulation.

My first thought was to cross batten the rafters with 2x3 and fit the insulation between and then board. My second thought was to lay the full 8x4 sheet and cross batten with 2x1 over them - giving a void between insulation and plasterboard. Obviously I'll need some long nails/screws to go through the batten, insulation and into the rafters.

I'd prefer the second option as, whilst more difficult to man handle the sheets, I've less cutting and a void for cable etc.

Any reason I can't/shouldn't do it this way?

Thanks in advance

I'd

 

[noseall]

Why cross batten at all?

Just friction fit the 50mm celotex between rafters then screw celotex beneath then screw your plasterboards through the 70mm stuff straight into the rafters.

You will need some pretty looooong screws mind you.

 

[catlad]

You can get 125mm plasterboard screws.

 

[trevt]

Be honest hadn't thought of going direct....

main reason I was thinking of battening is because not all of the roof will be plasterboarded. There's a section in the eaves (about 2 m width) and above the room ceiling (flat over the centre and again 2m) that won't be directly plasterboarded but will have the celotex.

Given that and the fact the building control want to inspect post insulation but pre-plaster I need something to hold them up short-term.

Thanks