Advice on fixing celotex beneath rafters

Discussion in 'Builders' Talk' started by Willy Duwitt, Sep 29, 2009.

  1. Willy Duwitt

    Willy Duwitt New Member

    Hi

    I'm looking to fix some Celotex boards to the underside of the rafters in our loft conversion to avoid cold bridging. I'll be fixing the boards at 90 degrees to the rafters but my question is what do I use to fix them? long drywall screws or nails and at what spacings?

    I'll be laying 12.5mm p/board over this. Do I now fix this parallel to the rafters or in line with the insulation and, again, what do I use to fix it??

    Any advice would be appreciated.

    Thanks
  2. timber ninja

    timber ninja Member

    how thick is the celotex/kingspan your using? . . .
  3. Willy Duwitt

    Willy Duwitt New Member

    Celotex will probably be 30mm
  4. trench

    trench New Member

    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
  5. timber ninja

    timber ninja Member

    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
  6. Willy Duwitt

    Willy Duwitt New Member

    Thanks Trench. I am aware of those and it's precisely because they're £££'s more that I've opted for the bog standard, cheaper option. Now, if only I could get someone to advise me on how to fix the damn things.

    :)

    Cheers
  7. Willy Duwitt

    Willy Duwitt New Member

    Many thanks for that Mr Ninja. That's exactly what I needed to know.

    Much appeciated.
  8. timber ninja

    timber ninja Member

    Cor . . . mr ninja, i like that.

    no worries . . .
  9. building control

    building control New Member

    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.
  10. Willy Duwitt

    Willy Duwitt New Member

    Thanks for the additional info, BC.

    Just out of interest, what length screws would you guys recommend with 30mm Celotex and 12.5mm p/board? At a total thickness of 42.5mm, would a 65mm screw be long enough or would I need to use 75mm?

    Cheers
  11. timber ninja

    timber ninja Member

    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
  12. imran_

    imran_ New Member

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

    Willy Duwitt New Member

    Regs......????

    Yes, it does. What's your point?
  14. building control

    building control New Member

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

    timber ninja Member

    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?
  16. Willy Duwitt

    Willy Duwitt New Member

    Ok. Maybe I should clarify.

    Yes, I have 120mm insulation between the rafters but as my question was simply about attaching the stuff to the underside I didn't feel it was necessary to bore everyone with any other details.

    Anyway, many thanks to the guys who replied with constructive comments. It really is much appreciated.

    Cheers
  17. dryliner essex

    dryliner essex New Member

    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.

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