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Insulating roof rafter of less than 100mm

  • 06-01-2013 9:28pm
    #1
    Ush1
    Registered Users, Registered Users 2 Posts: 11,488 ✭✭✭✭


    I have a ventilated roof and want to insulate it with rigid material(kingspan or xtratherm). The problem is my rafters are only 95mm depth. Leaving a 50mm gap for ventilation that only leaves 45mm for insulation. Any tips on what I could do? Does rigid come in that thickess or is there any way to add depth?


Comments

  • #2
    BryanF
    Moderators, Home & Garden Moderators Posts: 10,146 Mod ✭✭✭✭BryanF


    Ush1 wrote: »
    I have a ventilated roof and want to insulate it with rigid material(kingspan or xtratherm). The problem is my rafters are only 95mm depth. Leaving a 50mm gap for ventilation that only leaves 45mm for insulation. Any tips on what I could do? Does rigid come in that thickess or is there any way to add depth?
    Place additional insulation below the rafters?


  • #3
    Ush1
    Registered Users, Registered Users 2 Posts: 11,488 ✭✭✭✭Ush1


    BryanF wrote: »
    Place additional insulation below the rafters?

    Yeah I'll be doing that but how thick would I need to go to be up to regs do you reckon?


  • #4
    A fella called fish
    Banned (with Prison Access) Posts: 188 ✭✭A fella called fish


    If the insulation has to be installed as high as possible then fix battens along the length of each rafter to effectively make the rafters appear deeper. You can the. Install the insulation between the rafters as required.

    Alternatively fix insulation to the underside of the rafters if headroom is not an issue?

    Or - cut the insulation sheets to 45mm. Not ideal but every little helps!


  • #5
    BryanF
    Moderators, Home & Garden Moderators Posts: 10,146 Mod ✭✭✭✭BryanF


    Ush1 wrote: »

    Yeah I'll be doing that but how thick would I need to go to be up to regs do you reckon?
    See the current part L


  • #6
    Ush1
    Registered Users, Registered Users 2 Posts: 11,488 ✭✭✭✭Ush1


    Cheers for that lads. Also, what would be the best way to get cabling in without compromising the thermal envelope. The room would need a power socket, cable for satellite and also for an aerial.

    Would I have to puncture the rigid insulation at some point, run the cables through and then seal around the hole?

    EDIT: Just spoke to Kingspan who were very helpful.

    They said 50mm K7 should be fine and then 72.5mm K18 under the rafters would bring it up to refurb regulations.

    For wiring they said rather than insulating the stud walls I could insulate the rafters all the way to the eaves and just have 60mm K7 on the underside there in the sides rather than the K18.

    Probably no point in insulating the ceiling joists if I'm insulating the rafters all the way to the eaves?


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