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insulating a flat roof

  • 20-12-2008 4:55pm
    #1
    magicbastarder
    Moderators, Category Moderators, Arts Moderators, Sports Moderators Posts: 50,895 CMod ✭✭✭✭


    i've a flat roof extension on the back of the house, about 20' x 11'.
    (one) problem is that there is no insulation in it - there's about 8 inches between the ceiling plasterboard and the planks of the roof itself, with about 10 inches between the joists.

    is there any way of getting insulation into these gaps without tearing the ceiling down? several ideas which have been bandied about include taking off the panel at the side, and sliding slabs of insulation in, or punching a few holes and injecting insulation. which is the most realistic?


Comments

  • #2
    RKQ
    Registered Users, Registered Users 2 Posts: 2,292 ✭✭✭RKQ


    I wouldn't consider foam.

    You could cut 60mm or 75mm thick xtratherm or kingspan foil insulation boards and try to friction fit them between joists - assuming they span the shortest length of 11'.

    It would be extremely difficult to do without removing the ceiling! But it might be possible to feed an 8' length in by removing the fascia.
    There will be struts, usually at 4' centres, between all joists. These struts will prevent you insulating between the joists!

    Bite the bullet and remove the ceiling, then install 100mm insulation board or 150mm fibre glass.
    Or install an insulation board with a slab bonded to it and skim the ceiling - this would take at least 65mm off the ceiling height - 2.4m is the recommended ceiling height.


  • #3
    magicbastarder
    Moderators, Category Moderators, Arts Moderators, Sports Moderators Posts: 50,895 CMod ✭✭✭✭magicbastarder


    cheers - figured that'd probably be the best way of doing a thorough job.


  • #4
    jdpl28
    Banned (with Prison Access) Posts: 186 ✭✭jdpl28


    one other way would be to insulate from above. you can get a roofer out to put insulating boards above the current felt, then put new felt above this. Theres a number of other different ways to do it, one doesn't require refelting above the insulation - google Styrodour.

    Looking into getting it done for a flat roof myself, so let me know how it goes :-)


  • #5
    magicbastarder
    Moderators, Category Moderators, Arts Moderators, Sports Moderators Posts: 50,895 CMod ✭✭✭✭magicbastarder


    RKQ wrote: »
    Bite the bullet and remove the ceiling, then install 100mm insulation board or 150mm fibre glass.
    Or install an insulation board with a slab bonded to it and skim the ceiling - this would take at least 65mm off the ceiling height - 2.4m is the recommended ceiling height.
    after lots of reading - including this thread - i'm a bit more educated about things - including the need for a vapour barrier, which is not currently there.
    i've no way of getting cross ventilation in; plus, where is the danger of condensation at the moment? is there not a danger as is without any vapour barrier or insulation already (i.e. if it's possible for condensation to build up, would it not already have occurred?)

    i'd preferably be going for what you suggested above, either fibreglass between joists and using foil lined plasterboard, or backed plasterboard; have to measure the ceiling height tomorrow.


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