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Flat roof insulation options

  • 17-12-2011 1:21pm
    #1
    dwiseman
    Closed Accounts Posts: 138 ✭✭


    Hi Im just looking for opinions and advice for insulation options for a flat roof if anyone can point me in the right direction.

    Im currently putting a flat roof extension of 450sq ft onto the back of our house. We will soon be approaching roof level and I was just wondering what the best insulation option for the roof might be. There will be an 8ft X 4ft apex rooflight window with low e safety glass running through the centre of the roof. The roof will be rafters, with a liquid plastic coating.

    So basically just wondering should there be insulation above the rafters? I was thinking of insulating between the joists and then using a 50 or 90mm insulated slab on the ceiling, but not sure if that would suffice? Im not looking to make it suffice, I do want it to be well insulated but I dont want to break the bank either, if you'll pardon the pun!! Any advice would be greatly appreciated.


Comments

  • #2
    Carlow52
    Closed Accounts Posts: 2,389 ✭✭✭Carlow52


    1: what depth the roof rafters?
    2: whats the max depth of insulation u can add having regard to tying in with existing etc
    3: whats the plan for ventilation of the roof, dealing with air-tightness/vapour membrane etc since u a re putting a liquid plastic on the top


    90 mm is nothing these days for a flat roof: Id be looking at 300-400.

    will send u a pm with a link for some ideas


  • #3
    BryanF
    Moderators, Home & Garden Moderators Posts: 10,146 Mod ✭✭✭✭BryanF


    plasterboard, VB sealed and taped, 150mm rockwool between joists (presuming 6' joist), 17mm osb3 sheet, 200mm PIR or phenolic, separating layer and your preferred waterproof finish.


  • #4
    dwiseman
    Closed Accounts Posts: 138 ✭✭dwiseman


    Thanks for the replies guy, they have really helped as I now have an idea of what my options are. cheers :)


  • #5
    broke
    Registered Users, Registered Users 2 Posts: 26 ✭broke


    There is a new flatroof system out now using a Firestone EPDM rubber sheet. It has a 50 year life span and you put the insulation on top of the roof. I got it on mine and it worked great. There is a demo vid on flatroof.ie


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