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roof insulation

  • 21-06-2006 10:49am
    #1
    jayo99
    Registered Users, Registered Users 2 Posts: 365 ✭✭


    ok ok.. I've read the other posts about it but still need to get an answer..

    I'm looking to insulate between the rafters on a new build.. already have some rolls of rockwool insulation (let over from a previous job).. 150mm... Rafters are 7x2 (well 6.75 inch... x 1.75 y'know yerself)..

    Question is .. Is there enough room for ventilation ? Or do I need to allow for more .. say ~ 2 inches ?

    Cheers
    Jayo


Comments

  • #2
    muffler
    Registered Users, Registered Users 2 Posts: 46,545 ✭✭✭✭muffler


    Bldg regs state that a clear space of 50mm to be retained between insulation and underside of felt. TBH if you had 30-40mm i dont think anyone would pull you on it


  • #3
    paulmallon
    Registered Users, Registered Users 2 Posts: 104 ✭✭paulmallon


    does it not depend on the type of felt you are using?
    theres a breatheable membrane which doesnt require an air gap.
    again im not 100 % sure:


  • #4
    Viking House
    Registered Users, Registered Users 2 Posts: 551 ✭✭✭Viking House


    You can put the insulation up against the breather membrane when you have a vapour barrier on the inside.
    The air gap is to allow insulation dry out when it gets wet from water vapour coming from inside the house from respiration and cooking etc,.
    Wet insulation doesn't work.


    If you cross batton with 25mm of rockwool on the inside you cut out the cold bridging through the rafters and the 25mm gives the effect of 75mm between the rafters.
    We use Softboard externally for this reason but also to give a windstopping effect.


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