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Attic conversion-which insulation on rafters

  • 04-11-2014 8:47pm
    #1
    cally_lilly
    Registered Users, Registered Users 2 Posts: 3 ✭


    Hi. Doing attic conversion & head is absolutely mydered between all types of insulation.

    We initially thought spray form but our rafters aren't deep enough so they need to add more space to rafters which reduces headroom so that's out..

    There is super foil which u just staple onto rafters & its layers of tinfoil like & then plasterboard on top of it.

    Or there is the insulation boards u cut & slot I between rafters... Lots of work cutting

    Has anyone any experience wit either or which is best insulation to use


Comments

  • #2
    kieran.
    Registered Users, Registered Users 2 Posts: 1,175 ✭✭✭kieran.


    Forthe superfoil insulation to work you need a air gap between it and plasterboard. If space is an issue i'd go depth of the rafters minus nominal air gap in phenolic insulation and 37.5m phenolic drylning board to cut out the cold bridging.

    If price isnt an issue check out 'Aerogel' insulation which is nearly twice as effective as phenolic.


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


    >Spray foam has typically got a w/mk in the .03's so your looking at 200mm depth really to get under .2w/m2k (u-value)
    >The tinfoil is just that tin foil and not for use unless combined with other insulation
    >PIR boards fitted between the rafters might save the most space (.02's w/MK) but you should really have something under the rafters to reduce thermal bridge. So if you got 100 between and 50mm below min imo

    What is the depth of your rafter?
    Is it standar felt?
    Is the vent gaps at the eaves?
    Do you plan on installing vent gaps at the ridge/or vent tiles
    What is the width of the ceiling when measured at 2.4m over floor level?
    What is the width when measured at 1.2m over floor level?
    What is the type of cut roof?
    What supporting timbers are being altered what is your engineer specified for structural stability?
    Are you familiar with this: http://www.environ.ie/en/DevelopmentHousing/BuildingStandards/PublicationsDocuments/FileDownLoad,1657,en.pdf


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