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U-value for attic

  • 12-05-2009 11:21AM
    #1
    HappyBetty
    Closed Accounts Posts: 5 ✭


    Hi All,

    i hope someone can help with this. I have an attic that is unheated with a pitched roof. If i insulate between the rafters with spray foam insulation will i get a better U-Value than inuslatin between the joists at ceiling level.
    Will the extra layer of air cause the u-value to decrease?

    Thanks :)


Comments

  • #2
    sydthebeat
    Subscribers, Paid Member Posts: 44,928 ✭✭✭✭sydthebeat


    HappyBetty wrote: »
    Hi All,

    i hope someone can help with this. I have an attic that is unheated with a pitched roof. If i insulate between the rafters with spray foam insulation will i get a better U-Value than inuslatin between the joists at ceiling level.
    Will the extra layer of air cause the u-value to decrease?

    Thanks :)

    spray foam has an insulating value similar to quilted material (0.04)... therefore you would need a similar thickness of this foam to get the same u value as quilted insulation.

    a minimum thickness of 300mm is currently recommended between and over joists... its highly unlikely you can get this thickness between your rafters, without doing substantial extra work to widen them out...


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