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Wool insulation packed down

  • 30-03-2010 01:31PM
    #1
    Ferocious
    Registered Users, Registered Users 2 Posts: 43 ✭


    Is there any benefit to be gained from packing wool or fibre glass insulation into a space shallower than the thickness of the insulation, say 12 inch insulation packed down to 9 inches between joists?
    Do you end up with the effectiveness of 9 inches of insulation, just a bit more compacted?2
    I’ve got different information from different suppliers and fitters.


Comments

  • #2
    sydthebeat
    Subscribers Posts: 42,643 ✭✭✭✭sydthebeat


    Ferocious wrote: »
    Is there any benefit to be gained from packing wool or fibre glass insulation into a space shallower than the thickness of the insulation, say 12 inch insulation packed down to 9 inches between joists?
    Do you end up with the effectiveness of 9 inches of insulation, just a bit more compacted?2
    I’ve got different information from different suppliers and fitters.

    you pretty much end up with the effectiveness of 9" of insulation.

    the insulative agent is the trapped air... the more you pack a material the more air you force out...


  • #3
    gman2k
    Registered Users, Registered Users 2 Posts: 4,076 ✭✭✭gman2k


    sydthebeat wrote: »
    you pretty much end up with the effectiveness of 9" of insulation.
    I would disagree with this statement.

    The rule is don't compress glass fibre insulation, as you are greatly reducing the trapped air capacity of the material - which is the part of the material that is actually working as an insulant.
    9" of uncompressed glass fibre insulation will have more air contained within it's depth than 12" compressed to 9".
    9" of uncompressed insulation will have better insulation properties than 12" compressed down to 9".


  • #4
    sydthebeat
    Subscribers Posts: 42,643 ✭✭✭✭sydthebeat


    gman2k wrote: »
    9" of uncompressed insulation will have better insulation properties than 12" compressed down to 9".

    i will agree with this contention..... ;):D


  • #5
    Ferocious
    Registered Users, Registered Users 2 Posts: 43 ✭Ferocious


    Thanks guys. I was thinking as much. The supplier packing in 12" must be just trying to sell more stuff.
    Another question - are there only certain types of 'breathable felt' that allow you to put insulation right up to it. Most installers are recommending an air gap but the same guy that wants to pack between the joists wants to fill up to the membrane between the rafters also.


  • #6
    Mellor
    Registered Users, Registered Users 2 Posts: 40,259 ✭✭✭✭Mellor


    gman2k wrote: »
    I would disagree with this statement.

    The rule is don't compress glass fibre insulation, as you are greatly reducing the trapped air capacity of the material - which is the part of the material that is actually working as an insulant.
    9" of uncompressed glass fibre insulation will have more air contained within it's depth than 12" compressed to 9".
    9" of uncompressed insulation will have better insulation properties than 12" compressed down to 9".
    I'd agree with this.
    Ferocious wrote: »
    Thanks guys. I was thinking as much. The supplier packing in 12" must be just trying to sell more stuff.
    Another question - are there only certain types of 'breathable felt' that allow you to put insulation right up to it. Most installers are recommending an air gap but the same guy that wants to pack between the joists wants to fill up to the membrane between the rafters also.
    And only certain felts are breathable. If it is a regular felt, then maintain 50mmm gap


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