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Anonymous
Anonymous asked in Home & GardenDo It Yourself (DIY) · 2 months ago

If I put loft boards downs, do I still need a double layer of insulation roll underneath?

I am worried that compressing the stuff might cause cracks in the ceiling etc

Update:

* There is already one layer of insulation down but was told in house survey it wasnt usually enough and needed two layers

Update 2:

Current depth of insulation in the UK is recommended at 300mm (11 inches)

Update 3:

Yup thanks guys, some good advice

7 Answers

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  • 2 months ago
    Favourite answer

    you are correct to worry ...loft boards are for light storage only..the joist below are not deep enough to carry weight ..and compressing insulation will  crack the ceiling ..in the uk insulation should be 275mm ..11" deep ..the insulation must NEVER cover the void between wallplate and soffit ..air must be allowed to circulate ....FYI  average floor joist depth 200mm ..8" average ceiling joist 100mm 4"   CAUTION!

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    • boy boy
      Lv 7
      2 months agoReport

      a soffit is the section between the outside wall and the fascia board ..its underneath ..a wallplate is a timber ..normally 4x3 ..or 4x2 .thats sits on the inside wall and carries the roof weight ...no roof weight is carried by the outside wall ..11"is 275mm ...12" is 300mm ..

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  • yep                

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  • 1 month ago

    fibreglass insulation should never be compressed the way it works is to catch warm air particles in the voids in the fibres. i,m not a fan of loft legs as it removes a lot of the head height in a loft , if this is not an issue then perhaps go ahead. An alternative idea is to insulate the pitch of the roof this can be done easily by a capable diy person using products such as multi foil insulation   these can be staple to the underside of the joists on the pitch of the roof and can be the equivalent of around 200mm of fibreglass. all joints need taping but doing it this way also helps keep the things you are storing in the loft safer and if you want to spend any time up there will keep it warm.

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  • Anonymous
    2 months ago

    The ceiling cracks BECAUSE the loft ceiling joists are not BIG ENOUGH to hold your weight.  The floor joists under me is 2"x12"@16"centers.   Chances are that your ceiling joists are 2"x8"@16"centers (where they SHOULD BE AT LEAST 2"X10"

    .The loft is not meant for carrying people weight.

    -there is no usable attic for you.  It can only hold insulation to insulate the box underneath.  Insulation has no weight.  Insulation needs to be fluffy(not compressed) for it to work its best and insulate the room below it.

    .  In my area houses were insulated with 8" of insulation.  Recently that has been upped to 24" on the ceiling...just to make the house more cozier.(Warmer in winter and cooler in summer)

    It is not a usable spot.(such as for storage) Stuff is heavy.

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  • 2 months ago

    my solution to that was to nail 2x2 [square 50 mm stock] directly to the ceiling joists before putting the added insulation in there and my boards atop that. Trapped and immobile air is what provides the insulation effect, compressed insulation is no better than a similar thickness of uncompressed insulation, so unless you do something like i did, the added insulation is useless and a waste of your money. [PS: there's no reason this can't be done twice to get sufficient added height]

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  • C
    Lv 7
    2 months ago

    Google "loft legs" or "loft risers."  These attach to the joist and support loft boards creating a cavity for increased insulation without compressing it.  You can get them at any major diy store or the usual online places.  Loft boards are not insulation in themselves.  Be careful to maintain airflow up there.

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    • Josh2 months agoReport

      Yeah, I don't think Im going to bother boarding it, reading all the horror stories about celings bowing under weight of boards + insulation

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  • Anonymous
    2 months ago

    The insulation should only fill the space from the ceiling sheetrock to the top of the rafters.

    The flooring boards go across the top of the Rafters, there should be no compression.

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