Combining foil quilt and rockwool for joist insulation

Discussion in 'Floors, Stairs and Lofts' started by london_diy, 12 Dec 2021.

  1. london_diy

    london_diy

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    Hi all

    I'm having the insulation in my loft removed and redone (due to mice) and as I wan't to keep the boards on the joits (and keep a cold loft) have been offered the option to have 5cm rockwool pushed up against the ceiling plasterboard, plus a foil quilt (e.g. the YBS superquilt) draped under the boards.

    My concern is that if they seal the quilt around the edges (which I understand is what is required) there is a risk of condensation between the rockwool and the quilt.

    Does anyone have experience of this type of configuration? Did it cause problems with condensation?

    Total depth of the joists is 9.5cm. I'm not looking to get to 100% requirements of buildings regs, just to achieve maximum heat retention possible via resonably priced under-the-boards methods.

    Thanks!


    Londoner
     
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  3. RandomGrinch

    RandomGrinch

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    Hi,

    I'm only a DIY'er, so feel free to ignore and I may be wrong! :)

    However, at a recommended loft insulation thickness of around 250 - 270mm (for Rockwool), your proposed solution isn't going to get anywhere close!

    There is also some debate on here and elsewhere about the efficacy of superquilt insulation. If it's done properly it may work. Decent air gaps are required around it to create insulating air pockets; if it is squeezed between a layer of Rockwall and the loft boarding, these air pockets may be lost.

    The quilting is also expensive.

    Personally, in my loft, I have laid Rockwool between the joists and another layer perpendicular over the top (ensuring soffit ventilation is maintained! ;) ). I have then used a loft leg system to raise the loft boards above the insulation.

    Good luck! :)
     
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