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  • FIRST POST
    • skidbum1
    • By skidbum1 20th Oct 19, 11:20 PM
    • 2Posts
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    skidbum1
    Can Joist Insulation be used in Rafters?
    • #1
    • 20th Oct 19, 11:20 PM
    Can Joist Insulation be used in Rafters? 20th Oct 19 at 11:20 PM
    Hello, I am putting loft panels down and as a result a lot of the insulation (put down new in 2007) is becoming redundant (a small bit is still under the panels). Has anyone come up with a method of using it the rafters? It is still in good condition. If not what is the most cost effective and easiest method of insulating my roof to compensate for the loss of joist insulation?
Page 1
    • FreeBear
    • By FreeBear 20th Oct 19, 11:54 PM
    • 3,222 Posts
    • 4,179 Thanks
    FreeBear
    • #2
    • 20th Oct 19, 11:54 PM
    • #2
    • 20th Oct 19, 11:54 PM
    The conventional way of boarding over thick insulation is to use stilts to support the boards. e.g. https://www.screwfix.com/p/diall-loft-storage-stilts-210mm-12-pack/243gf
    Other lengths and sizes to suit larger joists are available.
    Her courage will change the world.

    Treasure the moments that you have. Savour them for as long as you can for they will never come back again.
    • skidbum1
    • By skidbum1 21st Oct 19, 12:35 AM
    • 2 Posts
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    skidbum1
    • #3
    • 21st Oct 19, 12:35 AM
    • #3
    • 21st Oct 19, 12:35 AM
    I have already gone down the non-stilts approach!
    • Doozergirl
    • By Doozergirl 21st Oct 19, 6:35 AM
    • 27,837 Posts
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    Doozergirl
    • #4
    • 21st Oct 19, 6:35 AM
    • #4
    • 21st Oct 19, 6:35 AM
    Then you'll need solid insulation cut between your rafters as the rafters are never going to hold 30cm of rockwool and it will slump over time anyway, I would suspect, if you try and suspend it.

    Solid insulation is thinner than you'd need to Achieve the same uValues with rockwool. Not cheap, but at least it will pay you back relatively quickly in savings. The stilts were probably the easiest way, tbh.
    Everything that is supposed to be in heaven is already here on earth.
    • ANDY597
    • By ANDY597 21st Oct 19, 8:23 AM
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    ANDY597
    • #5
    • 21st Oct 19, 8:23 AM
    • #5
    • 21st Oct 19, 8:23 AM
    I would follow doozers advice and cut solid insulation between the rafters ensuring a tight fit, but don't forget the air gap between outside and the insulation.

    In answer to your question though if you were adamant you wanted to, then you would leave an air gap then the rockwool, then suspend it in there with a breathable membrane to stop it from sagging out. How efficient it would be in there would be debatable.

    From your question though it struck me. What size are there joists if most of the insulation is going? Joists may not be suitable to support a floor.

    Possible solution is to increase the joist height to accommodate more insulation underneath. Hanging new joists alongside existing is within a diyers capability thanks to modern joists hangers.

    Hope this helps.

    • Davesnave
    • By Davesnave 21st Oct 19, 9:02 AM
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    Davesnave
    • #6
    • 21st Oct 19, 9:02 AM
    • #6
    • 21st Oct 19, 9:02 AM
    We get a good bit of air whistling through our loft and I suspect this has some bearing on our lack of condensation issues. Frankly, I wouldn't think insulating our rafters would do a lot to keep us warm, unless we also restricted air flow.

    I wouldn't be doing that.

    I've used solid insulation down the central aisle in our loft, where there's a boarded walkway. Everywhere else, it's about 300mm of fluffy stuff. Because I still want to store Christmas decorations, baby chair, buggy, and other rarely-used, light paraphernalia, I've designed platforms to fit in the 'W' of the roof trusses that may be reached from the walkway. Works OK.
    Things are more like they are right now than they've ever been.




    • TELLIT01
    • By TELLIT01 21st Oct 19, 9:07 AM
    • 7,222 Posts
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    TELLIT01
    • #7
    • 21st Oct 19, 9:07 AM
    • #7
    • 21st Oct 19, 9:07 AM
    If you do want to reuse the current insulation, you could try using plywood as a backing, fixed over the rafters. It will definitely be a two person job.
    • Doozergirl
    • By Doozergirl 21st Oct 19, 10:35 AM
    • 27,837 Posts
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    Doozergirl
    • #8
    • 21st Oct 19, 10:35 AM
    • #8
    • 21st Oct 19, 10:35 AM
    If you do want to reuse the current insulation, you could try using plywood as a backing, fixed over the rafters. It will definitely be a two person job.
    Originally posted by TELLIT01
    There won't be any airflow?
    Everything that is supposed to be in heaven is already here on earth.
    • ANDY597
    • By ANDY597 21st Oct 19, 6:17 PM
    • 403 Posts
    • 291 Thanks
    ANDY597
    • #9
    • 21st Oct 19, 6:17 PM
    • #9
    • 21st Oct 19, 6:17 PM
    Dooze, that might work as long as there's an air gap between the insulation and rafters.

    I think what they meant was

    Airflow gap

    Recyled insulation

    Board to face it off and stop it falling down like plasterboarding a wall.

    Sounds like a lot of effort when solid insulation is available to make life easier.

    OP check out seconds and Co for slightly damaged Kingspan at a fraction of the cost. Buyer beware board won't be perfect. May have a chunk etc missing or an odd shape etc

    • Doozergirl
    • By Doozergirl 21st Oct 19, 7:24 PM
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    Doozergirl
    Okay, but I'm not convinced that one can maintain a consistent air gap with fluffy insulation, especially if it's 2nd hand, and then if you screw boards on it, they have to be able to screw to something and then you don't know if you've bridged the air gap with the pressure of the thing holding it on.

    It's just a bad idea all round.
    Everything that is supposed to be in heaven is already here on earth.
    • Tom99
    • By Tom99 21st Oct 19, 7:35 PM
    • 5,063 Posts
    • 3,561 Thanks
    Tom99
    Okay, but I'm not convinced that one can maintain a consistent air gap with fluffy insulation, especially if it's 2nd hand, and then if you screw boards on it, they have to be able to screw to something and then you don't know if you've bridged the air gap with the pressure of the thing holding it on.

    It's just a bad idea all round.
    Originally posted by Doozergirl
    And if there is an air gap to start with then the insulation is likely to slump towards the bottom.
    • FreeBear
    • By FreeBear 21st Oct 19, 11:35 PM
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    • 4,179 Thanks
    FreeBear
    Would be a lot cheaper and much less hassle to just go and get a few bags of stilts. Unless the space is being boarded out as a loft conversion, there really isn't anything to be gained from filling the gaps between rafters with insulation. If the loft is being converted in to a habitable space, then it needs to be done properly rather than trying to save a few pounds on reusing old insulation.
    Her courage will change the world.

    Treasure the moments that you have. Savour them for as long as you can for they will never come back again.
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