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    • Zither
    • By Zither 3rd Jan 18, 7:37 PM
    • 330Posts
    • 41Thanks
    Zither
    Loft insulation
    • #1
    • 3rd Jan 18, 7:37 PM
    Loft insulation 3rd Jan 18 at 7:37 PM
    Hi All,

    OK so I appreciate that this sort of question has probably been asked at least 100 times but I have some specific questions that I'd like to understand so if anyone could help then that would be grand. I also appreciate a couple of these are a bit silly!

    My house is pretty cold so I'm investigating if I should refresh the loft insulation. Wickes have it on 3 for 2 rolls at the moment so I'm wondering if I should bite the bullet and just go buy some.

    1) My loft currently has 120-ish mm yellow wool-looking insulation (I couldn't say specifically what type it is). Not sure how old this is but it does look pretty old (from the dust on it like maybe 10-20 years). Does loft insulation degrade over time?

    2) If I bought any more, should I look to top up the old wool with new wool or get rid of the old wool and buy thicker?

    3) I appreciate that 120 mm loft insulation is an old standard. Would I really notice THAT much difference going from 120mm > 170mm > higher thickness?

    4) My loft is boarded out (by previous owner). There is only about 130 mm space under the loft boards (presumably why the loft has 120 mm insulation). I KNOW that in principle loft insulation should not be compressed into a smaller space because it's the air gap that keeps in the warmth. However, in practice, have any of you done this? Would a bit of compressed insulation be warmer than thinner uncompressed insulation? (I would ensure that the air gaps in the loft weren't covered).

    5) This is a bit random because I'm quite busy at the moment but... if I do buy the insulation and until I have time to install it - would it still be worth just laying it out on top of the loftboards? Or would this have zero effect?

    Any perspective on any of the above would be great thanks. I did read a couple of articles online about these but would prefer people's experiences

    Thanks

    Zither
Page 1
    • exiled_red
    • By exiled_red 3rd Jan 18, 8:07 PM
    • 232 Posts
    • 156 Thanks
    exiled_red
    • #2
    • 3rd Jan 18, 8:07 PM
    • #2
    • 3rd Jan 18, 8:07 PM
    If you are buying more roll type insulation I would just put it on top of the existing roll, however if your loft is boarded you won't simply be able to put it directly on top of the existing stuff. As you suggest you could put it on top of the boards but you would lose the ability to use the loft for storage or anything. If that doesn't bother you then I guess that is the easiest thing to do.


    If you want to use the loft for storage I imagine you would have to lift and re-lay the boards either on loft legs above the roll insulation or instead put some board type insulation under the current boards.
    • oz0707
    • By oz0707 3rd Jan 18, 8:18 PM
    • 536 Posts
    • 146 Thanks
    oz0707
    • #3
    • 3rd Jan 18, 8:18 PM
    • #3
    • 3rd Jan 18, 8:18 PM
    Think it's one of the quickest areas to see payback as the insulation is so cheap and can be diy'd. Double it up to around 300mm. Don't block ventilation near the eaves. Lift your lift boards up with some stilts screwed to trusses, cls ontop of stilts then boards ontop of this.
    • Zither
    • By Zither 3rd Jan 18, 9:27 PM
    • 330 Posts
    • 41 Thanks
    Zither
    • #4
    • 3rd Jan 18, 9:27 PM
    • #4
    • 3rd Jan 18, 9:27 PM
    Thanks exiled, oz0707,

    Is it hard to install legs/stilts/trusses? I was kind of hoping I could just unscrew the existing boards and pack the new insulation under it? Is this really a bad thing to do? I'm more interested in the 80% improvement I could gain rather than the 20% I might not gain from packing it too tight.

    All that said - will it definitely make an improvement moving from 110 mm to 200+ mm insulation? Would I notice it in the house?

    Thanks
    • oz0707
    • By oz0707 3rd Jan 18, 10:26 PM
    • 536 Posts
    • 146 Thanks
    oz0707
    • #5
    • 3rd Jan 18, 10:26 PM
    • #5
    • 3rd Jan 18, 10:26 PM
    Draughts will be next on your hit list after upgrading loft insu. I don't know what your houses standing losses are but think these are generally first two areas to tackle. Stilts easy but if boarded area not a great% of loft then perhaps leave that space.
    • Zither
    • By Zither 3rd Jan 18, 10:39 PM
    • 330 Posts
    • 41 Thanks
    Zither
    • #6
    • 3rd Jan 18, 10:39 PM
    • #6
    • 3rd Jan 18, 10:39 PM
    Draughts will be next on your hit list after upgrading loft insu. I don't know what your houses standing losses are but think these are generally first two areas to tackle. Stilts easy but if boarded area not a great% of loft then perhaps leave that space.
    Originally posted by oz0707
    Thanks yes. The house isnít particularly draughty - eg curtains donít move next to windows etc... it just doesnít seem to heat up/retain heat that well. So looking at whether to improve the loft insulation to help keep it a Bit warmer in winter
    • missile
    • By missile 3rd Jan 18, 10:39 PM
    • 9,378 Posts
    • 4,651 Thanks
    missile
    • #7
    • 3rd Jan 18, 10:39 PM
    • #7
    • 3rd Jan 18, 10:39 PM
    I wonder what the insulation value is for those loft boards?
    Perhaps it is as good as Xcm of insulation?
    "A nation's greatness is measured by how it treats its weakest members." ~ Mahatma Gandhi
    Ride hard or stay home
    • Zither
    • By Zither 3rd Jan 18, 10:46 PM
    • 330 Posts
    • 41 Thanks
    Zither
    • #8
    • 3rd Jan 18, 10:46 PM
    • #8
    • 3rd Jan 18, 10:46 PM
    I wonder what the insulation value is for those loft boards?
    Perhaps it is as good as Xcm of insulation?
    Originally posted by missile
    I also wondered this. I presumed tho it would be like wearing a thin raincoat on an icy day - works a little bit but is just the wrong choice of coat for the weather?
    • silverwhistle
    • By silverwhistle 4th Jan 18, 12:11 AM
    • 1,779 Posts
    • 2,349 Thanks
    silverwhistle
    • #9
    • 4th Jan 18, 12:11 AM
    • #9
    • 4th Jan 18, 12:11 AM
    I upgraded my loft insulation, and where I wanted to retain storage I put celotex (Kingspan?) down on top of the existing loft boards and then more loft boards on top of that. The rest I just added normal rolls on top. Easy DIY (I did it!) even if a bit fiddly cutting the insulation board to get into the loft and a littl expensive, but look out for offers. Very effective though
    • Zither
    • By Zither 4th Jan 18, 6:09 AM
    • 330 Posts
    • 41 Thanks
    Zither
    I upgraded my loft insulation, and where I wanted to retain storage I put celotex (Kingspan?) down on top of the existing loft boards and then more loft boards on top of that. The rest I just added normal rolls on top. Easy DIY (I did it!) even if a bit fiddly cutting the insulation board to get into the loft and a littl expensive, but look out for offers. Very effective though
    Originally posted by silverwhistle
    Thanks. I suppose I was hoping that I could just do a quick, inexpensive job of adding an extra 100mm under the existing loft floor boarding without needing to raise the joists or raise the loft board platform. Youíre more keen than me!

    Like you say - another reason is price - the Wickes wool is 3 for 2 at the moment - I think Kingspan etc is much more expensive?

    Is there a cheaper version of the thinner foil blanket type insulation I could add under the existing loftboards without compressing the existing insulation too much?

    Thanks!
    • glasgowdan
    • By glasgowdan 4th Jan 18, 8:22 AM
    • 2,857 Posts
    • 3,201 Thanks
    glasgowdan
    I am about to do the eaves space in my loft as well. There are patches of old fibreglass insulation here and there but I want rid of the stuff as it's so horrible, so I'm going to bag it all up and bin it, then get 300mm of proper insulation in. The eaves covers probably 70% of the ceiling space of the downstairs kitchen, living room and 2x bedrooms, so it'll be worth doing.

    In my case we have some built in storage so I will be adding it on top of everything that's there. In your case, if you think you might be rummaging about in the loft in future I'd get rid of the fibreglass stuff. It makes your skin itch like mad and is just horrible stuff.

    I think it's worth putting as much as possible up there, so definitely get stilts for the boards rather than just putting in 120mm under them.
    • Norman Castle
    • By Norman Castle 4th Jan 18, 10:13 AM
    • 6,851 Posts
    • 5,598 Thanks
    Norman Castle
    Insulation works by trapping air so compressing it reduces its effectiveness. Without an air gap above the insulation condensation can form.
    Don't harass a hippie. You'll get bad karma.

    Never trust a newbie with a rtb tale.
    • Zither
    • By Zither 5th Jan 18, 6:37 AM
    • 330 Posts
    • 41 Thanks
    Zither
    I am about to do the eaves space in my loft as well. There are patches of old fibreglass insulation here and there but I want rid of the stuff as it's so horrible, so I'm going to bag it all up and bin it, then get 300mm of proper insulation in. The eaves covers probably 70% of the ceiling space of the downstairs kitchen, living room and 2x bedrooms, so it'll be worth doing.

    In my case we have some built in storage so I will be adding it on top of everything that's there. In your case, if you think you might be rummaging about in the loft in future I'd get rid of the fibreglass stuff. It makes your skin itch like mad and is just horrible stuff.

    I think it's worth putting as much as possible up there, so definitely get stilts for the boards rather than just putting in 120mm under them.
    Originally posted by glasgowdan
    Thanks - any recommendations for any specific loft stilts? There seems a lot of different brands around and theyíre quite expensive - eg 12 legs for £11 @wickes. My loft space is about 50sqm so I guess Iíd need quite a few?

    Also... are there any resources that quantify how much energy loss would be reduced from going from 110mm >250+ mm of insulation? I totally appreciate loft insulation is worth it but I wonder how much is diminishing returns?
    • Zither
    • By Zither 5th Jan 18, 6:39 AM
    • 330 Posts
    • 41 Thanks
    Zither
    Insulation works by trapping air so compressing it reduces its effectiveness. Without an air gap above the insulation condensation can form.
    Originally posted by Norman Castle
    Yeah thatís what Iíve read too. But then also read that people do it anyway and see an improvement and have no issue with condensation!
    • missile
    • By missile 5th Jan 18, 7:24 AM
    • 9,378 Posts
    • 4,651 Thanks
    missile
    Also... are there any resources that quantify how much energy loss would be reduced from going from 110mm >250+ mm of insulation? I totally appreciate loft insulation is worth it but I wonder how much is diminishing returns?
    Originally posted by Zither
    That calculation would be very difficult. There are many variables which will change on a given application.

    Suffice to say you should aim for a U value of 0.16 W/m2 K or less. In simple terms, 270mm insulation in two crossed layers to avoid thermal bridging.
    See here http://www.rockwool.co.uk/technical-support/tools/U-value-Calculator/
    "A nation's greatness is measured by how it treats its weakest members." ~ Mahatma Gandhi
    Ride hard or stay home
    • Norman Castle
    • By Norman Castle 5th Jan 18, 7:59 AM
    • 6,851 Posts
    • 5,598 Thanks
    Norman Castle
    Yeah thatís what Iíve read too. But then also read that people do it anyway and see an improvement and have no issue with condensation!
    Originally posted by Zither
    I've compresses 6" insulation down to 3". No improvement in insulation. I did it just because its the easiest way to board the loft, I certainly wouldn't add insulation then compress it. If I had more time and patience reducing the compressed 6" insulation down to 3" would probably be an improvement.
    Part of my loft is boarded with plastic coated chipboard. A few weeks ago after cold weather I lifted a few of these and they were wet on the underside.
    Don't harass a hippie. You'll get bad karma.

    Never trust a newbie with a rtb tale.
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