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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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Building Regulations and Standards: Insulation

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  1.  
    • CommentAuthordaveh38
    • CommentTimeMar 9th 2010
     
    Hi everyone, 1st time on the forum, so I hope I am doing things correctly.
    I am in the process of renovating and extending 3 of 100 year old farm workers cottages, which are now 1 cottage.The outer walls are 9" solid brick, which I have now dry lined with 25mm Kingspan and plasterboarded .I am just about to start insulating the loft conversion/roof space. The roofspars are now 170mm x 50mm at 400mm centres (approx). I was going to insert 100mm Kingspan (or similar) and under draw with another 25mm bonded on to 12.5mm plasterboard. It has been suggested that I use 2 x 50mm layers of Kingspan, so that any joints can be staggered to provide a better covering.Can anyone comment on this, or indeed suggest a better way of insulating.
    • CommentAuthorwookey
    • CommentTimeMar 9th 2010
     
    Not much pont staggering the 100mm PUR between the rafters if you are putting a thermal board on the inside - that should close over the joins. 125mm PUR is reasonable insulation but not great for a roof. Go thicker if you can. If you have 170mm depth rafters then 120mm of PUR in there would be good. Then another 80 on the inside would get you to around U of 0.14 which is quite good.

    25mm PUR lining on the walls is much much better than nothing but you'll probably regret doing it so thin in a few years. 50mm or 100mm would be much better. Probably a bit late to change that now.
    • CommentAuthorJeff B
    • CommentTimeMar 9th 2010
     
    I agree with Wookey's comments. Pity you had not posted on the forum earlier before you actually started the work, as 25 mm of Kingspan as internal insulation is really not sufficient. I have used 75 mm on my walls. Perhaps you could not afford to lose so much room space?
    • CommentAuthortony
    • CommentTimeMar 9th 2010
     
    Are you in the UK? most of our building regs require much more insulation than you are proposing and it would be far better to go way better than the minimum.
    • CommentAuthordaveh38
    • CommentTimeMar 10th 2010
     
    Greatv comments. I was restricted to 25mm insulation on the outside walls. when I added the 12.5mm plasterboard, I was in danger of coming up to the reveal of a window on the adjacent wall. Local building control suggested 170mm rolls of fibre insulation in between the roof spars. my understanding is that 100mm pur gives greater insulation. What is the calculation between pur and rolls of loft insulation?
  6.  
    Posted By: daveh38What is the calculation between pur and rolls of loft insulation?

    It depends upon the loft insulation & the PUR board. However, 100mm of typical PUR (k=0.023) is roughly equivalent to 200mm of the cheapest loft roll (k=0.044), 170mm of medium quality loft roll (k=0.040) or 140mm of good quality rafter roll (k=0.032).

    I would put 170mm of Knauf Rafter Roll 32 between the rafters & 50mm PUR below them. The rafter roll is vapour open & will prevent moisture being trapped in the rafters, while the PUR will prevent cold bridging. Overall U value about 0.16.

    David
    • CommentAuthordaveh38
    • CommentTimeMar 11th 2010
     
    good suggestion david. as I am struggling for space in the loft conversion, would it be an advantage to use one of the new foil/space blanket rolls instead of the 50mm PUR ? How would this affect u-values ?
    • CommentAuthortony
    • CommentTimeMar 11th 2010
     
    • CommentAuthordaveh38
    • CommentTimeMar 12th 2010
     
    point taken. thanks
  10.  
    Posted By: daveh38as I am struggling for space in the loft conversion, would it be an advantage to use one of the new foil/space blanket rolls instead of the 50mm PUR ? How would this affect u-values ?

    I am not a fan of multi-foil insulations. Airtightness at laps & perimeter are critical to getting it to work & most real world installations will not be airtight, especially as air gaps are required both sides. If you're planning a service cavity, you can get a benefit from using a single foil layer as your air barrier, but it's more expensive than polyethylene & interferes with mobile phone & radio reception.

    Given that typical multi-foils are 20-25mm thick & 20-25mm air gaps are required both sides, the PUR solution may end-up being thinner. If you want to go thinner still there is always aerogel, but this is extremely expensive & generallly only used for dealing with cold bridges.

    David

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