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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

PLEASE NOTE: A download link for Volume 1 will be sent to you by email and Volume 2 will be sent to you by post as a book.

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    • CommentAuthorBenM
    • CommentTimeSep 16th 2021
     
    Hi,

    We are due to get our roof stripped and retiled.

    Currently, we have fibreglass insulation laid within the void of the roofspace. There is currently 300mm of fibreglass insulation laid out. Originally 100mm, which I then laid an addition 200mm over the top of that.

    I'm wondering whether or not it is worth also insulating with Kingspan (or similar) between the rafters when the roof is stripped?

    Any info or advice would be much appreciated.

    Regards

    Ben
  1.  
    On the assumption that the roof void is ventilated there is no point in putting insulation between the rafters as this would be above the ventilated space so any gains would be lost.
    However when the roof is stripped it is a good (easy) time to pay attention to the eaves detailing re insulation and air flow.
    Oh and make sure the contractors don't stomp all over your nice 300mm glass wool reducing it to useless.
    • CommentAuthorrevor
    • CommentTimeSep 16th 2021
     
    If there is enough room to create a living or working space up there? if so you could the consider between rafter insulation and over rafter insulation and get rid of the glass wool insulation.
    • CommentAuthorBenM
    • CommentTimeSep 16th 2021
     
    Posted By: Peter_in_HungaryOn the assumption that the roof void is ventilated there is no point in putting insulation between the rafters as this would be above the ventilated space so any gains would be lost.
    However when the roof is stripped it is a good (easy) time to pay attention to the eaves detailing re insulation and air flow.
    Oh and make sure the contractors don't stomp all over your nice 300mm glass wool reducing it to useless.


    That's interesting. What should I be looking out for? Should new vents be inserted?
    • CommentAuthorBenM
    • CommentTimeSep 16th 2021
     
    Posted By: revorIf there is enough room to create a living or working space up there? if so you could the consider between rafter insulation and over rafter insulation and get rid of the glass wool insulation.


    It's not got the height to have a living space up there, unfortunately.
  2.  
    Eaves vents with roughly 25mm clear opening each side. Watch out for 'windwash' (cold air getting in-between the layers of insulation) at the eaves. A membrane laid across the insulation might help.
    • CommentAuthortony
    • CommentTimeSep 17th 2021
     
    If it was mine, golden opportunity to insulate over the wall plate, leave 25mm gap above insulation and insulate down to soffit or to join wall insulation

    Totally sort out and tidy hard to access bits

    I would do another 100mm over the top too while it is so easy to do
    • CommentAuthorbhommels
    • CommentTimeSep 17th 2021
     
    Posted By: tonyIf it was mine, golden opportunity to insulate over the wall plate, leave 25mm gap above insulation and insulate down to soffit or to join wall insulation

    Totally sort out and tidy hard to access bits

    I would do another 100mm over the top too while it is so easy to do

    +1
    If you have the chance go for a warm roof. A bit more work for the roofers but definitely worth it. I wish I could have done this but I'm in a semi.
  3.  
    Posted By: bhommelsIf you have the chance go for a warm roof. A bit more work for the roofers but definitely worth it.

    And quite a bit more expense plus most (all?) of the existing loft insulation redundant and great attention to detail needed from the roofers to prevent gaps around the edges or anywhere else which will nullify the insulation
    • CommentAuthorbhommels
    • CommentTimeSep 17th 2021
     
    Posted By: Peter_in_Hungary
    Posted By: bhommelsIf you have the chance go for a warm roof. A bit more work for the roofers but definitely worth it.

    And quite a bit more expense plus most (all?) of the existing loft insulation redundant and great attention to detail needed from the roofers to prevent gaps around the edges or anywhere else which will nullify the insulation

    In my experience, the fewer details with a warm roof are much easier to get right than those of a cold roof. ymmv.
    The OP is considering insulating between the rafters, so that expense is already factored in, and that would partially nullify the existing insulation. The additional expense & work is going to be counterbattens and fixings.
    • CommentAuthortony
    • CommentTimeSep 18th 2021
     
    Warm roof increases the heated volume and surface areas both are downsides, worse is potential for air leakages into warm loft wasting even more energy
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