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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    • CommentAuthortony
    • CommentTimeNov 21st 2011
     
    I am seeing a local industrial estate being re roofed

    They are using nice insulated laminates steel profile sheets

    But on top of the existing uninsulated profiled sheeting

    This leaves an air gap between the new and existing 80% of the area

    This is a winter cooking system making the insulation of very little value -- anyone else seen this going on?
    • CommentAuthorJeff B
    • CommentTimeNov 21st 2011
     
    Tony - I don't understand your point. Aren't they simply making an insulation sandwich (assuming the profiles interlock exactly)? I assume they are taking out the old fixings as they go and putting new ones right through both old and new sheets?
    • CommentAuthorCWatters
    • CommentTimeNov 21st 2011
     
    Air gap is ok as long as it's not ventilated!
    • CommentAuthorTimber
    • CommentTimeNov 21st 2011
     
    ^ All air voids will allow some convection of air, and this is likely to move air from warm to cold areas.

    I think you are right Tony, similar to adding a warm flat roof, and not sealing the joist voids, as per the thread on here.
    • CommentAuthortony
    • CommentTimeNov 21st 2011
     
    There are full length gaps eaves to ridge with no sealing anywhere between the old and new

    The undersides of the new sheets are flat and the top of the old are standing seam/ profiled.
    • CommentAuthorJonti
    • CommentTimeNov 23rd 2011
     
    Maybe it is to keep the heat out in summer:bigsmile:
    •  
      CommentAuthorjoe90
    • CommentTimeNov 23rd 2011
     
    Maybe its a cold store!
    • CommentAuthorCWatters
    • CommentTimeNov 23rd 2011
     
    Posted By: Timber^ All air voids will allow some convection of air, and this is likely to move air from warm to cold areas.


    If the ends were sealed properly an extra air gap could only improve insulation over one without. eg An air gap never has a negative thermal resistance.


    Posted By: tonyThere are full length gaps eaves to ridge with no sealing anywhere between the old and new The undersides of the new sheets are flat and the top of the old are standing seam/ profiled.


    Perhaps they plan to seal the edges later? Otherwise I agree it doesn't make much sense.
    • CommentAuthortony
    • CommentTimeNov 23rd 2011
     
    The finished roof with scaffold gone aint been sealed
    • CommentAuthorTimber
    • CommentTimeNov 24th 2011
     
    ^CWatters - While I agree in principal, unfilled air voids on the warm side of the thermal envelope are nearly always bad news.

    If it were me, I would lay dense mineral wool batts between the profiled lower roof, before the upper roof is installed and still seal the edges of the voids.
    • CommentAuthorBen1974
    • CommentTimeNov 24th 2011
     
    Interestingly they are doing carry out work on the roof of the swizzles sweet factory over the road from me. Wool is being rolled out over the top of the old asbestos roofing and new sheets screwed through onto 2*3 scant. Looks like there are quite a lot of gaps in the wool as it's being installed so not sure who good it will be in practice!
  1.  
    Ben1974 wrote - Interestingly they are doing carry out work on the roof of the swizzles sweet factory over the road from me. Wool is being rolled out over the top of the old asbestos roofing and new sheets screwed through onto 2*3 scant. Looks like there are quite a lot of gaps in the wool as it's being installed so not sure who good it will be in practice!

    Is it for insulation or as a soft filler to prevent the old and new sheets interfering with each other and cracking as they are screwed together?
    • CommentAuthorBen1974
    • CommentTimeNov 24th 2011
     
    I'm pretty sure it's for insulation. I could shout over the road to them and ask!

    Some of the old roof is pink from all the coloured sugar dust that is blown out of the top. If you wanted to live near a factory you couldn't choose a better one than a sweet factory. The smell isn't overpowering apart from along the canal tow path near some of the extractors. The air there is hot and sickly sweet. I go running sometimes, if that's the last bit of a route and you're hanging out it makes you want to throw up.
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