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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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Housing - New Build: Insulation on the outside = smaller footprint for foundations?

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  1.  
    • CommentAuthorRobinB
    • CommentTimeMay 18th 2009 edited
     
    If I put all my insulation on the outside of my building can I have smaller foundations?
    Won't that save loads of concrete, digging and money?
  2.  
    Yes,
    perhap not " loads of money " though.
    • CommentAuthorjon
    • CommentTimeMay 18th 2009
     
    Sometimes but not often

    Depends on the ground conditions. It won't save much money though.
    • CommentAuthorMike George
    • CommentTimeMay 18th 2009 edited
     
    I think you can [subject to ground conditions]. As far as I know Part A stipulates foundation width as [cavity] wall thickness + 150mm overhang both sides, so a 2x100mm masonry wall having a clear cavity of 50mm can in theory have a strip width of 550mm Traditionally though 600mm has tended to be used.

    Now that cavity walls are starting to be built at 300mm plus there will be a clear advantage to using external insulation, particularly where space is tight on a development site, ie this may mean an extra house can be built as the footprints are smaller. Perhaps even 225mm solid walls are possible having a foundation width of 525mm?

    That's without considering the saving in digging, exporting spoil from site, extra concrete etc
    • CommentAuthorjon
    • CommentTimeMay 18th 2009
     
    That's just the bucket width though Mike? We regularly go down to 450 (sometimes 400) using traditional with the larger developers that want to cut it to the bone (subject to ground)

    I see the point though: Rather than "sometimes, not often", just sometimes?
  6.  
    Hmm, I thought you could only go down to 450mm width for trench fill?

    Where I am it's rarely anythng other than 600mm strip. [Lots of clay here]
    • CommentAuthorMike George
    • CommentTimeMay 18th 2009 edited
     
    Just checked an old Part A I have.Now I've read it properly I can see that the 150mm is depth not width :shamed:

    Still not much chance of getting the width down to 400mm in my area. The BCO allways asks for 600mm
    •  
      CommentAuthorfostertom
    • CommentTimeMay 20th 2009
     
    Posted By: Mike GeorgePerhaps even 225mm solid walls are possible
    Maybe even 140 block if the engineer can OK it - with bracing/butressing from return walls/angles/partitions. Building suddenly gets much simpler, with EWI, after decades of progressive complication.

    Strangely, though, returning to strip founds as part of the package, so EWI can be taken down deep to top of strip found. You can still have a narrow conc strip found at the bottom of a wider trench. As conc and blockwork get more expensive, once fuel price rise resumes, this will be the way to go - narrowest poss strip found with narrowest poss single skin blockwork, EWI'd. No more trenchfill.

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