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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.

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    • CommentAuthorstephendv
    • CommentTimeAug 7th 2010 edited
     
    I need a low impact foundation system for our wood cabin which has a 12mx4m base. All the builders I've spoken to have suggested concrete footings, 60cm square with concrete pilars on top, 5 under each 12m glulam beam. Besides involving lots of concrete and being time intensive (have to build a form for each pilar), it will also be very difficult to remove, if we ever decide to remove/move the cabin. The other option they've mentioned was concrete piles using a cardboard/plastic tube as the formwork - but these tubes are quire pricey for being disposable.
    Are there any other options?

    The soil is more sand than clay.

    EDIT: I should also mention that there's a 1m difference in height between the shortest pilar and the tallest.
    •  
      CommentAuthorjoe90
    • CommentTimeAug 7th 2010
     
    How about telegraph poles buried in the ground then cut off at right height and bolted to glulams???
    • CommentAuthorjon
    • CommentTimeAug 7th 2010
     
    Wood cabins are usually very light. Generally, the critical design criteria of foundations is based on settlement rather than failure. However, if there's a significant slope on the site, this might not be the case. If you know the weight of your cabin, you could suggest to the BCO (if it's a BCO overseeing) that you simply strip off the equivalent weight of soil and then make "foundations' from paving slabs with bricks over (and use large hardwood wedges that can be re-adjusted if problems occur).

    It would need some care, but there's no technical reason why this couldn't be done, particularly if you have a sandy soil.
    •  
      CommentAuthordjh
    • CommentTimeAug 7th 2010
     
    A few random thoughts since nobody's mentioned them:
    - You can use a plastic bucket or large flower pot as a mould to cast the concrete pillars.
    - The concrete pillar only needs to be short with a metal bracket from its top and then you can use timber for the 1m height.
    - You could use tyres or earthbags (perhaps with some cement in the earth) instead.
    - You could use stone, if there's any around.
    • CommentAuthorchuckey
    • CommentTimeAug 7th 2010
     
    Is the 1 m slope across the 4 or 12 m dimension? if its the 4m, the I would reckon that you need to get down to the subsoil. Else I would reckon that a couple of feet would do. I like the sound of the telegraph poles, should be good for 30 years.
    Frank
    • CommentAuthorstephendv
    • CommentTimeAug 8th 2010
     
    Thanks for all the suggestions. I like the telephone pole idea too - now just need to fine some...
    The slope is in the 12m direction and I have to hire a mini-digger to dig a trench for water and electricity anyway, so getting an auger attachment won't add much to the cost.
    • CommentAuthorfinny
    • CommentTimeAug 8th 2010
     
    Why are you wanting to sink timber in the ground? auger like you say, backfill with 25-50 mm stone, add wand vibrator usually used for screed to settle out and lock the stone, then put paving slab on top. any timber post you start your cabin with can take up the height difference between pavers, saving you the bother of trying to sit them level..:cool:
    •  
      CommentAuthorjoe90
    • CommentTimeAug 8th 2010
     
    •  
      CommentAuthorfostertom
    • CommentTimeAug 8th 2010
     
    Fencing contractors can sink a 8"sq oak gate post 4ft deep in 15mins, using various techniques incl. tractor-mounted auger.
    • CommentAuthorbene
    • CommentTimeAug 11th 2010
     
    2nd hand sleepers are around 2.7m are often oak and have been dunked in nasty creosote (last longer than you will)
    we've used these for piles with a mix of clay/sand/and a good dash of hydrated lime rammed around them.
    if there is any clay at all or if you can easily get it. it might be worth reading these...

    http://www.lime.org/uses_of_lime/construction/soil.asp
    http://www.graymont.com/pdf/Soil_Stabilization_Brochure_En_05_06.pdf

    worked great - we went in about 1m, although on flat ground and a building roughtly half the size of yours.
    • CommentAuthormuhyiddin
    • CommentTimeOct 12th 2010
     
    This is probably too late, but when I built my office and studio last year, we levelled the ground and built a frame from 50x100 timbers on paving slabs on sand on type 1 stone. It works fine.

    The other option is helical steel piles which can be taken away and recycled when the building is removed.
    •  
      CommentAuthorfostertom
    • CommentTimeOct 14th 2010
     
    Posted By: muhyiddinon type 1 stone
    How deep/wide - filling in a trench? How to get below the frost heave depth?
    Posted By: muhyiddinhelical steel piles
    What cost to install? - any links? What cost to unscrew and recycle?
  1.  
    Don't bother with concrete, use a steel screw post such as http://www.technometalpostusa.com/index.php?page=metal-post or http://www.pieuvistech.com/html/en/home.php

    This latter type is what we used for a wrap-around porch/deck and it's cheaper, faster and easier to install than concrete sonotubes.

    Paul in Montreal.
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