It is a requirement of the Building Code that dwellings built with slab on ground construction and fitted with in-slab heating "must have insulation installed around the perimeter of the slab". The insulation is required to be waterproof, have an R value of not less than 1.0, and to be continuous from the from finished ground level to a depth of 300mm or the full depth of the vertical slab edge (whichever is greater, presumably). Reference BCA 2009, 3.12.1.5.
However it seems that this clause is often ignored by designers/architects and building inspectors.
I'm building as owner builder and have had to grapple with some of the issues noted in previous posts. The house it at slab stage only, with hydronic heating pipes and manifold installed.
My gut feeling was to insulate the slab edge only, and not insulate underneath, on the basis that I was tapping into a big heat reservoir that would be of more benefit that harm. The (smallish) firm i engaged for my slab work had never before encountered a customer who persisted in wanting slab edge insulation - (after some 15 years in business). So it was a bit like the blind leading the blind ....
I went for 50mm (R1.7) extruded closed cell polystyrene sheets 600mm x 2400mm, which were laid on edge - outside the formwork. In reality it is not as simple to do as you see in all the pretty diagrams; which, I suppose, is one reason why it is generally not done.
If I had my time over, I think it might have been better (i.e. neater) to have the setout adjusted so that the foam sits inside the formwork? However the concreter did say that this would have required a lot more work with the formwork and probably cost an extra day of their labour.
There is certainly more to this than meets the eye and I wont try to cover anymore now, but am happy to try and answer any specific questions.
cheers,
John
Posted Tuesday 20 Jul 2010 @ 2:31:46 pm from IP
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