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Re: Slab & Frost heaves?
From the WFO board
Posted by douglas Brown
In Reply to: Re: Slab & Frost heaves? posted by Klaus
I live in Canada and we use the floating slab method for many different types of construction (both heated buildings and unheated sheds). The insulation you are suggesting will not be of any use in this application as it is closer in concept to an unheated shed. A floating pad will rise in the winter and lower back down after the frost leaves - what we want is for it to do it consistently over the pad. This will happen on the pad Rado has designed but in order to ensure that it is consistent you must put a layer of clear stone(3/4 inch crushed washed stone)underneath the pad to at least a depth of 4 inches. This allows for water to be taken away from the area directly under the pad - you must also have a route for the water to flow - ie good drainage.
If you were building a heated building - you would need the insulation at the edges as you described as your building heat would keep the layer under the center of the pad from freezing and the outside of the pad would be affected by the freezing ground and you then would have an inconsistent amount of frozen ground underneath. But our pad is not heated as the heat from the oven is well above the ground and the open wood storage area will let the cold affect the whole foundation. So actually the insulation might do more harm than good.
The 12" depth of concrete around the perimeter is a good idea - and perhaps you might want to go as deep as 18". These concrete beams are what keeps the pad strong(and the re-inforcing bar Rado insists on is critical )The pad WILL rise and WILL fall as the seasons cycle. It is important that as this happens the pad should not break . Thus the concrete beams are almost as important as the clear stone bed(or cushion) below.
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