Slab insulation advice

It’s a good idea to insulate your slab if mechanical heating or cooling is needed in your home, says sustainable design expert Dick Clarke.


My wife and I are about to self-build in Araluen, New South Wales. We are still in the design phase and want to build with passive solar design principles. We are going for a highly insulated, reverse veneer, slab-on-ground construction.

In Sanctuary 21 there is a design workshop article with a response by Graham Hunt, which I liked. In it he recommends fully insulating the underside and edges of the slab, however I have also read that this is not necessary except in the most extreme climates as it negates the effect of earth coupling. Can the panel please comment on earth coupling and slab insulation?

— Richard


Great controversial question, Richard. While debate is ongoing on this subject, the scales have tipped in favour of insulation in all but really mild climates – Araluen is not mild. Therefore I would insulate (note that in 1986 I would not have – this is the evolution of knowledge).

From a more technical point of view, the decision to insulate the underside of a slab goes hand in hand with whether any energy is needed to heat or cool your home. If not, no insulation is needed. A designer or energy performance assessor can use energy rating software tools to give you this info.

—Dick Clarke

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Cover of Issue 22
You can read more about Slab insulation advice in Issue 22 of Sanctuary magazine.

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