questions about a Lstiburek article on slab insulation

Green Building Q&A: questions about a Lstiburek article on slab insulation

Attached is a figure from a Joseph Lstiburek article on slab insulation, and copied below are two sections of text from the article. I'd be grateful for answers to a few questions. The entire article can be accessed at http://www.buildingscience.com/documents/insights/bsi-059-slab-happy/ 1) "You make the assembly out of three pieces – a footing, a stem wall and the “flat plate” slab part. Then you insulate it under it and on the inside of the perimeter making sure you uncouple the plate from the stem wall at its edge (Figure 1). This edge thing is a big deal – the thermal bridging that occurs if you don’t do it costs you more than half the thermal resistance of the whole deal." Why does a slab lose so much heat at the edge as compared to the underside? In various places the edge insulation is referred to a a "bond break": what does that mean, exactly, and what is the signi...

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