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Hi Bill, Great work! It's fantastic to see these issues getting discussed. I was wondering - could the thermal bridge be reduced by using a discontinuous steel angle upon which you mount a 50x50 batten? The batten could support the threshold. This would allow the concrete slab to be cut back thereby allow greater continuity of the insulation. Whilst remembering that timber performs about four times worse than your insulation it is about ten times better than the concrete. The benefit of this solution would also be to raise surface temperatures which would avoiding condensation risk and mould growth. Of course using the detail that I've suggested you could just the door moved forward – rather than cutting the concrete back – but this would not have such a significant impact upon heat loss (the benefit to surface temps would probably be affected to a lesser extent.) By now it may be to late to make this suggestion....