Rigid exterior insulation

In case anyone is wondering… our house will have 4″ of rigid insulation on the exterior of the framing and sheathing, topped by vertical furring strips and gigantic screws thru those 4+ inches and into the studs to hold everything up.  And then the siding attached to that.  Just as described here as a “good idea”:  LINK

We are also doing a double-stud wall on the interior, with 2″ of closed cell foam and 9.5″ of cellulose.  “Flash and fill”.  This means we don’t have to do the dew-point calculation to see what the temp of our sheathing is to prevent winter-time condensation (balancing inside and outside insulation) per calc in Joe Lstiburek’s Builder’s Guide to Cold Climates.

That’s an R-value approaching 70 I reckon, a bit lower with thermal bridging, though with 4″ of rigid, we’re in good shape.  Vs R-13 for a typical 2×6 wall filled with fiberglass batts, cellulose, icynene, etc. (R-19 but R-13 after accounting for the thermal bridging every 16″ or 24″ and at the joists.)

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