My daughter's father-in-law is a certified residential energy auditor. He is building a new hose in SW MI and wants it to be super tight and efficient ("heat ir with a candle"). After much consideration of alternatives we is going somewhat tradition. Double 4x4 walls. The exterior sheathing is ZIP system, which, once sealed with their tape, provides a very good air/moisture barrier.
The first 2x4 wall is packed with reclaimed polyisocyanurate. It is sealed up against the studs with canned spray foam along with any other cracks. A second 2x4 wall is constructed behind that the traditional kraft faced fiberglass. The blown in fiberglass in the ceiling will be measured in FEET not inches.
(He was going to do SIP, bit the cost of shipping them to his location, the crane and operator and the premium the builder wanted to charge because it would be the first SIP house they ever built, made th cost prohibitive.)
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