I’m in NH (CZ 6A) doing an exterior remodel on my 1950 ranch using 7 1/4″ Larsen Trusses over a 2×4 structural wall.  The existing wall is standard drywall, 2×4 studs, FG batts and 3/4″ board sheathing.  I’m removing the tar paper, adding trusses and will sheath with Zip.  The trusses will extend down below the outer rim joist.  The house has generous 30″ overhangs.  I’m planning to insulate with TimberHP batts with loose fill to pack cavities.

In one area, I’m adding a deck and will align the deck joists with the trusses in order to insulate over the ledger.  Because of the greater potential for water intrusion from splash back, snow build up, etc.  I’m thinking of using Rockwool batts for the lowest 2′ due to the proven effectiveness in potentially wet environments.

My question, if I sheath and seal appropriately under and between the deck joists, anyone see an issue using 2′ of Rockwool in the lower bays with 6′ of TimberHP in the upper portion of the wall bay?