I live just outside the Seattle area and am building my home. It is a three story, on grade, 3750 sq ft structure. I'm planning on using two separate furnace units - an electric heat pump for the third floor and a gas fired unit for the other two - so that I can better control the zones as well as avoid ducting chases through the open floor plan of the second floor. The third floor is mostly vaulted ceilings and my plan was to run the ducting in the 2x12 rafter bays but I'm wondering if condensation would be an issue.
Structure from the outside in = standing seam metal roof, underlayment, 5/8" CDX, 1 1/2" air gap, 1" foil faced poly iso as a baffle edges and seams sealed with foam, Blown in John's Mansville BIBS insulation on 2x12 rafters.
If anyone has suggestions or experience I would love to hear ideas or input.