The design to remodel an old concrete block building into our future home in Hillsborough, NC (climate zone 4A) is finally taking shape and I would like to get your help and feedback on some of the energy related decisions.  We would like to approach the remodel with “net-zero” energy (with solar cells) in mind and do this sensibly and as cost efficiently as possible.

Walls:  The walls are currently uninsulated concrete blocks.  My plan is to parge the exterior (low cost and durable WRB) and build an interior 2×4 wall to mount the drywall.  I am also leaving a 4-1/2″ gap between the block and the 2×4 wall allowing for a total of 8″ insulation space.  Based on what I understand, it appears that I should first spray 2″ of closed cell foam against the concrete blocks to seal against any moisture and act as air barrier.  Then, for the rest of the wall cavity, I believe high density cellulose should be the most cost-efficient insulation.  Total R-value would be about 32.  Painted ½” drywall on the inside would act as vapor barrier.  A few questions:

·        Instead of the 2” sprayed closed cell foam, would a liquid applied WRB on the block wall (plus additional cellulose) be a better choice for the water and air barrier?

·        Should I leave a bigger insulation gap (and sacrifice interior space) to increase the wall R-value further?

·        Is the painted drywall good enough of a vapor barrier or do I need to install another layer of vapor retarder under the drywall?

·        Anything else I missed?

Roof/Ceiling:  The roof is currently made from common and scissor trusses.  They do not have raised heels.  I intend to keep a conventional vented attic.  I intend to install vent baffles (SmartBaffle) and insulate the ceiling with 16” of cellulose (R-60).  The R-value towards the edges of the roof will be lower due to lack of raised heels.  Questions:

·        Is the painted drywall good enough of a vapor barrier or do I need to install another layer of vapor retarder under the ceiling drywall?

·        Is 16” of cellulose enough, just right, or an overkill for zone 4A?

·        Anything else I missed?

Floor:  The current floors are uninsulated concrete slabs with a 4” step.  As we want a level wood floor (no trip hazards, no hard concrete to stand on) we will raise one floor with 5-1/2” joists and the other with 1-1/2” “joists” and ¾” OSB subfloor.  I intend to put down 10 mil plastic sheeting for vapor barrier and then insulate with 1-1/2” EPS boards between the joists.

·        For the 5-1/2” joist space, I could add more insulation.  Does it make sense to install more EPS in the floor?

 New Walls:  We will be adding some more space.  For the new walls, I was intending to use 2×6 walls.  However, 2×8 yellow pine is cheaper than 2×6 SPF; so now, I am planning to use 2×8 yellow pine for the walls.  This will be a bit less expensive, and it will also allow more room for insulation. Has anyone else done this?  Are there any issues with using yellow pine for walls? 

 Thank you for any thoughts and wisdom you can provide.