Jeff writes from Hermitage, Tennessee: "I have just read with interest the question concerning 2x6 exterior framing vs. 2x4. We are in the design phase with our architect and I am getting conflicting opinions. I had planned to use 2x6 on 16" centers, covered with half-inch ply, then a house wrap and finally with 1 inch foam and then brick. Living in middle Tennessee, we do have prolonged hot summers and I am wondering if it would be more cost efficient to only go with the 2x4 with the foam instead of the 2x6, all other factors being equal. Also, will the addition of the plywood sheathing cause more thermal bridging, or will the rigid foam negate that. I am concerned about structural integrity. Our house will be a two story with an open plan. This will be our 'last' house."

With the 2x4 walls the most R-value you can achieve within the wall cavity with high density fiberglass insulation is R-15. With a 2x6 wall you can achieve R-21 using high density fiberglass insulation within the wall cavity.

The 1" rigid FOAMULAR insulation will greatly reduce thermal bridging.

As far as any structural integrity concerns, those will have to be addressed by your architect. Good luck with your "last" house, Jeff.