Tom writes from Philadelphia, Pennsylvania: "Could you please offer your professional opinion? I am in the beginning stages of siding the back of my brick row home. I was originally going to attach furring strips to the brick wall and use rigid insulation before I attached the siding. My question is would it be more energy efficient to have larger than a 3/4" air gap behind the insulation? Also, with regard to my Zip code, can you please recommend the proper size insulation (1/2" or 3/4") for my project?

Answer: I recommend 3/4 inch PINK foam insulation and there really is no advantage to going with a bigger air space.