Peter writes from Mount Vernon, New York: "We have an old house (1920) that is of balloon frame construction and was uninsulated. Our kitchen has outside walls on 3 sides and is extremely cold in winter. The outside walls are stucco, 3/4" 1x6 T&G sheathing and true 2x4 wall studs and lath and plaster inside finish. We are remodeling and have removed the lath and plaster and will be insulating the walls and replacing all the windows. Our idea to maximize the R value (and use up the full 4" of wall cavity) was to use 1/2" or 3/4" Formular board on the inside of the sheathing and use spray foam (with minimal expansion) to seal the edges of the Formular. We would then install 3 1/2' R-15 FG batts with kraft vapor barrier and finish with 5/8" drywall. Does this make sense and will it be worth the effort? I have not heard of anybody doing this. By the way, I have not been able to locate the R-15 3-1/2 FG batts at my local big box home stores. Can you supply me with suppliers?"

Answer: You will want to make sure the foam you use is extruded polystyrene safe, which generally means it is not petroleum based. If the foam is not compatible, I recommend instead using BILD-R-TAPE® construction tape on the seams of the FOAMULAR® insulation board. Any place that sells Owens Corning insulation should be able to order the R-15 if they do not have it in stock. There is a dealer search at www.itseasytoinsulate.com.