Steve writes from Kitchener, Ontario, Canada: "I'm renovating my 115 year old, double wythe brick house. Construction of the exterior walls is 2 wythes of brick with embedded 2x4's and 1"x2" strapping. We added additional 2x2's to the strapping to create approximately a 2.5" to 3" stud space for insulating. If I use the R-13, 3.5" batt insulation, how much will the R-value be reduced if it's compressed to the minimum 2.5" thick?"

Answer: There is a Compression Chart on the Owens Corning Web site that indicates the R-values that result when insulation is compressed in a cavity. In your case, the R-13 insulation you plan to install will be reduced to R-10.