Carl writes from Kittery, Maine: "I have a knee wall insulated with r15 and i had to get behind it to do some work. Code in my area is now r19 - do i have to rip out everything, furr the knee wall studs and reinstall r19 or can i just put foamular board on the back side (facing the cold air space) to increase the R value, or would it create a double vapor barrier (from the inside out it would look like this:(sheetrock/kraft paper/r15/foamular)."

Answer: FOAMULAR® Insulation is not a product we recommend on the back of a knee wall. The use of rigid foam in that situation may lead to condensation on the front of the product. We recommend adding unfaced FIBERGLAS™ Insulation. This may require insulation supports or netting.