Warning: For Energy Nerds- Wall Energy Rating

All of us in the energy efficiency business know that building assemblies depending on fiberglass for insulating value almost never function at the nominal R value theoretically obtainable by a given thickness of fiberglass. We see a lot of attics with 5-1/2" fiberglass batts bearing a stamp on the label of R-19 that in fact function at R-5 or less. If you've never seen the BPI guidelines for the value of existing insulation, you might be surprised. (At least in an attic you can improve the situation pretty easily with blown-in cellulose.) But how about an existing stud wall? There's no room for any more insulation. Canadian building scientists are trying to develop a new thermal rating system for walls called, appropriately enough, wall energy rating. The purpose of this rating is to more realistically reflect the thermal resistance of wall assemblies subject to air infiltration.