The type of batt insulation that is typically installed between 2×6 studs has a nominal rating of R-19, R-20, or R-21, depending on the type of insulation used and the batt density. If you install R-20 or R-21 fiberglass batts between 2×6 studs, you can meet the minimum R-value requirements for walls specified in the prescriptive tables in the International Residential Code, assuming you live in Climate Zones 3, 4, or 5.
But if you live in Zone 6, 7, or 8, this type of wall no longer complies with the code. Similarly, builders in British Columbia, Canada, need walls that exceed R-20 — they now need to hit at least R-22.
To help Canadian builders build R-22 walls, the city of Vancouver and the province of British Columbia have jointly published a useful construction manual called “Illustrated Guide to R22+ Effective Walls in Wood-Frame Construction in British Columbia.” The well-illustrated manual has been posted online, where it is available at no charge.
The document’s principal author is Lorne Ricketts, an engineer at RDH Building Science. (I’d like to tip my hat to GBA reader Malcolm Taylor, a Canadian builder who first alerted me to the existence of this resource.)
The manual provides advice on constructing walls that have a whole-wall R-value of R-22 or more. So what’s an R-22 wall? According to the manual, what matters is whole-wall R-value, not the R-value stated on the insulation package. The manual’s method for calculating whole-wall R-values takes into account the effect of framing lumber; it assumes that a wood-framed wall has 16-inch-on-center studs and a 23% framing factor.
The online manual has good advice, clear illustrations, and useful fastening schedules for installing furring strips over rigid foam — in other words, valuable information for almost any cold-climate builder, whether Canadian or American.
The manual provides guidance on the…