Numbers Don't Lie: 71 Things You Need to Know About the World

by Vaclav Smil

Once energy prices began to rise and more rational building codes came into effect in North America, it became compulsory to incorporate plastic barriers and fiberglass batts—pillow-like rolls that can be packed between the wooden frames or studs. Higher overall R-values were easily achieved by using wider studs (two-by-six) or, better yet, by double-studding, which involves building a sandwich from two frames, each one filled with insulation. (In North America, a softwood “two-by-six” is actually 1.5 by 5.5 inches, or 38 by 140 millimeters.) For a well-built North American wall this means adding insulation values of drywall (0.5), polyethylene vapor barrier (0.8), fiberglass batts (20), fiberboard sheathing (1.3), plastic house wrap (Tyvek ThermaWrap at 5), and beveled wood cladding (0.8). Adding the insulating value of interior air film brings the total R-value to about 29. Brick walls, too, got better. To keep a desired outer look of colored brick, an old wall can be retrofitted from the inside by putting wooden battens (thin strips that hold insulation in place) on the interior plaster and attaching insulation-backed gypsum board integrated with a vapor membrane to keep out moisture. With 2-inch insulated plasterboard, this will triple the previous overall R-value, but even so, the insulated old brick wall will remain an order of magnitude behind the two-by-six framed North American wall. Even people who are generally aware of R-values do not expect to see such a large...