Above Grade Walls

The effects of thermal bridging in wood framed walls

Wood has an R value of about one per inch of thickness, as opposed to fibreglass insulation that is about 3.3 per inch. When you sit down and do a careful analysis, there is a lot of wood in exterior wall construction. A stud occurs every 16", there are two top and one bottom wall plates, additional framing is installed over and at the sides of window and door openings, not to mention extra framing at each corner and interior wall intersection for the attachment of drywall. In some cases, up to 20% of the area of an exterior wall can be solid wood. Since a 2x6 has a thermal value of about R-5, the wood areas of the wall have the effect of reducing the advertised R-20 wall to an overall performance of anywhere between R-14 to R-16.