A thermal bridge is a component within an envelope assembly that short circuits the insulation and allows more heat loss than the surrounding insulation.
The effective RSI accounts for the thermal-bridging effect of closely spaced, repetitive structural members (studs and joists) and other structural members (lintels, sills and plates). These interrupt the thermal resistance of the cavity insulation. For example, an RSI 3.87 (R22) cavity insulation has an effective RSI of 2.55 (R14.5), based on 2 x 6 framing at 16” o.c. studs.
The map illustrated below shows the ranges in Heating Degree Day (HDD) across Western Canada. HDD represents the number of degrees that a day’s average temperature is below 18° Celsius (65° Fahrenheit), which is the temperature below which buildings need to be heated. The higher the HDD, the more frequently that area of the map has days where a home requires heating. Not surprisingly, most of Western Canada falls in zones with a high HDD, therefore increasing the importance of building well-insulated homes. This circumstance is increasingly reflected in updates to local and national building codes.
