Thermal bridges might seem small, but they can be a source of significant energy loss. A superinsulated home is only as good as its resistance to heat flow, and that means addressing thermal bridging during the home’s design and construction. You can pack your home’s walls with insulation, but thermal bridging—places in which the insulation is thinner or nonexistent, such as across a sill or through a wood or steel stud—will cut into your home’s energy efficiency. As the 2013 California Energy Code states, “R-value is used to describe insulation effectiveness, but R-value does not describe the overall performance of the complete assembly,” i.e., the complete wall.
These thermal “short-circuits” primarily occur at the wall framing, where materials with low insulative value, such as wood or metal, help heat escape through the envelope. In conventional stick-frame construction, up to 25% of the wall area can be made up of framing members. The result? Suddenly, the R-value of your “well-insulated” stud-framed wall starts to slide. Add in details like windows and doors, and the whole-wall R-value commonly takes a nose-dive. (You can estimate a building assembly’s whole-wall R-value through Oak Ridge National Laboratory’s interactive calculator at web.ornl.gov/sci/roofs+walls/AWT/home.htm.)
The result is reduced energy efficiency, decreased comfort, and, on cold surfaces, the potential for condensate to develop. So how can you reduce thermal bridges in a home you’re building or one you’d like to retrofit?