What is thermal bridging and why is it important that we pay close attention to its effects in the homes we build?

The importance lies in the different materials we use to build our wall systems, how much of these materials we use and what conductivity these materials have. We all know that exterior walls have (or should have) insulation, and its purpose is to slow down movement of heat through our walls.

Most of you know about the R-value of insulation materials. R-value rates the materials’ resistance to heat-transfer: the higher the R-value, the lower the heat-transfer. The illustration above best shows how the different materials in the walls affect heat transfer.

We also know that most of our wall assemblies in residential construction are built with wood studs and wood sheathing on the exterior. Soft woods have almost 3 times the conductivity rate of fiberglass insulation, so heat transfers much more quickly through the parts of the wall assembly that are made out of wood, essentially bypassing the insulation. This process is called "thermal bridging" and it results in a lower overall R-value of your wall assembly. Most people mistakenly think that because they insulate their wall with R-19 fiberglass insulation, they have an R-19 wall, when in reality their wall has a much lower effective R-value.

What does that mean from a practical standpoint? Well, let’s put it in the simplest way possible: the more wood studs in your wall assembly, the lower the R-value of your wall.

How can we solve this and make our wall assembly more energy efficient? Obviously, by using less wood in our walls to allow for less thermal bridging and more insulation in the assembly.  But how exactly can we achieve this? There are several ways: we can use systems like SIPs (structural insulated panels), ICFs (insulated concrete forms) or use advanced framing techniques. I will post follow-up articles on all of these solutions in the coming days.

Links to other articles in this series:

Exterior Wall Assemblies… or “How to build a better house” – Part2 of 7

Sources: BuildingGreen.com , BuildingAmerica.gov , eeba.org

IMAGE CREDITS: Illustration by Julia Jandrisits