Thermal Bridging Short-circuits Your Insulation

In a typical stick-frame house, lumber occupies 27% of the wall area, leaving little room for insulation. Since the insulating value of softwood lumber (R-1.25 per in.) is less than that of fiberglass or cellulose insulation (R-3.6 per in.), each stick of wood lowers the wall’s overall R-value. Each piece of framing lumber acts as a thermal bridge, a conduit for heat to leak through the wall. Thermal bridging is more significant than many realize. This interactive graphic illustrates how heat flows around insulation and through the framing members in a wall, roof, or floor. It also shows you how to interrupt this heat flow with rigid insulation.

How it Works: Thermal Bridging Another benefit to covering the outside of a wall with foam is that it moves the dew point farther from the framing. Adding 2 in. of foam to the outside of a house in a cold climate is often enough to move the dew point somewhere inside the foam, and therefore a place where interior humidity can’t get to. This means that cavity insulation won’t get wet and mold won’t grow inside your walls.

Download the full article on how thermal bridging works from Fine Homebuilding magazine.

Plus, browse articles at to learn a lot more about how insulation works and why it matters:

Insulation Overview

Insulating Roofs, Walls, and Floors

Insulation Choices