If you look at an insulated wood-frame wall with a thermal camera, you’ll see a pattern of vertical lines representing the studs. Studs are an example of a thermal bridge—a portion of a building assembly with a higher thermal conductivity than adjoining areas.
Thermal bridges increase heat transfer through the building envelope, driving up heating and cooling bills. One study estimates that thermal bridging accounts for 10-15% of U.S. residential energy use. In winter, thermal bridges also create cold spots where condensation—and mold growth—can occur.
There are three types of thermal bridges:
Clear-field thermal bridges are distributed throughout a surface like a wall, floor, or roof. The bridging elements include framing like studs, joists, rafters, top and bottom plates, and headers. As we’ll see below, the effects of clear-field bridging can be modeled as a reduction in the thermal resistance of the entire surface.
Linear thermal bridges include concrete slab balconies and masonry party walls extending through the thermal boundary. Linear bridges can occur in any building type but are especially significant in commercial and multifamily buildings. Heat transfer through linear bridges increases with length.
Point thermal bridges occur when a beam or pipe passes through the thermal boundary. Heat transfer through point bridges depends on the number and type of penetration.
In this article, I’ll focus on clear-field thermal bridges in wood-frame assemblies. After a quick review of the relationship between thermal resistance and heat transfer, I’ll discuss series and parallel pathways. Understanding these pathways will allow us to calculate the effects of thermal bridging on overall R-value. I’ll wrap up by discussing practical strategies to reduce clear-field thermal bridging.
Heat loss, R-value, and U-value
The rate of heat transfer through an opaque surface like a wall increases with its…
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