What is thermal bridging and how does exterior insulation mitigate it?

• A. Thermal bridging is heat loss through insulation gaps; exterior insulation does not affect it.
• B. Thermal bridging is heat transfer through windows; exterior insulation reduces glare.
• C. Thermal bridging is heat transfer through studs and framing; exterior insulation reduces it by adding continuous insulation.
• D. Thermal bridging is heat transfer through studs and framing; exterior insulation reduces it by adding continuous insulation.

Answer: (D)

Thermal bridging happens when heat moves easily through materials with high thermal conductivity in the building envelope, like studs and framing, creating a shortcut for heat to bypass the surrounding insulation. These studs stand out as paths of least resistance compared to the insulated wall cavity, so you get cold spots inside and more heat loss overall.

Exterior insulation adds a continuous layer of insulation on the outside of the structure, wrapping around the framing. This creates a more uniform resistance to heat flow and makes the insulation coverage around the studs continuous. Because the outer layer increases the amount of insulation that heat must pass through, the direct path through the studs is diminished, reducing the impact of thermal bridging.

So, thermal bridging is heat transfer through studs and framing, and exterior insulation mitigates it by adding continuous insulation around the outside of the wall.