Building Science
Thermal Bridge
A path through an assembly that conducts heat more readily than its surroundings, such as a steel stud or a cantilevered slab. It lowers whole-assembly performance and creates cold interior surfaces.
In more detail
A thermal bridge is a path through an assembly that conducts heat more readily than the material around it. Wood studs, steel framing, concrete slab edges, cantilevered balconies, window frames and structural fasteners through exterior insulation are all bridges of different severity — steel and concrete far worse than wood.
Bridges do two things. They lower whole-assembly performance, which is why a U-factor calculated with framing included falls short of what the cavity R-value would suggest. And they cool interior surfaces locally, which is a comfort issue and a moisture one: a surface below the dew point of indoor air collects condensation. That is why bridging often shows up as mold at a slab edge or dark lines on a ceiling tracking the joists.
Reducing them is geometric. Continuous exterior insulation covers framing bridges. Thermal breaks interrupt concrete and steel paths. Advanced framing reduces the amount of wood. Linear bridges are quantified as psi-values in W/(m·K) and point bridges as chi-values, both modeled rather than measured on site.
Why it matters
Thermal bridging explains the gap between the performance a house was specified for and the performance it delivers, and it explains complaints that insulation levels cannot — a cold corner, a floor that stays cool above a cantilever, condensation along one specific line on a ceiling. The corrections are almost entirely structural, which means they are drawn before construction or lived with afterward.
The common misunderstanding
That a bridge is only an efficiency problem. The surface temperature effect is usually what gets noticed: local cooling drives condensation and mold in a house whose average humidity is entirely reasonable. Bridges also concentrate the effect, so a small area of high conductance can cool a much larger area of adjacent surface.
Related terms
On Compound
Where this term does real work — and where the decisions get made.
Sources
Last reviewed July 2026 by Compound Editorial. Definitions are educational and not project-specific engineering or medical advice.