Topic

Thermal bridges

A thermal bridge is a spot where heat bypasses the insulation: a concrete balcony slab running straight through the wall, a steel beam, the studs in a frame wall, a window set disconnected from the insulation around it. On a cold day, a thermal camera shows them as bright stripes.

They waste energy, and the better the insulation, the larger their share: unaddressed, they can account for half the heat lost through a Passive House enclosure. They also make cold spots inside. Where a bridge pulls an interior surface toward the outdoor temperature, moisture collects, and mold can start, often in a corner behind furniture.

Passive House design removes them: keep the insulation's thickness unbroken at every junction, and don't let a more conductive material pass through it. Trace the insulation around a section without lifting the pencil; wherever the pencil lifts, there's a bridge. A junction whose extra heat loss stays under 0.006 Btu/(hr·ft·°F) (0.01 W/(m·K)) counts as thermal-bridge-free in PHI's energy model. An unavoidable bridge is calculated and counted. Every detail must keep its inside surface warm enough to stay free of mold, against a limit PHI sets by climate; the colder the climate, the stricter the limit.

In a retrofit, the existing structure often prevents this, so the aim is to minimize them.

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