D3 Construction in Extreme Climates

Topic

A thermal bridge is a point in the building envelope where insulation is interrupted or compromised—such as a corner, the junction between a floor slab and the façade, or the perimeter of a window. Consequently, it acts as a preferential pathway for heat loss, being far more permeable than the rest of the enclosure, whose thermal resistance was already established by the heat transfer module. This additional leakage can be viewed as extra heat loss per linear meter of the thermal bridge, proportional to the temperature difference between the interior and exterior.

Beyond energy loss, a thermal bridge has a second, often more serious consequence: because it is a colder point than the rest of the enclosure, its interior surface temperature can drop low enough to promote surface condensation and, subsequently, mold growth. This revives the condensation risk previously described in the moisture and vapor module, but now localized at a specific point in the envelope rather than distributed across the entire wall. An indicator compares how close the interior surface temperature at that point is to the actual indoor temperature, relative to the total indoor-outdoor temperature difference; the closer this indicator is to the indoor temperature, the lower the risk of condensation at that exact spot.

In cold climates, where the temperature difference between the interior and exterior is significant for much of the year, this risk is exacerbated. Therefore, envelope design actively seeks to eliminate or minimize thermal bridges by ensuring insulation continuity at all construction junctions, rather than allowing the wall's thermal resistance to be interrupted at its edges.

Thus, this module—which begins by discussing insulation that is interrupted at a specific point in the envelope—concludes by demonstrating that this single weak point not only loses more heat than the rest of the wall but also concentrates the moisture risk that is otherwise more widely distributed and controlled across the rest of the enclosure.

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