Thermal Bridge Elimination

A thermal bridge is any element with higher thermal conductivity than the surrounding insulation that creates a continuous path through the building envelope. In a conventional 2×6 wood-framed wall insulated with fibreglass batts, the studs — spaced 400mm on center — occupy roughly 25% of the wall area. Softwood has a thermal resistance of approximately R-1.25 per inch, while the batt insulation provides R-3.5 per inch. The studs conduct heat at nearly three times the rate of the insulation they interrupt. When engineers calculate effective R-value rather than nominal R-value, that R-22 wall performs closer to R-15. The gap between what you think you built and what you actually built is the thermal bridge penalty.

The consequences extend beyond energy loss. The Passive House Institute in Darmstadt, Germany, has documented that thermal bridges cause localized surface temperature drops on interior finishes. When interior surface temperature falls below 12.6°C — the threshold for mold growth at typical indoor humidity — condensation and biological growth become inevitable. In cold climates, this happens not at dramatic failures but at mundane connections: the corner where two walls meet, the junction of wall and roof, the edge of a window frame, the steel lintel over a door. The Passive House standard requires that linear thermal transmittance (Ψ-value) at all junctions remain below 0.01 W/mK — effectively thermal-bridge-free construction. Buildings meeting this standard in climates as severe as Innsbruck, Austria (January mean: −1°C) have demonstrated heating demands below 15 kWh/m² annually.

Canadian practice is catching up. The BC Energy Step Code, in its higher performance tiers, requires thermal bridging calculations using software like THERM to model two-dimensional heat flow through assemblies. Natural Resources Canada's guidance on high-performance housing recommends continuous exterior insulation — rigid foam, mineral wool boards, or insulated sheathing — as the primary strategy to break thermal bridges. A 50mm layer of exterior mineral wool (R-8) wrapped continuously around the framing reduces the thermal bridge effect of studs by over 60%. The deep wall assemblies described in Pattern 46 achieve this through a different geometry: by separating the structural frame from the insulation plane entirely, using double-stud walls with a gap between, the thermal bridge is eliminated at its source. There is no conductive path because the studs do not touch.

At critical junctions — balconies, canopies, parapet connections — the thermal bridge problem becomes acute. A concrete balcony slab that penetrates the floor assembly creates a thermal fin radiating heat to the exterior. Schöck Isokorb and similar structural thermal break elements, developed in Germany and now available in North America, use a combination of stainless steel reinforcement and insulating material to maintain structural continuity while interrupting thermal continuity. These elements reduce heat loss at balcony connections by 80% or more.