Thermal Bridging in Buildings

About this course.

A thermal bridge is a localised part of the building envelope where heat flows more easily than through the surrounding construction — in effect a short circuit through the insulation. You should care about it because these paths quietly waste energy, chill the inside surface of the building where they occur, and create the cold spots on which condensation, mould, staining and long-term durability problems develop. A wall may carry an impressive insulation value on paper yet perform poorly in reality, because heat is bypassing that insulation through studs, slab edges, balconies and junctions. Understanding where heat leaks, and why, is the first step to detailing it out.

Heat always moves from warmer to cooler, and through solid materials it moves by conduction. Different materials conduct at very different rates: metals such as steel are highly conductive; concrete and masonry are moderately conductive; timber is much less so; and bulk insulation is deliberately a very poor conductor. Insulation works by placing a layer of poor conductor across the whole envelope so that heat struggles to pass. A thermal bridge appears whenever a more conductive material penetrates or bypasses that insulating layer, giving heat an easier route around it. The familiar image is a metal fixing driven through insulation, but most real bridges are larger and structural — the edge of a concrete slab, a steel lintel, or the timber and steel members that make up a framed wall.