Thermal bridging and cold spots: why the corner goes black first

A thermal bridge is a path where heat bypasses the insulation because a conductive material runs unbroken from inside to outside. Concrete slabs, steel studs, and aluminum frames conduct heat far better than the insulation around them, so wherever they cross the wall they act like a wick, pulling heat out and leaving the interior surface along that path cold. Cold interior surfaces are where room moisture condenses first.

A closet on an exterior corner stacks every disadvantage at once. Corners concentrate framing and thin out insulation, so the surface runs cold. Closet doors stay shut, so heated room air never warms it. Clothes and boxes block what little air movement exists. The result is the coldest, stillest painted surface in the suite, condensing moisture nightly and drying slowest, which is exactly the sustained damp that staining needs.

When a balcony is a cantilevered extension of the floor slab, the same piece of concrete runs from the heated living room out into the weather with no break. Concrete conducts heat well, so the slab drains warmth from the suite and sheds it outdoors along the balcony's whole area, like a cooling fin. The floor strip and wall around the balcony door run cold all winter, and condensation finds them.

Thermal imaging is the fast way: an infrared camera maps surface temperatures across a wall in seconds and paints the bridges as cold streaks. A surface thermometer does the same work point by point. Low-tech evidence works too: the corners that stain, the wall sections where dust prints ghost lines over studs, and the spots residents say feel cold to the touch are all findings, and they usually agree with the camera.

Substantially. Steel and concrete conduct heat far better than wood, so a steel stud or an exposed concrete element moves much more heat through the same wall area than a wood stud would. This is why older concrete towers, with their exposed slab edges, uninsulated columns, and metal frames, produce the strongest cold-spot patterns in the region, and why ghost lines print more sharply on steel-framed walls.

Partially, and with care. Interior insulation over a cold wall or slab edge warms the room-side surface, which reduces visible condensation. But it also makes the structure behind it run colder, and if moist room air can still reach that structure, moisture can accumulate where nobody sees it. Interior fixes need an air-sealing plan alongside the insulation, and on chronic problems the durable fix is on the outside of the structure.

A deliberate interruption of a conductive path with a low-conductivity material. In modern windows it is a plastic section separating the outer and inner halves of an aluminum frame. In new concrete construction, engineered break assemblies connect balcony slabs to floor slabs through an insulating joint while still carrying the structural load. The principle is the same at every scale: cut the conductive path so heat has to cross an insulating layer.

Because their era built the structure straight through the envelope. West End, Kerrisdale, and Metrotown towers from the 1960s and 1970s typically have exposed slab edges at every floor, cantilevered balconies with no break, minimal wall insulation, and aluminum frames without thermal breaks. Each detail is a bridge, and together they make the suite perimeter one continuous cold zone. The buildings are structurally sound; they simply predate the thermal detailing.

It resets the evidence and nothing else. The corner is cold because of the structure behind it, and the next winter of nightly condensation will restain the new paint on the old schedule. Repainting has a place after the cause is addressed, as the finishing step. As the whole response, it is the most commonly purchased non-fix in strata maintenance, repeated every few years while the underlying damp keeps working on the drywall.

It is the most complete fix available, because insulation outside the structure keeps the concrete and framing warm rather than fighting them from inside. Overcladding with continuous exterior insulation warms slab edges, columns, and studs all at once, and it typically happens during recladding or major envelope renewal when the building is already being reworked. Balconies are the stubborn exception: a cantilevered slab cannot be wrapped, only mitigated.

Sometimes. A perimeter room that never holds heat despite working heaters may be losing it through bridged details: slab edges, a balcony, corner framing, old frames. But heating balance, duct issues, and simple air leakage produce the same complaint. What distinguishes bridging is surface evidence: cold-to-the-touch spots, condensation, and staining in the classic locations. A thermal imaging pass during an envelope assessment sorts the causes quickly.