Thermal bridges are the weak links in a building envelope. They form wherever a high-conductivity material penetrates or bypasses the insulation layer, creating a fast lane for heat to escape. Steel shelf angles bolted to concrete slabs, cantilevered balcony slabs extending through the wall plane, parapets acting as thermal fins above the roofline, metal studs conducting heat across the wall cavity, window frames connecting interior finishes to exterior cladding: each of these conditions short-circuits the thermal barrier you spent so much effort designing.

The consequences go beyond wasted energy. Thermal bridges create cold spots on interior surfaces where condensation collects, leading to mold growth, material degradation, and premature failure of finishes. On the exterior, temperature differentials can cause efflorescence on masonry or ice damming at roof edges.

For the PDD exam, you need to recognize these conditions in section details and apply the right mitigation strategy. Continuous insulation that wraps unbroken around the building is the single most effective approach, but each condition also demands specific detailing. Thermal break assemblies at shelf angles, structural thermal break connectors at balcony slabs, insulated parapet cavities, exterior insulation outboard of metal studs, and thermally broken window frames all address distinct weak points.

This topic sits squarely in Objective 1.5, which asks you to detail and resolve how multiple building systems intersect. Thermal bridging is where structure, enclosure, and insulation systems collide, and getting the details right protects occupant comfort, energy performance, and long-term durability.