Thermal Bridging: The Sneaky Energy Thief in Your Walls
Estimated reading time: ~5 minutes
Energy codes and insulation are hot topics in construction, but there’s a lesser‑known culprit that steals heat (or cool air) from buildings: thermal bridging. A thermal bridge occurs where a conductive material, like steel, forms a continuous path through the insulation. It’s like giving heat an express lane through your wall. While many tradespeople know the term, its impact on energy bills and building durability isn’t discussed nearly enough.
What is thermal bridging?
A building’s envelope separates conditioned interior space from the unconditioned outside. It consists of multiple layers — sheathing, insulation, air barrier, cladding. Any part of this envelope that is more thermally conductive than its surroundings becomes a bridge. For example, using metal screws with metal sub‑framing can create a passageway that allows cold energy to travel from the exterior through connected metal components. When that cold meets warm interior air, condensation can form. This condensation can remain hidden yet cause mould, corrosion and decay.
Common thermal bridges
Points where the ground floor meets an external wall
Junctions where an external wall meets the roof
Around windows and doors (lintels and sills)
Balconies and cantilevered structures
Use of metal studs instead of wood
Penetrations for pipes and anchors
When heat flows through these paths, your HVAC system works harder, raising energy costs and carbon emissions. Surface temperatures near thermal bridges can drop below the dew point, encouraging condensation and mould growth, which undermines occupant health.
Real‑world consequences
Thermal bridges can reduce the effectiveness of insulation, increase heating and cooling loads and shorten the life of a building. A 2025 article from engineering consultants notes that thermal bridging is significant enough that UK building regulations (Part L) require designers to calculate Psi values for junctions in their Standard Assessment Procedure (SAP) and Simplified Building Energy Model (SBEM) calculations. Accredited Construction Details (ACDs) provide standardised designs to minimise heat loss at junctions, but these details must be followed meticulously to get credit.
Some manufacturers market thermally broken sub‑framing systems that provide structural support while interrupting heat flow. For instance, a technical article by Advanced Architectural Products explains that using a metal screw with metal sub‑framing can create a direct thermal bridge. Their GreenGirt composite metal hybrid (CMH) Z‑girt uses fiber‑reinforced polymer to break the path of conductive metals, maintaining structural strength while providing a thermal break. Systems like GreenGirt CMH® claim to eliminate thermal bridging, increase building envelope effectiveness and reduce energy and maintenance cost.
How to combat thermal bridging
Use continuous insulation outside of studs to cover framing members. This ensures there is no direct path for heat to bypass insulation.
Choose thermally broken connectors such as thermally insulated balcony connectors, composite Z‑girts or plastic fasteners. These materials interrupt the conductive path.
Detail junctions carefully. Follow accredited construction details or design custom details to maintain insulation at corners and transitions.
Consider warm‑edge spacers in windows to reduce thermal bridging at glazing.
Use modelling tools to calculate Psi values at junctions and evaluate the benefits of different assemblies.
As builders, we like to think our work is rock‑solid, but heat is the ultimate escape artist. Don’t let your wall become a giant leaky pipe; plan for thermal breaks, inspect the details and make sure your clients aren’t heating the neighbourhood. And the next time a buddy complains about his winter heating bill, you can tell him it’s because he left a “bridge” open.
