Thermal Bridging
Heat shortcuts through structural elements that bypass the insulation.
Quick Answer
Thermal bridging is heat flowing through a more conductive material, such as steel studs, concrete slab edges, or metal fasteners, that interrupts or bypasses insulation. It lowers the real thermal performance of a wall or roof and can cause condensation. Designers reduce it with continuous insulation, thermal breaks, and careful detailing.
The Full Picture
Insulation only helps where it is continuous. Wherever a conductive element passes through or around it, such as framing members, balcony slabs, shelf angles, or metal clips, heat takes the easier path. These shortcuts are thermal bridges, and they can cut an assembly's effective insulation value well below the nominal value printed on the insulation product.
Bridging occurs at two scales. Repeating bridges, like studs and fasteners, are spread across a whole wall and are usually accounted for in assembly U-factors. Linear and point bridges occur at details such as slab edges, parapets, window frames, and connections where structure penetrates the envelope. These are often significant and historically ignored in simple calculations.
Consequences include higher energy use, cold interior surfaces, and condensation or mold where warm, moist air meets those cold spots. Steel is far more conductive than wood, so steel-stud walls and metal cladding supports are frequent concerns.
Common strategies include continuous exterior insulation, thermal breaks at balconies and window frames, low-conductivity clips and standoffs, and moving structure inside the insulated envelope. Energy codes such as ASHRAE 90.1 and the IECC increasingly address bridging directly through continuous insulation requirements, and detailed thermal modeling can quantify the remaining linear losses.
Real Examples
Common Misconceptions
People assume: The R-value on the insulation is the wall's R-value.
Actually: Framing, fasteners, and details reduce the effective R-value of the full assembly. The nominal value applies only to the insulation itself.
People assume: Thermal bridging only affects energy bills.
Actually: It also creates cold surfaces that can cause condensation, staining, and mold, and it affects occupant comfort.
Frequently Asked Questions
What is an example of a thermal bridge?
A steel stud passing through wall insulation, a concrete balcony slab extending through the wall, or a metal fastener through foam board are all common thermal bridges.
What is a thermal break?
A low-conductivity material placed in a conductive element, such as a plastic strip in a window frame or an insulating layer at a balcony connection, to interrupt heat flow.
How is thermal bridging reduced?
By using continuous insulation, thermal break products, low-conductivity attachments, simpler building forms, and by keeping structure inside the insulation layer.
Do energy codes address thermal bridging?
Yes. Codes such as the IECC and ASHRAE 90.1 set continuous insulation and assembly U-factor requirements that account for framing, which indirectly limits bridging.