What is thermal bridging in a house?
Thermal bridging is heat flowing around or through insulation by way of a more conductive material, such as wood studs, steel, concrete or window frames. It lowers the effective R-value of a wall, can leave cold spots that attract condensation, and is reduced with continuous insulation and thermal breaks.
What is a thermal bridge?
Insulation works because it resists heat flow, but a building is not one uniform layer. Wherever a more conductive material crosses the insulation, heat takes that path. The stud in a wall, a concrete balcony slab that runs from inside to outside and a metal window spacer are typical examples. Because heat flows like water along the easiest route, a small area with low resistance can carry a large share of the loss.
Where do thermal bridges occur in houses?
- Framing. Studs, plates and headers, which make up a sizeable share of a wall's area.
- Rim joists and floor edges. Where floors, walls and foundation meet.
- Window and door openings. Frames and the gaps around them, see high performance glazing for spacers and frames.
- Balconies, parapets and slab edges. Especially concrete or steel that pierces the envelope.
- Roof junctions. Eaves, and the places where wall and ceiling insulation fail to connect.
A thermal camera on a cold day makes them visible as stripes and patches on walls and ceilings.
How much does framing reduce a wall's R-value?
A small calculation helps. Assume a 2x6 wall with insulation of about R-20 in the cavity, wood studs at roughly R-7 across the same depth, and framing taking up about 23% of the wall area. Heat flow adds up in parallel: 0.77 of the area at R-20 and 0.23 at R-7 gives an overall figure near R-14. The label says R-20 but the wall behaves like R-14. The numbers are rough, but they show why the nominal value of cavity insulation overstates performance and why codes and energy tools use effective values. Our R-value guide explains how targets are set.
What are the effects of thermal bridging?
The first effect is higher heating demand. The second is comfort: the inside surface at a bridge is colder than the rest, so you feel a chill near the wall. The third is moisture. Warm, humid indoor air that meets a cold surface can condense and lead to mould or staining, often in corners and along the floor edge. The same physics produces the fog on cold glass discussed in condensation on windows in winter.
How do you reduce thermal bridging?
The most effective fix is continuous insulation, a layer that runs unbroken across the framing, usually on the outside. That is the idea behind the exterior wall insulation retrofit. Builders also use advanced framing, which reduces the amount of wood, double-stud or staggered-stud walls, insulated headers, thermal breaks in balcony and slab connections and insulated window installation details. Passive House designs set strict limits on bridges, as described in the passive house guide, and R-2000 homes treat the envelope as a system, see the R-2000 explainer. In existing houses, air sealing and insulating at the rim joist and attic edges give the best return, followed by exterior work when re-cladding.
Quick answers
Is thermal bridging the same as air leakage?
No. Thermal bridging is heat conducted through solid materials, while air leakage is heat carried by moving air. Both reduce performance and both need attention.
Does spray foam eliminate thermal bridging?
Not by itself. It fills the cavity but studs still conduct heat, so continuous insulation on the outside or inside is needed to cover the framing.
Can I see thermal bridges in my house?
A thermal camera used on a cold day shows them as cold lines and patches. An energy adviser may use one during an audit.