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Cross-market term

Thermal bridge

A path through the envelope that conducts heat faster than the surfaces around it — usually where two elements meet, or where a structural member interrupts the insulation.
  • 4Markets
  • NoSame thing everywhere
  • 3Calculators

What it is called, by market

One concept, four markets. Where a name means something else locally, the card says so rather than leaving you to find out on site.

  • United Kingdom

    Same word, different thing

    thermal bridge

    also cold bridge, psi value, y-value, junction detail, accredited construction details

    PSI VALUE is a linear transmittance in W/m·K for a specific junction, summed over its length. It is a separate quantity from the U-value of the surfaces, added to them rather than included.

  • Australia

    Close, not identical

    thermal bridge

    also thermal bridging, steel framing correction, total R-value

    Addressed mainly through a correction applied to a framed wall's total R-value rather than a per-junction figure, so the arithmetic differs even where the concept matches.

  • United Statesyours

    Same word, different thing

    thermal bridging

    also continuous insulation, ci, framing factor, parallel path, clear field

    Usually handled by REQUIRING continuous insulation of a stated R-value rather than by calculating the bridge. CI is a prescription; a psi value is a measurement.

  • Canada

    Close, not identical

    thermal bridging

    also continuous insulation, effective R-value, linear transmittance, point transmittance

    EFFECTIVE R-VALUE is the assembly figure after bridging is deducted, and Canadian practice publishes catalogues of linear and point transmittances closer to the British approach.

The governing standard, by market

  • United Kingdom

    BR 497 / BRE IP 1/06

    Conventions for calculating linear thermal transmittance and temperature factors, and assessing the effects of thermal bridging at junctions.

  • United States

    ASHRAE 90.1 / ASHRAE 1365-RP

    Energy standard requirements including continuous insulation, and the research report giving linear and point transmittances for building envelope details.

Calculators for this

Each works in either measurement system, and the terminology on the page follows whichever market you have selected.

Thermal Bridging Effective R-Value Calculator →Continuous Insulation Thermal Bridging Calculator (Z-Furring) →Window Wall Area-Weighted U-Factor Calculator →

Frequently asked questions

Is a thermal bridge included in a wall's U-value?
The repeating ones are; the junctions are not, and that is the distinction that gets lost. A U-value is calculated for a REPEATING assembly, so bridges that recur at a regular spacing through it — the studs in a timber wall, the mortar joints in blockwork, the ties across a cavity — are already averaged into the figure. What is not in it is every place the assembly STOPS: where the wall meets the floor, the roof, a window reveal, a lintel, a balcony, a party wall. Those are one-off geometries, they are where insulation is most often interrupted, and in a well-insulated building they can account for a substantial share of the total fabric heat loss. British method adds them explicitly as a sum of psi-values times lengths. Anyone reading a U-value as the whole story is reading the easy part of the envelope and ignoring the part the site actually gets wrong.
Why do thermal bridges matter more as insulation improves?
Because the bridge does not improve with it, so its SHARE of the loss grows. Insulating a wall better reduces the heat going through the field of the wall, but the junction where the insulation is interrupted conducts at much the same rate it always did — its geometry has not changed. A poorly insulated building loses heat everywhere and the junctions are a rounding error; a well-insulated one loses heat mostly at the places the insulation stops. The consequence is that upgrading insulation without improving the junctions gives less than the arithmetic promises, and the gap widens the better the insulation gets. It is also why detailing takes over from specification as the envelope improves: choosing a thicker board is a purchase, and making the insulation line continuous around a lintel is a drawing and a site instruction.
What is the temperature factor, and why is it not about energy?
It is about MOULD, and it is the reason a thermal bridge can be a health problem rather than a bill. The temperature factor compares the temperature of the internal surface at the bridge against the difference between inside and outside, giving a number that says how cold that surface gets relative to the room. Energy loss is proportional to area and a small junction loses little, but the SURFACE there can be cold enough for the air against it to reach its dew point — and a surface that spends winter above roughly eighty percent relative humidity grows mould, well before it is cold enough to show condensation running down it. That is why guidance sets a minimum temperature factor for junctions independently of any energy target, why mould in a corner or behind a wardrobe on an external wall is a detailing symptom rather than a housekeeping one, and why a bridge that costs almost nothing in heat can still fail.