What is a Thermal Bridge?

When considering insulation you may come across the terms thermal bridge or thermal break and not know exactly what they refer to..

So what is a thermal bridge?
Whenever there is a break in your insulation material generally for the purposes of a join, or opening, it acts as a thermal bridge, an unwanted path for heat loss.

Thus wherever a thermal bridge occurs it is a point where increased heat losses will occur, and something to be avoided if possible, which involves extra care during the design stages.

In a buildings these most often occur at door and window openings, as well as where different materials meet, floor to wall, wall to ceiling etc.  A thermal bridge is less of an issue in a poorly insulated home as there are already losses happening in other places where insulation is lacking.

Common thermal bridges are steel and timber studs, as framing materials they reduce the efficiency of the insulation. This loss is referred to as the 'framing factor' and can be reduced by placing insulation in series rather than in parallel.

Placing Materials In Parallel or in Series

Considering the different ways that materials are placed next to each other determines how they act thermally.

When you place materials in parallel – it means placing them sandwiched parallel to the direction of heat flow and acts to reduce the thermal resistance. (Air can find the path of least resistance and looks for a low R value material to do so)

  • Example - Metal window frame in a well insulated wall

Double glazed window shows materials in series. Plastic fitted in between the metal frame (shown in red) acts as a thermal break.

Placing materials in series (perpendicular/opposite to heat flow) increases the thermal resistance of the assembly, particularly by adding an air space (or other gas) in between.

  • Example - Double brick wall, with air cavity in between or double glazed window with argon.

Thermal Bridging and U Values

U values (sometimes called total R values) give a better indication of the performance of an ‘assembly’ as it takes into consideration the insulation material as well as other components, which in many cases will reduce the R value.

It is in a well insulated house, (what most of us are aiming for) that thermal bridges.

Selecting components that reduce thermal bridging will help to reduce losses as well as careful detailing at joints

Thermal Break
A thermal break is designed to reduce the flow of thermal energy (thus reduce the impact of a thermal bridge) by inserting an element of low thermal conductivity.

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