Framing - Thermally Broken Frames

A thermal break is a material of low thermal conductivity placed in an assembly to reduce or prevent the flow of thermal energy between conductive materials. Thermal breaks have traditionally been the focus of cold climates but are now deemed a good design practice in all climates where performance design is a consideration.

In the context of glazing systems, thermally broken refers to frame products with a low thermal conductivity material to avoid unwanted heat loss or gain and lower condensation risk. Market-dependent thermal breaks of PVC, neoprene rubber, polyurethane and polyester-reinforced nylon are used for improved thermal performance. A thermal break separating the external and internal framing elements is at least 5.3 mm thick. It can be up to 25 mm or more with the polyester-reinforced nylon varieties.

Classified by the U.S. National Fenestration Rating Council (ref: NFRC 100-2016), thermal breaks can be defined as:

‘Thermal break: a material of low thermal conductivity inserted between members of high conductivity to reduce heat transfer. Thermal barrier material conductivity shall be no more than 0.5 W/mK’.

Where an installed thermal break does not meet the above definition, particularly in reference to its depth and ability to separate external and internal framing components, it may be defined as thermally improved. In temperate climates, such thermal improvements provide good value reductions to heat transfer and are common in curtain wall systems.