Thermal bridging typically occurs at the junctions between plane building elements, e.g. at wall/roof and wall/floor junctions, and around openings, e.g. at window jambs, where the continuity of the insulation is interrupted.
Thermal bridging increases the heat loss and also the risk of condensation due to the lower localised internal surface temperatures.
The extra heat loss at a thermal bridging is measured by way of its linear thermal transmittance or Psi (Ψ) value in units of (W/mK).
Building Regulations require that heat loss calculations should include the effects of thermal bridges when calculating the Energy Performance Coefficient (EPC) and Maximum Permitted Energy Performance Coefficient (MPEPC) using DEAP.