Designers are often focussed on u-values; however one of the most important aspects of Passivhaus design is the elimination of thermal bridging at junctions. As the amount of heat lost through the plane elements reduces through improved u-values, so the amount lost through thermal bridges actually increases, as this is the path of least thermal resistance. For structural reasons, it can be challenging to eliminate thermal bridges entirely, but with careful detailing they can be minimised. Whilst not a certification requirement of Passivhaus, a detailed understanding of the impact of any changes to the construction on the magnitude of thermal bridges is vital when designing Passivhaus buildings.
The simplest and most cost effective way to achieve thermal bridge free design would be to externally insulate the building but this is not always possible due to planning restrictions.
BRE use three dimensional thermal bridge modelling software (TRISCO) to quantify psi (Ψ) values and surface temperatures.
BRE offer thermal bridge modelling as an additional service, modelling specific details to ensure compliance with the standard and working with the design team to develop new and improved details.