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A. Proctor Group launches new thermal bridging calculation service

A new calculation service to provide thermal bridging heat loss calculations has been launched by A. Proctor Group. It fits seamlessly alongside the company’s other high quality technical support services,

including dynamic moisture movement calculations using WUFI®.



Heat loss at thermal bridges – expressed as Psi values – cannot be assessed through the U-value calculations used for the main building fabric elements. The thermal bridging calculation service therefore

complements A. Proctor Group’s existing U-value calculator, which has proved popular with website members.


Psi values are entered into SAP and SBEM calculations as part of assessing whole-building energy efficiency. There is no ‘correct’ Psi value to achieve, or even mandated maximum values as there are for

U-values in national building regulations.


The issue for designers and specifiers who obtain Psi values, whether through A. Proctor Group’s calculator or another source, is not being completely sure whether the performance achieved will actually help to

deliver a healthy building.


With that in mind, the new thermal bridging calculation service goes a step further in providing A. Proctor Group customers with information to help them understand how a thermal bridging detail performs.

The output includes a surface temperature factor, or fRSI. Where the calculated Psi value gives a value for heat loss, the surface temperature factor indicates the internal surface temperature at the junction detail.


This surface factor helps predict the likelihood of condensation and mould growth occurring. In residential buildings, a thermal bridge needs to achieve an fRSI of 0.75 or greater to ensure condensation will not occur. This clearly defined target is much more helpful when helping designers to understand the performance of their details.


Calculating Psi values also helps in assessing what contribution the detail might make to internal comfort for the building’s occupants, such as when trying to meet the voluntary Passivhaus standard or low energy designs.


“The A. Proctor Group’s ethos is to help create healthy buildings for people to spend time in,” said Iain Fairnington, Technical Director. “We operate based on what we call HAMM principles – heat, air and moisture management. So, using our new thermal bridge to advise customers about condensation risk was the obvious extra step to take, over and above Psi values alone.”


Using the Psi value and, in particular, the fRSI calculated by the software, the specialist technical team at A. Proctor Group can then advise on appropriate solutions utilising our ultra-thin Spacetherm® insulation solutions as well as our extensive range of membranes, if required, to contribute to the overall building performance goals.


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