If the surface temperature factor (fRSi) is controlled incorrectly, thermal bridging is likely to result in condensation and mould growth problems.

Does WUFI or Therm do a good job of predicting where there is a potential for condensation and use the Frsi factor?

Architecture, Design & Innovation

.   Chris Willett, MD at Schöck Ltd, considers the issues involved

To identify areas where there is a risk of condensation and therefore mould growth in different design situations, a ‘surface temperature factor’ (fRsi) can be used. It allows surveys under any thermal conditions and compares the temperature drop across the building fabric, with the total temperature drop between the inside and outside air. The ratio is described in BRE IP1/06; a document cited in Building Regulations Approved Documents Part L1 and L2 and Section 6 in Scotland

It is a critical calculation, as the consequences of condensation and mould growth are likely to be more serious for building occupiers than any local heat loss. If low internal surface temperatures in the area of a thermal bridge are below the dew point of the air, condensation is almost certain to form.   This in turn is likely to…

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