BRE IP106 is the industry-recognized methodology in the UK for assessing the risk of surface condensation. It provides the mathematical framework for calculating temperature factors in various structural geometries. Compliance with this standard is often required to satisfy Part L Building Regulations and to prove that a design is "healthy" as well as energy-efficient.

While "Accredited Construction Details" (ACDs) or default values can be used in some SAP assessments, they are often conservative and penalize the building's energy rating. Bespoke fRsi and Psi-value calculations provide more accurate data, often revealing better performance than defaults and providing the only way to verify mold-risk protection in complex or non-standard junctions.

Mold thrives when the internal surface temperature at a junction (like a corner or window lintel) falls below a certain threshold, causing moisture in the air to condense. By modeling the junction, we ensure the fRsi exceeds the critical limit (typically 0.75 for dwellings). If the value is too low, we recommend structural changes—such as adding insulation "fins" or changing materials—to raise the surface temperature.

Ideally, these calculations should be performed during the technical design stage. Identifying a low fRsi value early allows architects to adjust the insulation layout before construction begins. Remedying a thermal bridge after the building is completed is significantly more expensive and often involves invasive retrofitting.