Calculating U-values for buildings with extension(s)

In line with CN β€˜Extensions to existing buildings and newly constructed thermal elements’, the performance of the baseline for new thermal elements should be based upon compliance with the appropriate local or national Building Regulations for new thermal elements.

When completing the Elemental level energy model, the existing building U-values for the thermal elements should be calculated as the area-weighted average of the relevant thermal element (e.g, external wall, roof, glazing or ground floor area), excluding any area that is removed to accommodate the extension, and that of the extension, built to meet the local minimum building performance standards.

The U-values for thermal elements of the refurbished building should be calculated as the area-weighted average of the relevant thermal element for refurbished building, including the extension.

This applies when assessing against the ‘Elemental level energy model’ option.