This document is intended for use by the building design team, building envelope designers and building inspectors. It allows the early estimation of building envelope U-values, details the information required in a specification, and describes methods for showing compliance of the final building envelope design with the requirements of Parts L-2A and L-2B of the Building Regulations.

The appendices show how detailed calculations should be undertaken to establish component U-values and the properties of the associated thermal bridges, and how these should be incorporated into a detailed calculation of the equivalent U-value of a zone of the building envelope.

Finally the document shows how the equivalent U-values of a zone of building envelope may be used as an input into software that models building energy use.