This report guides the architect and specifier for calculating U-values by: -indicating the methods of calculation appropriate for different construction elements: roofs, walls, floors, basements, windows and doors -providing further information about using the methods -providing data relevant to typical UK constructions Particular guidance is given on thermal conductivity of materials, and on various issues commonly arising when calculating U-values and how they apply to different construction types. This 2006 edition of the guide is fully updated in line with Part L of the Building Regulations that came into effect in April 2006.