This Guide highlights a system of roof insulation where the insulation material is laid between and over inclined rafters: it is sometimes referred to as sarking insulation. Sarking insulation provides an effective solution to satisfying the thermal requirements of building regulations. It allows complex roofs to be more effectively insulated with a reduced risk of thermal bridging and condensation problems as the roofing timbers are kept at or near internal environmental conditions. This Guide provides advice on specifying sarking insulation and on avoiding the associated technical risks. 8 pages.