This report represents an update of the BRE guide first produced in 1989 and extensively revised in 1994. The approach of these earlier editions, highlighting the link between risks, causes and solutions, has been retained. This updated edition contains a number of revisions resulting from developments in research, changes in materials, construction techniques and the building regulations. The guide has been prepared to support the building regulations for the conservation of fuel and power. The information in this guide represents the recommendations of BRE on good design and construction practice associated with thermal standards. It discusses the more important technical risks associated with meeting the requirements of the building regulations for thermal insulation. Technical risks are highlighted and these are followed by actions that could be taken to avoid the risk.