All new buildings have to meet minimum standards of energy efficiency. Achieving them makes extra demands on site practice and workmanship as well as on designers. Crucial to success is correct design and installation of thermal insulation. If there are gaps or weaknesses in the insulation, there will be cold spots in the building envelope, and these can lead to trouble. This Guide gives advice from BRE on how to build without gaps in insulation and how to avoid the problems caused by thermal bridges. 6 pages.