Susceptible materials are damaged by a combination of low temperature and high moisture contents. Cycles of wetting and freezing are more damaging than prolonged cold-dry conditions. Roof coverings can be damaged by "ground" frosts. Specification and quality control can influence performance as well as the level of building maintenance. Climate, constructional features, location in the building, frost susceptibility and quality control can all influence the risk of frost damage. This Guide gives advice on diagnosing frost damage and its likely course, and method of repair. Advice is given on the choice of whether to replace or repair, to help surveyors and contractors decide on appropriate action. Part 1 covers roofing, and Part 2 covers walls.