BRE - Roof loads due to local drifting of snow

Organization: BRE
Publication Date: 1 August 1999

British Standard BS 6399-3:1988, presented snow loading data independently of other imposed roof loads, and a more sophisticated approach than the uniform imposed roof load allowance previously used in design. The complexity of the design method and the magnitude of local drift loads for some cases, was criticised. Following a review of some areas of difficulty, BS 6399-3 was amended.The main changes relate to determining load shape coefficients for local drifting of snow, and using the snow load statistical factor to produce estimates of loads with probabilities of exceedance different from 0.02. This Digest presents background information and design requirements for local snow drift loads on roofs in accord with the amended British Standard. It is aimed at architects, structural engineers, contractors, and manufacturers and suppliers of roofing systems. Digest 332 is now withdrawn.