Technical Booklet F2 Conservation of Fuel and Power in Buildings Other Than Dwellings·Page 58·3.60
U-value calculation methods
U-values must be calculated using BRE Report BR 443 conventions based on whole unit performance. For windows, the U-value can be based on standard sizes from BS EN 14351-1, BR 443 standard configuration, or the actual unit size.
U-values should be calculated using the methods and conventions given in BRE Report BR 443 Conventions for U-value calculations, and should be based on the whole unit (e.g. in the case of a window, the combined performance of the glazing and frame). The U-value of windows can be taken as the value for – (a) the smaller of the two standard windows defined in BS EN 14351-1; (b) the standard configuration given in BR 443; or (c) the specific size and configuration of the actual unit. For domestic type construction, SAP 2009 Table 6e gives values for different window configurations that may be used in the absence of test data or calculated values.
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