Conservation of fuel and power: Approved Document L, Volume 1 — Dwellings

O N L I N E V E R S I O N L1(a) Section 4: Limiting heat gains and losses U-values 4.1 U-values should be assessed using the methods and conventions set out in the Building Research Establishment’s BR 443. U-values should be assessed for the whole fabric element (e.g. in the case of a window, the combined performance of the glazing and the frame). 4.2 The U-value of a window should be assessed using one of the following methods. a. Calculated using the actual size and configuration of the window. b. Calculated for a standard window 1.23m (±25%) wide × 1.48m (–25%) high and the actual configuration of the window. c. Calculated for a standard window 1.23m (±25%) wide × 1.48m (–25%) high and one of the following standard configurations. i. For a casement window, a central vertical divider with one opening light and one fixed light. ii. For a vertical sliding sash window, a central horizontal divider with two opening lights. iii. For a roof window, no divider. d. Measured using the hot-box method as set out in BS EN ISO 12567-1 for windows and BS EN ISO 12567-2 for roof windows. 4.3 The U-value of a door should be assessed using one of the following methods. a. Calculated using the actual size and configuration of the door. b. Calculated using one of the following standard sizes. i. 1.23m (±25%) wide × 2.18m (±25%) high, for doors ≤ 3.6m². ii. 2.00m (±25%) wide × 2.18m (±25%) high, for doors > 3.6m². NOTE: When a single U-value is calculated for a product range of doors, the configuration of the door chosen for the calculation should be the worst performing in the product range. c. Measured using the hot-box method as set out in BS EN ISO 12567-1. 4.4 Alternatively, for doors or windows, the default value from the Standard Assessment Procedure Table 6e can be used. 4.5 To correctly assess whether an element meets the limiting U-value, the U-value must be calculated for the element in the appropriate plane – either horizontal or vertical. For windows and roof windows, U-values should be calculated based on a vertical position. For rooflights, U-values should be calculated based on a horizontal position. If the data available for the element is in the incorrect plane, it should be adjusted according to the guidance in the Building Research Establishment’s BR 443. NOTE: This does not apply to Standard Assessment Procedure calculations, where the U-value of each element is calculated based on the plane in which it is constructed or installed. Limiting standards in new dwellings 4.6 Insulating fabric elements in new dwellings should meet the limiting standards in Table 4.1. Building Regulations 2010 Approved Document L Volume 1, 2021 edition 23 O N L I N E V E R S I O N