Conservation of fuel and power: Approved Document L, Volume 2 — Buildings other than 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 thermal 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. For windows in buildings similar to dwellings, calculated for a standard window 1.23m (±25%) wide × 1.48m (–25%) high and the actual configuration of the window. c. For windows in buildings similar to dwellings, calculated for a standard window 1.23m (±25%) wide × 1.48m (–25%) high and one of the following standard configurations. Standard configurations should not be used for commercial windows. 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. NOTE: For domestic-type window construction, to be used in buildings similar to dwellings (see Table 4.1), the default value from the Standard Assessment Procedure (Table 6e) may be used if there are no test data or calculated performance values. 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 ≤ 3.6 m². ii. 2.00m (±25%) wide × 2.18m (±25%) high, for doors > 3.6 m². 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 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: These orientations should only be used when calculating U-values to check that they meet the limiting standards outlined in paragraphs 4.5 to 4.8 below. They should not be used in the energy calculations in Sections 1 and 2, where the U-value of each element is calculated based on the plane in which it is constructed or installed. 23 Building Regulations 2010 Approved Document L Volume 2, 2021 edition O N L I N E V E R S I O N