Conservation of fuel and power: Approved Document L, Volume 2 — Buildings other than dwellings

O N L I N E V E RRS I2O3N(2), L1(a) 10.5 If a window, pedestrian door or rooflight is enlarged or a new one created, either of the following should be met. a. The area of windows, roof windows, rooflights and pedestrian doors should not exceed the relevant percentage from Table 10.1. b. If the area of windows, roof windows, rooflights and pedestrian doors exceeds the relevant percentage from Table 10.1, compensating measures should be taken to improve the energy efficiency of the building. Extension of buildings other than dwellings 10.6 Constructing an extension in buildings with a total useful floor area greater than 1000m2 triggers the requirement for consequential improvements. Section 12 should be followed. 10.7 An extension should be regarded as a new building, and guidance in Sections 1 to 9 should be followed, if the proposed extension has a total useful floor area that is both of the following. a. Greater than 100m2. b. Greater than 25% of the total useful floor area of the existing building. If the proposed extension does not meet criteria (a) or (b) above, the guidance in paragraphs 10.8 to 10.11 should be met. 10.8 When a building is extended, any fixed building services or on-site electricity generation that are provided or extended should comply with the guidance in Sections 5 and 6. 10.9 When a building is extended, elements should satisfy all of the following. a. New thermal elements should meet the standards in Table 4.1. b. Replacement thermal elements should meet the standards in Table 4.1. c. New windows, roof windows, rooflights and doors (controlled fittings) should meet the standards in Table 4.1. d. Existing fabric elements that will become thermal elements should meet the limiting standards in Table 4.2 by following the guidance in paragraphs 11.2 to 11.4. In addition, the area of openings in the extension should not exceed that given in Table 10.1, if either of the following areas are greater than that of the existing building. a. Window and pedestrian doors as a percentage of exposed wall. b. Rooflights as a percentage of area of roof. 71 Building Regulations 2010 Approved Document L Volume 2, 2021 edition O N L I N E V E R S I O N