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

O N L I N E V E R S I O N R23(2), L1(a) 10.6 The term controlled fitting refers to the entire unit of a window, roof window, rooflight or door, including the frame. Replacing glazing, or a window or door in its existing frame is not providing a controlled fitting. Such work does not need to meet the energy efficiency requirements. Extension of a dwelling 10.7 When a dwelling is extended, elements should satisfy all of the following. a. New thermal elements should meet the standards in Table 4.2 and paragraph 4.7. b. Replacement thermal elements should meet the standards in Table 4.2 and paragraph 4.8. c. New windows, roof windows, rooflights and doors should meet the standards in Table 4.2. d. The total area of windows, roof windows, rooflights and doors in extensions should not exceed the sum of the following. i. 25% of the floor area of the extension. ii. The total area of any windows and doors which no longer exist or are no longer exposed due to the extension. e. Existing fabric elements that will become thermal elements should meet the limiting standards in Table 4.3 by following the guidance in paragraphs 11.2 to 11.4. 10.8 When a dwelling 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 As an alternative approach to paragraph 10.7, the area-weighted U-value of all thermal elements in the extension should be shown to not exceed the area-weighted U-value of an extension of the same size and shape that complies with paragraph 10.7. The area-weighted U-value is given by the following expression. [(U × A) + (U × A ) + (U × A ) + …] 1 1 2 2 3 3 (A + A + A + …) 1 2 3 Where: U = the U-value of element type 1 1 A = the area of element type 1 1 and so on. 10.10 As an alternative approach to paragraphs 10.7 or 10.9, the Standard Assessment Procedure may be used to show that the dwelling primary energy rate, the dwelling emission rate and the dwelling fabric energy efficiency rate for the dwelling and proposed extension do not exceed those for the dwelling plus a notional extension. The notional extension should be the same size and shape as the proposed extension and comply with paragraph 10.7. The openings in the notional extension should conform with paragraph 10.7d, with the door area set as equal to the door area of the proposed extension and the remainder of the openings being classified as windows. NOTE: Where the performance of elements of the existing dwelling is unknown, data in the Standard Assessment Procedure Appendix S should be used to estimate the performance. 62 Approved Document L Volume 1, 2021 edition Building Regulations 2010 O N L I N E V E R S I O N