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

R23(2), LO1N(aL I)N E V E R S I O N Table 10.1 M aximum area of openings in the extension Building type Windows and pedestrian doors Rooflights as % of area of roof as % of exposed wall Residential buildings where people 30 20 temporarily or permanently reside Places of assembly, offices and shops 40 20 Industrial and storage buildings 15 20 NOTE: Vehicle access doors, display windows and similar glazing and smoke vents can be as large an area of wall or roof as required for the purpose. 10.10 As an alternative approach to paragraph 10.9, 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 10.9. This includes the opening area standards in Table 10.1. 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. 10.11 As an alternative approach to paragraphs 10.9 or 10.10, an approved calculation tool may be used to demonstrate that the building primary energy rate and the building emission rate for the building and proposed extension do not exceed those for the building plus a notional extension. The notional extension should be the same size and shape as the proposed extension and comply with paragraph 10.9. All calculations should include all consequential improvements that may apply. 72 Approved Document L Volume 2, 2021 edition Building Regulations 2010 O N L I N E V E R S I O N