Technical Booklet F1 Conservation of Fuel and Power in Dwellings·Page 7·Regulation 38(3)
Exclusions from Regulation 40 for extensions
Dwelling extensions and small or proportionate extensions to other buildings do not need to comply with Regulation 40.
Regulation 40 shall not apply to—(a) the extension of a dwelling; and (b) the extension of a building other than a dwelling, unless the extension has a total useful floor area that is both—(i) greater than 100 m2; and (ii) greater than 25% of the total useful floor area of the existing building.
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