Buildings with mixed residential and business use

Where a building contains living accommodation and also contains space to be used for professional, industrial or commercial purposes (e.g. a doctor's surgery, a workshop or office), the whole building should be treated as a dwelling if the business part could revert to domestic use. Consequently, it should be designed and constructed in accordance with the provisions in Technical Booklet F1. This would be the case where all of the following apply – (a) there is direct access between the living accommodation and the business part; (b) both are contained within the same thermal envelope; and (c) the living accommodation occupies the greater proportion of the total floor area of the building. Sub-paragraph (c) means that a small flat for a manager in a large non-domestic building would not mean the whole building should be treated as a dwelling. Similarly, the existence of a room used as an office or utility space within a dwelling would not mean that the building should not be treated as a dwelling.