2. If a unit contains both living accommodation and space to be used for commercial purposes (e.g. as a workshop or office), the whole unit should be treated as a dwelling, as long as the commercial part can revert to domestic use. This can be the case if, for example:
a. there is direct access between the commercial space and the living accommodation; and
b. both are contained within the same thermal envelope; and
c. the living accommodation occupies a substantial proportion of the total area of the unit.
Note: Sub-paragraph c means that, for example, the presence of a small flat for a manager in a large non-domestic building does not result in the whole building being treated as a dwelling. Similarly, if a room is used as an office or utility space within a dwelling, that does not mean that the building should not be treated as a dwelling.
3. When constructing a dwelling as part of a larger building that contains other types of accommodation, sometimes called a mixed-use development, use this Approved Document L1A for guidance in relation to each individual dwelling. Approved Document L2A gives guidance relating to the non-dwelling parts of such buildings, such as heated common areas, and in the case of mixed-use developments, the commercial or retail space.
Material changes of use
4. The act of erecting a new dwelling is not a material change of use. Approved Document L1B applies where a dwelling is being created in an existing building as the result of a material change of use of all or part of the building.