The 15m² and 30m² exemptions have different conditions, and neither automatically exempts every service connected to the building. They are also separate from planning permission. [1] [2] [3]
The two small-building tests
Under Schedule 2, Class 6:
- A detached building with a floor area not exceeding 15m², containing no sleeping accommodation, can qualify without the larger-building boundary or material restrictions.
- A detached single-storey building with a floor area not exceeding 30m², containing no sleeping accommodation, must either have no point less than 1m from the curtilage boundary or be constructed substantially of non-combustible material. [1]
The smaller exemption is not itself restricted to one storey. However, its area limit covers the aggregate floor area; a second floor does not provide another allowance. Planning rules can independently require a single-storey building. [4] [5]
Measure the right area and distance
LABC explains that the floor area is measured internally, adding all floors. This is different from assuming a catalogue's external footprint or advertised room size is the relevant figure. Ask for dimensions that make the calculation clear. [4]
For the larger exemption, consider the nearest part of the building, including projections such as gutters and fascias, when checking the boundary distance. Where non-combustible construction is needed, the specification must address the building substantially as a whole; a decorative finish is not an adequate description of its construction. [4]
Electrical and water connections are separate checks
Regulation 9 preserves Part P electrical requirements where the electricity is supplied from a source shared with, or located inside, a dwelling. Certain cold-water and hot-water-storage requirements also remain where the supply is shared with a non-exempt building. “The shell is exempt” therefore does not mean any cable or plumbing installation is acceptable. [2]
Have the installer identify the applicable requirements and notification route for each service. In particular, building work may be certified through an appropriate competent person scheme where the scheme covers that work; otherwise a building control application may be required. [6]
When the building does not qualify
Sleeping accommodation removes these Class 6 exemptions. Other reasons for needing approval include exceeding the relevant area, attaching the building to the house, or failing the applicable construction or boundary test. An exemption is a defined category, not an informal concession for inexpensive work. [3] [1]
Failure to qualify does not necessarily mean the building cannot be built. It means the design must follow the appropriate building-regulations approval and inspection process. Ask for the intended use, structure and services to be reviewed before ordering a standard kit. [4]
Keep the exemption assessment with the plans and installation certificates. If the building is subsequently altered or enlarged, check again: regulation 9 does not preserve exemption where the building would cease to be of the exempt kind after the work. [2]