A garden room, home office or gym can often be built without a planning application if it serves an incidental household purpose and meets all the Class E permitted-development rules. A manufacturer's description such as “planning-free” is not a substitute for checking the actual site and intended use. [1] [2]
The principal size and position limits
For the ordinary Class E route, the building must be single storey and meet these limits:
- Eaves must not exceed 2.5m.
- Overall height must not exceed 4m with a dual-pitched roof, or 3m with another roof form.
- If any part is within 2m of a boundary of the house's curtilage, overall height must not exceed 2.5m.
- It cannot stand forward of a wall forming the original house's principal elevation.
- Buildings and other additions must not cover more than 50% of the land around the original house. [2]
The “original house” is the house as first built, or as it stood on 1 July 1948 if older. Later extensions and existing outbuildings therefore need to be included in the assessment; starting with today's remaining lawn can give the wrong result. [3]
These are cumulative tests, not alternative allowances. For example, a proposed roof might satisfy the general pitched-roof height limit but fail the lower boundary limit. Record both the roof form and the nearest boundary distance on the drawings. [2]
Check the property, not just the product
Householder rights do not apply to flats or maisonettes. A flat with its own garden is still a flat. Conditions on an earlier permission, Article 4 directions and certain permitted-development conversions can also prevent reliance on the ordinary rules. [1]
Class E is unavailable within the curtilage of a listed building. Conservation areas have additional siting restrictions, particularly beside the house; designation is not simply a blanket ban on every rear-garden outbuilding. A veranda, balcony or raised platform needs its own careful check. [1]
A home office is not automatically a business premises
A personal gym or home office may be an incidental domestic use. Southwark's household guidance identifies these as potential outbuilding uses, subject to the planning rules. [4]
An operation involving visiting customers, substantial deliveries or other business activity may raise a separate permission question. Explain how the room will actually be used, and check any landlord, mortgage and insurance requirements associated with homeworking. Do not describe a client-facing studio as a private office simply because the building is small. [5]
Keep planning and building control separate
The familiar 15m² and 30m² figures concern building-regulations exemptions, not a universal planning allowance. Sleeping accommodation also changes that assessment. A room may satisfy planning rules and still need building control approval. [6]
Before placing an order, assemble a site plan, elevations, intended-use description and schedule of existing buildings. A proposed Lawful Development Certificate can establish whether the specific proposal is lawful without a planning application; it is not a general approval for later changes of size or use. [7]