The short answer
A detached garden room is normally exempt from building regulations if it is small and nobody sleeps in it. Size, sleeping space and distance from the boundary decide it. Electrics are a separate rule and apply to almost every garden room.
The 15 m² and 30 m² rules
- Under 15 m² floor area. Building regulations do not normally apply, as long as nobody sleeps in it.
- 15 m² to 30 m². Building regulations do not normally apply, as long as nobody sleeps in it and it is either at least 1 m from every boundary or built mostly of non-combustible materials.
- Over 30 m². Outside these exemptions, so building regulations approval is normally needed.
- Any size with sleeping space. The exemptions do not apply once a room has sleeping accommodation.
St Albans council describes the 15 m² limit as internal floor area. Ask your builder to state the internal size on the quote.
So a garden office, garden gym or garden studio under 15 m² with no bed normally needs no approval. Up to 30 m², keeping it at least 1 m from every boundary normally does the same.
Sleeping space changes everything
The exemptions only apply to a building with no sleeping accommodation. Once a room has a bed for regular use, building regulations apply at any size.
That is why a garden annexe costs more and takes longer. It also usually needs planning permission. See our garden annexe rules.
Electrics: Part P
Part P covers electrical safety in homes in England. The Planning Portal lists which jobs must be notified:
- A new consumer unit (fuse box) is notifiable.
- A complete new circuit is notifiable. A garden room fed from the house usually needs one; your electrician confirms this for your build.
- Adding to an existing circuit is only notifiable in special locations. In England these are the spaces around baths and showers.
- A registered electrician can self-certify. Otherwise building control or a registered third-party certifier must be told before work starts.
Ask for the electrical certificate when the job is done. Keep it with your house papers.
If building regulations do apply
The room must be built to the standards in the regulations. A building control body checks the work. That is your council or a registered building control approver. Ask each builder who arranges this and whether the fee is in the quote.
Garden rooms near you
The rules are national, but builders who work locally deal with the same councils every week. We cover towns such as Hemel Hempstead, Harpenden, Kings Langley, Chesham and Beaconsfield.
Planning is a separate question. Read garden room planning permission.
Let a local builder check your plan
Builders we match you with tell you at the free site visit whether building regulations apply. Up to 3 quote.