What Counts as an Outbuilding?

For permitted development purposes, an outbuilding is any structure in the garden that is incidental to the enjoyment of the dwelling house. This covers a wide range of structures including:

• Garden sheds and storage buildings
• Summerhouses and gazebos
• Garden rooms and home offices
• Greenhouses and potting sheds
• Swimming pool enclosures and pool houses
• Garages (detached, in certain circumstances)
• Sauna cabins and hot tub enclosures
• Workshops and hobby rooms

The phrase “incidental to the enjoyment of the dwelling” is key. A structure used as a separate residential unit — for example, if someone other than the household lives there permanently — would not be incidental and would need planning permission as a separate dwelling.

The Permitted Development Rules

Outbuildings fall under Class E of Schedule 2, Part 1 of the General Permitted Development Order (GPDO) 2015. This allows homeowners to build outbuildings within the curtilage of a house without making a planning application, as long as certain conditions are met.

Size and Height Limits

The maximum height of an outbuilding depends on its roof type and how close it is to a boundary:

There is no maximum footprint stated in the rules per se, but there is a maximum coverage rule (see below) that effectively limits how large your outbuilding can be.

Outbuildings must be single storey only. A mezzanine level or sleeping loft would likely be treated as a two-storey structure.

The 50% Garden Coverage Rule

This is one of the most important — and least understood — rules. The total area covered by all outbuildings and extensions must not exceed 50% of the total garden area.

This 50% is calculated based on the garden as it existed when the house was originally built (or as at 1 July 1948 for older properties). The original house footprint is excluded from the calculation — it’s just the garden area that matters.

The calculation includes:

• All existing outbuildings (sheds, garages, greenhouses)
• Extensions already built
• The new outbuilding you want to build
• Any other structures within the garden curtilage

So if your garden is 100m² and you already have a 10m² shed, you can add outbuildings up to a total of 50m² — meaning a further 40m² is available for the new structure (10 + 40 = 50m²).

Where Can It Go?

Outbuildings permitted under Class E must be within the curtilage of the dwelling house — this is essentially your garden and any land directly associated with the property.

There are restrictions on positioning:

• Outbuildings must not be in front of the principal elevation (the front wall of the house as it faces the highway)
• They can go in the rear garden or side garden
• On corner plots, the “side” may be treated as a front elevation if it faces a public highway — check with your council if unsure
• There is no minimum distance from the house itself (unlike extensions), though fire safety and building regulations may impose practical constraints

Can I Use It as Living Space?

This is where many people run into problems. Permitted development allows outbuildings that are incidental to the use of the main house. Using an outbuilding as a self-contained residential unit — either for rental income or for a family member to live in full-time — is not permitted development and would require planning permission as a change of use.

The tests councils use to determine whether use is “incidental” include:

• Does the structure have its own kitchen and bathroom (suggesting independent living)?
• Is it let out or occupied by someone not part of the main household?
• Does it have its own separate postal address?
• Is it connected to separate utility meters?

A garden room used by the household as a home office, hobby space, gym, or cinema room is fine. A “granny annexe” where someone lives full-time is a different matter and typically requires planning permission — although some councils may be flexible depending on the circumstances.

Home Offices and Garden Rooms

Garden offices and home studios are the most popular outbuilding type today. The good news is that these almost always qualify as permitted development, provided the structure stays within the size limits. The use (working from home) is clearly incidental to the dwelling house.

Practically speaking, most off-the-shelf garden rooms from specialist suppliers are designed to comply with PD rules. However, be aware that:

• Units over a certain size may require Building Regulations approval (see below)
• If you plan to use the structure commercially (client visits, employees working on-site), the planning position may be different
• Electricity, plumbing and heating connections require their own sign-offs under Building Regulations

When PD Doesn’t Apply

Permitted development rights for outbuildings do not apply in the following situations:

• Flats and maisonettes: Class E only applies to houses, not flats or converted buildings
• Listed buildings: Any works require listed building consent and usually planning permission
• National Parks, AONBs, conservation areas: Outbuildings permitted development is more restricted in designated areas — check with your local planning authority
• World Heritage Sites: As above
• Article 4 Directions: Some councils have removed PD rights for outbuildings
• Developer conditions: Some new build estates have planning conditions removing PD rights — check your title register

Building Regulations

Just because an outbuilding is permitted development doesn’t mean it’s exempt from Building Regulations. Here’s the rough breakdown:

• Under 15m² floor area: Exempt from Building Regs if not used for sleeping
• 15–30m² floor area: Exempt if it’s at least 1 metre from the boundary, made of non-combustible materials, and not used for sleeping
• Over 30m² floor area: Full Building Regulations approval required

Even in exempt cases, you’ll still need a registered electrician to sign off any electrical installation under Part P. And if you’re running water and drainage, plumbing work will need appropriate sign-off too.