Key facts at a glance
- Outbuildings fall under Class E Permitted Development if incidental to the house
- Max height 2.5m within 2m of a boundary, 4m otherwise (dual pitch)
- Total outbuilding coverage must not exceed 50% of garden area
- Habitable outbuildings (sleeping) always need planning + building regs
- Conservation areas: no outbuildings forward of the side elevation
- LDC recommended even for PD-compliant outbuildings (£129)
What counts as an outbuilding?
An outbuilding is any structure within the curtilage (garden) of a dwelling house that is not attached to the main house. This includes garden sheds, summer houses, greenhouses, garden rooms, home offices, studios, workshops, garages, swimming pool enclosures, and similar structures. Under the General Permitted Development Order (GPDO), these are covered by Class E of Schedule 2, Part 1, which allows buildings "incidental to the enjoyment of the dwelling house."
The critical word is "incidental." A garden office where you work from home is incidental -- it supports your use of the house. A garden building that you rent out to a third party, use as a separate dwelling, or use as a commercial business premises open to customers is not incidental. The distinction determines whether you need planning permission.
In London, where garden sizes are often modest and properties are close together, the PD rules for outbuildings matter enormously. Getting the dimensions or use wrong can result in enforcement action and an order to demolish the structure.
Permitted Development rules for outbuildings
Class E of the GPDO permits the erection of outbuildings without planning permission, subject to all of the following conditions:
Height limits
- Within 2 metres of any boundary: maximum eaves and ridge height of 2.5 metres
- More than 2 metres from any boundary, dual-pitched roof: maximum ridge height of 4 metres
- More than 2 metres from any boundary, other roof types: maximum height of 3 metres
- No upper-floor windows or openings
Coverage limit
The total area of ground covered by all outbuildings and extensions (excluding the original house) must not exceed 50% of the total area of the curtilage. This is cumulative -- if you already have a shed and a garage, any new garden room adds to the total. In small London gardens, this 50% rule is often the limiting factor.
Position restrictions
- The outbuilding must not be forward of the principal elevation (i.e., not in the front garden)
- In conservation areas, Areas of Outstanding Natural Beauty, and World Heritage Sites, outbuildings must not be positioned forward of the side elevation either, and the total ground coverage by outbuildings to the side of the house must not exceed 10 sqm
Use restrictions
- The building must be for a purpose incidental to the enjoyment of the dwelling house
- It must not contain sleeping accommodation (unless planning permission has been obtained)
- It must be single storey -- no mezzanines, galleries, or upper floors
If any one of these conditions is not met, the outbuilding is not Permitted Development and you need planning permission. There is no partial compliance -- all conditions must be met simultaneously.
When you need planning permission
Planning permission is required for an outbuilding in the following circumstances:
- The outbuilding exceeds PD height or coverage limits
- The outbuilding is to be used for sleeping accommodation (a granny annexe, guest bedroom, or rental unit)
- The outbuilding is for a commercial use open to the public (e.g., a therapy room, hairdressing salon, commercial kitchen)
- Your property is a flat or maisonette (no PD rights for outbuildings)
- Your property is a listed building (listed building consent required for any new structure in the curtilage)
- Your PD rights have been removed by an Article 4 Direction or a condition on a previous planning permission
- In a conservation area, the outbuilding is forward of the side elevation or exceeds 10 sqm to the side
The planning application for an outbuilding is a standard householder application (£258 council fee). The determination period is 8 weeks.
Home offices and garden rooms
The rise of remote working has made garden offices one of the most popular outbuilding projects in London. A purpose-built, insulated garden office with heating, electrics, and broadband is a significant investment -- but it can also add substantial value to your property and dramatically improve your work-life balance.
From a planning perspective, a home office used by the occupant of the house is incidental use and falls under PD (subject to the size and height limits). You do not need planning permission as long as:
- You work from the garden office yourself (or members of your household do)
- No clients or customers visit the premises
- No employees other than household members work there
- No goods are stored or dispatched from the premises
If your home business involves regular client visits, external employees, or commercial-scale activity, this may constitute a material change of use and require planning permission. The test is whether the use would be noticeable to a neighbour -- if it generates traffic, noise, or activity that changes the character of the garden, it is likely to require planning consent.
Building Regulations for garden offices
Most garden offices under 15 sqm are exempt from Building Regulations entirely. Between 15 sqm and 30 sqm, the structure is exempt if it is at least 1 metre from any boundary or built from non-combustible materials. Over 30 sqm, or if the building contains sleeping accommodation, a full Building Regulations application is required.
Regardless of the formal exemption, we recommend that all garden offices have:
- Electrical installation by a Part P registered electrician with a certificate
- Adequate insulation (100mm+ in walls, 150mm+ in roof) for year-round use
- Proper ventilation and heating
- A separate sub-main from the house consumer unit
Habitable outbuildings: granny annexes and garden flats
Using an outbuilding as a bedroom, guest suite, or self-contained dwelling always requires planning permission, because sleeping accommodation is not incidental to the enjoyment of the house under the GPDO. Additionally, the structure must comply with full Building Regulations:
- Part A (structure): Foundations, walls, and roof must be structurally adequate
- Part B (fire safety): Fire detection, escape routes, and fire resistance appropriate to the use
- Part C (moisture): Damp-proof course, insulation, and ventilation
- Part E (sound): If the outbuilding shares a boundary wall or is very close to a neighbour
- Part L (energy): Full thermal performance standards including U-values for walls, floor, roof, and glazing
- Part M (access): Level access and adequate circulation
- Part P (electrics): Full electrical installation by a competent person
If the outbuilding is a self-contained unit with its own kitchen and bathroom, the council may treat it as a new dwelling, which triggers CIL and potentially affordable housing contributions. If it is ancillary to the main house (e.g., a bedroom for an elderly relative with no separate kitchen), it is more likely to be approved as an ancillary residential annexe with a condition tying its use to the main house.
Costs for garden outbuildings in London
Typical garden outbuilding costs
If your outbuilding falls within PD limits, we strongly recommend a Lawful Development Certificate (£129). This provides formal legal confirmation that your outbuilding is lawful, which protects you against future enforcement action and is invaluable when selling the property. We prepare the LDC drawings and application as part of our service. Get a free quote.
Frequently asked questions
Do I need planning permission for a garden room in London?
If the garden room is incidental to the house (home office, gym, studio) and meets all Class E PD limits -- max 2.5m high within 2m of a boundary, not exceeding 50% garden coverage, single storey, not forward of the principal elevation -- then no planning permission is needed. In conservation areas, listed buildings, or where Article 4 Directions apply, planning permission is required. We recommend a Lawful Development Certificate (£129) for certainty. See our planning service.
Can I sleep in a garden outbuilding in London?
Using an outbuilding for sleeping takes it outside PD because it is no longer incidental to the house. You need planning permission and the structure must comply with Building Regulations for fire safety, energy, and structure. Some boroughs actively enforce against unauthorised sleeping in outbuildings. We prepare the planning and building regulations drawings for habitable outbuildings. See our building regs service.
What is the maximum size outbuilding I can build without planning permission?
There is no single maximum floor area under PD, but total outbuilding coverage cannot exceed 50% of the garden. Height limits are 2.5m within 2m of a boundary and 4m otherwise for a dual-pitched roof (3m for other roof types). The building must be single storey and incidental to the house. In practice, London gardens often limit you to 15-25 sqm before hitting the 50% threshold.
Do outbuildings need Building Regulations approval?
Non-habitable outbuildings under 15 sqm are exempt. Between 15-30 sqm, they are exempt if 1m+ from any boundary or non-combustible. Over 30 sqm or any sleeping accommodation requires full Building Regulations. Electrics must always be done by a Part P registered electrician regardless of size.
How much does a garden office cost in London?
A purpose-built insulated garden office in London costs £15,000-£40,000+ depending on size, specification, and finishes. A basic 3m x 4m timber-frame structure starts around £15,000. If planning permission is needed, add our drawing fees from £840 plus the £258 council fee. If PD applies, an LDC is just £129. Get a free quote.