Home Office Extensions in London: Planning, Cost and Design

A home office extension in London can be a single storey rear or side extension, or a first floor room over one. On a house, many need no planning application, but all must meet the building regulations. From extensions we priced in August 2026, new space at a high standard generally runs £2,400 to £2,800 per square metre, ex VAT, before fees and indicative.

A loft office or a garden office can be the better answer. Here is how the three compare.

Each route gives you a quiet room to work in, and the house usually decides:

• Home office extension: a room built as part of the house, which suits a house that is extending anyway.
• Loft office: a study within a loft conversion, which suits a house that needs a bedroom too and has height in the roof.
• Garden office: a detached single storey building, which suits a house with enough garden, used by the household only.

Our published cost guides price extensions and loft conversions, not garden offices, so the figures below cover those two routes.

Often not, on a house. Many single storey extensions are permitted development, allowed within set limits without a planning application. In England, as of September 2026:

• Rear extensions: up to 3 metres beyond the original rear wall of a terraced or semi detached house, or 4 metres for a detached house, and no more than 4 metres high. Prior approval, in which the council consults the neighbours, allows up to 6 or 8 metres.
• Side extensions: single storey, no more than 4 metres high, and no wider than half the width of the original house.

A first floor home office faces tighter limits:

• Depth: no more than 3 metres beyond the original rear wall, and at least 7 metres from the rear boundary.
• Eaves: no higher than 3 metres within 2 metres of any boundary, which a first floor cannot meet, so on most terraced and semi detached houses a two storey rear extension needs planning permission.
• Roof, materials and windows: a roof pitch matching the house as far as practicable, materials of similar appearance, and upstairs side windows obscure glazed and fixed shut unless they open more than 1.7 metres above the floor.

Our guide to rear extensions and side returns has the detail.

From real London projects priced in August 2026, all ex VAT and indicative rather than a quotation:

• New above ground space at a high standard, before professional fees: £2,400 to £2,800 per square metre.
• A single storey extension of around 34 m², new space only: from around £80,000, roughly £2,400 per square metre.
• Most complete extension projects, including the knock through, finishes and fittings: from around £100,000, before professional fees and planning.
• A two storey side return adding a kitchen extension with a bedroom and shower room above, around 48 m² of new floor area: around £188,000.
• Most London loft conversions: between £90,000 and £115,000, roughly £3,300 per square metre of finished space. A loft conversion of around 28 m², typically a bedroom and shower room, came to around £92,000.

These cover extensions and lofts generally, not a study alone. Within the loft band, rooflight conversions are the gentlest on budget, dormers buy real headroom for a moderate uplift, and mansards or hip to gable conversions sit at the top because they rebuild much of the roof. The house extension cost guide and loft conversion cost guide have the fuller picture, and the instant estimator prices your own house.

Five details make a room you can work in all day:

• Quiet: an upper floor or a loft sits away from kitchen and living room noise, and insulated walls and a solid door do the rest.
• Daylight without glare: a window beside the desk gives good light, while a rooflight above a screen can glare, so place the desk before fixing the windows.
• Power and data: sockets and a wired data point where the desk will go, on the first electrical drawings.
• Headroom: in a loft, put the desk where you can stand up from it.
• Storage: a built in desk and shelving, made as bespoke joinery, puts awkward space under a slope to use.

At Milford Mews in Streatham, the home office sits in an upper floor principal bedroom suite flooded with light from two sides, alongside a private sauna and a bespoke fitted wardrobe.

At Seven Oak in Chiswick, the loft conversion added an additional bedroom, a bathroom and a study area. Our guide to loft conversions with an en suite covers the rules:

• Planning: many rear dormers on houses are permitted development, up to 40 cubic metres of extra roof space on a terraced house and 50 on other houses. In conservation areas, roof extensions are not permitted development at all.
• Building regulations: always required. Where the new floor is more than 4.5 metres above the ground, as on a two storey house, the usual answer is a protected stair to a final exit, with fire doors onto it.

A garden office can be permitted development as a building incidental to the house. On a house, as of September 2026, it must be:

• Single storey, and not in front of the house.
• No more than 4 metres high with a dual pitched roof, 3 metres with any other roof, or 2.5 metres if any part is within 2 metres of a boundary.
• No more than 2.5 metres high at the eaves.
• Free of any verandah, balcony or raised platform, meaning any platform or decking over 30 centimetres high.

A detached single storey building with no sleeping accommodation is exempt from building regulations at up to 15 m², or up to 30 m² if it is at least 1 metre from every boundary or built substantially of non-combustible material. A new electrical circuit from the house is still notifiable work.

Keep it an office. The government's technical guidance on householder permitted development says an outbuilding used as primary living accommodation, such as a bedroom, bathroom or kitchen, is not an incidental use.

Five things decide the route before design starts:

• Flats and maisonettes: no householder permitted development rights, so an extension, a dormer or a garden office needs a planning application.
• Conservation areas: side extensions, rear extensions of more than one storey, single storey rear extensions beyond 3 metres, or 4 metres on a detached house, and roof extensions need permission. A garden office behind the house can still be permitted development, but not between the side wall and the boundary.
• Listed buildings: works affecting the building's character need listed building consent, and no outbuilding in its grounds is permitted development.
• The half plot limit: extensions and outbuildings together may not cover more than half the land around the original house, meaning the house as it stood on 1 July 1948, or as first built if later.
• Article 4 directions: these, and conditions on earlier permissions, can remove the rights, so check with the council.

A householder application, where needed, typically takes around eight weeks once validated.

The Planning Portal says working from home does not need planning permission unless it causes a material change of use. Permission will probably be needed if:

• The home is no longer used mainly as a private residence.
• The business brings a marked rise in traffic or people calling.
• It involves activities unusual in a residential area.
• It disturbs neighbours at unreasonable hours or causes noise or smells.

If in doubt, a certificate of lawful use can confirm the activity is not a change of use.

On business rates, GOV.UK says you do not usually pay them for using a small part of your home as an office. You may need to if customers visit, you employ people who work there, or you have made changes to your home for the business, such as converting a garage to a hairdresser's. Contact the Valuation Office, now part of HMRC, to find out whether you should be paying.

MVV designs and builds extensions and loft conversions across South West, West and South East London, and we confirm the planning route before design starts. See our house extension and loft conversion services, or talk to us about your own house.