Conservation areas cover a large share of London’s Georgian, Victorian and Edwardian housing, from the squares of Islington and Kensington and Chelsea to the villas of Blackheath and the riverside streets of Richmond. If your house is inside one, the planning route for your extension or loft changes, and so does the design brief. This guide explains what you lose, what you keep, and what a London council will want to see.
What is a conservation area?
A conservation area is an area a council has designated as having special architectural or historic interest, the character or appearance of which it is desirable to preserve or enhance. Designation is under the Planning (Listed Buildings and Conservation Areas) Act 1990. It is a control on the area, not on individual buildings; most houses in a conservation area are not listed.
London has hundreds of conservation areas across the 32 boroughs. Each usually has a published appraisal and management plan describing what matters (roofscape, brick colour, boundary treatments, window patterns) and setting out how the council will judge change. Reading that document before designing is the single best way to improve your odds.
Which permitted development rights do I lose in a conservation area?
The General Permitted Development Order treats conservation areas as “article 2(3) land” and switches off or narrows several householder classes automatically, with no need for an Article 4 direction.
| Permitted development right | Outside a conservation area | Inside a conservation area |
|---|---|---|
| Class A single-storey rear extension (3 m / 4 m) | Permitted | Still permitted unless an Article 4 direction removes it |
| Larger home extension (6 m / 8 m prior approval) | Permitted | Not available |
| Class A side extension | Permitted, single storey, half the width of the house | Not permitted |
| Exterior cladding (stone, render, timber, tiles) | Permitted | Not permitted |
| Class B roof extension or dormer (40 m³ / 50 m³) | Permitted, not on the principal elevation fronting a highway | Not permitted |
| Class C rooflights | Permitted | Permitted, within the same projection limits |
| Class E outbuilding | Permitted within height and 50% curtilage limits | Permitted, but not between a side wall and the boundary |
| Demolition of buildings and walls above the exempt size | No permission needed for most houses | Planning permission needed |
The practical effect for a typical London terrace:
- A rear dormer loft that would be a Lawful Development Certificate elsewhere becomes a householder planning application.
- A rear extension may still be permitted development, but in boroughs such as Camden, Islington, Hackney and Kensington and Chelsea many conservation areas carry Article 4 directions removing that right too. Check the council’s constraints map.
- A side infill on a semi needs planning.
Can I still build a rear extension in a conservation area?
Yes, and they are approved regularly. The questions change from “does it fit the PD limits” to “does it preserve or enhance the character of the area”. For a rear extension that usually means:
- Subordinate massing. The extension should read as an addition to the house, not a competing block: lower than the main eaves, set in from at least one boundary where the pattern of the street allows.
- Matching or complementary materials. London stock brick to match the original, or a deliberately contrasting but high-quality material such as zinc or timber where the appraisal supports contemporary additions.
- Respect for the rear elevation rhythm. Where a terrace has a consistent pattern of closet wings, an extension that fills the gap between them may be resisted; one that follows the wing may be welcomed.
- Glazing proportions. Large sliding doors are common and often acceptable on the rear, but full-width frameless glazing on a Georgian terrace will draw comment.
Where permitted development survives, we still recommend a Lawful Development Certificate (£264, 8 weeks), because the Article 4 position and the original-house measurements are exactly where assumptions go wrong.
Can I convert my loft in a conservation area?
Yes, but always through a householder planning application, because Class B does not apply. What councils look for:
- Rear dormers set well below the ridge, in from the party walls and above the eaves, clad in slate, tile or lead rather than uPVC or render. Full-width box dormers are the most common refusal in Islington and Camden conservation areas.
- Mansards where the terrace already has them or the appraisal identifies them as characteristic. Some conservation area guidance specifically supports mansards on unbroken terraces; other guidance resists any change to an intact roofline. Read the appraisal.
- Front rooflights kept small, conservation-style (flush, with a central glazing bar) and few.
- Hip-to-gable conversions on end-of-terrace and semi-detached houses are often resisted where the hipped roof is part of the street’s character.
As a ballpark, our fee for a rear-dormer loft typically falls around £2,000–£2,600 and for a mansard around £2,800–£3,400, excluding VAT and council fees; conservation-area work carries an uplift of around 15% to cover the heritage statement and the additional design work. The quote tool emails you an indicative figure for your own property.
What do London councils look for in conservation area designs?
Every borough applies the same statutory duty, but the emphasis differs:
- Kensington and Chelsea and Westminster are strict on roofscape and rear elevations visible from mews or gardens shared between terraces.
- Islington and Camden publish detailed design guidance and expect it to be followed; officers will quote paragraph numbers in refusals.
- Greenwich, Lewisham and Richmond have extensive suburban conservation areas of Victorian and Edwardian houses where the front elevation, boundary walls and front gardens carry most of the weight.
- Outer boroughs such as Bromley, Sutton and Harrow tend to have smaller, village-centre conservation areas where the setting of a church or high street dominates.
In all cases the officer will ask whether the proposal preserves or enhances. Harm is not automatically fatal, but it must be outweighed by public benefits, and a single household’s need for space rarely counts as a public benefit. Design for no harm.
How do I find out if my house is in a conservation area?
- Search the council’s online constraints or policies map by address.
- Check the property information forms from your purchase; conservation area status is a standard enquiry.
- Read the conservation area appraisal, which the council publishes with a boundary map.
- Ask us: we check designation, Article 4 coverage and planning history as the first step of every quote.
Does a conservation area change the fee or timeline?
The council fee and statutory period are the same: £528 and 8 weeks from validation for a householder application (England, from 1 April 2025, indexed each April; verify before applying). What changes is the preparation. Expect a short heritage statement, more careful elevation drawings showing materials and details, and sometimes a pre-application meeting. Our timeline holds: survey booked within 1 week, planning drawings 2–3 weeks after survey, submission within 2 working days of sign-off. If the application is refused, a householder appeal by written representations typically takes 4–6 months.
Related services
- Householder planning applications: applications and heritage statements for conservation-area homes.
- Loft conversions: dormer and mansard lofts designed for conservation-area scrutiny.
- House extensions: rear and side extensions in sensitive settings.
- Design review: an independent read of your scheme against the appraisal before you submit.
- Borough guides: Islington and Richmond upon Thames.
- Get an instant estimate for a conservation-area project.
