Loft conversion in London
A loft conversion turns unused roof space into habitable rooms — typically a main bedroom with en-suite. The common London forms: rooflight conversions (no volume change), rear dormers (the volume workhorse), hip-to-gable on semis, and full mansards on Victorian terraces where the streetscape supports them.
It is usually the most cost-effective space a London house can add: no foundations, no garden lost, and the new floor area lands in the highest-value use — bedrooms. The constraints are headroom (2.2m+ at the ridge to be viable), stair position, and — in conservation areas — the roofline itself.
The planning route — PD or permission?
Permitted development (GPDO Class B) allows roof enlargements up to 40m³ on terraced houses and 50m³ on semis and detached — enough for a substantial rear dormer — provided nothing projects beyond the roof plane of the principal elevation, materials are similar, and dormers sit back from the eaves. Class B is excluded in conservation areas.
In conservation areas the route is a full application, and roof form decides it: rear mansards with traditional slate and proportioned dormers have a strong record on Victorian terraces; box dormers and front-facing alterations are the classic refusals. Article 4 directions (Muswell Hill is the local example) pull roof works into planning control even where conservation policy alone might not.
Whatever the route, building regulations approval is always required — fire escape, stair geometry and floor structure — and a Lawful Development Certificate is cheap insurance on PD schemes.
Do you need planning permission for a loft conversion?
| Roof volume added — terraced house | Up to 40m³ |
| Roof volume added — semi-detached or detached | Up to 50m³ |
| Principal (street-facing) roof plane | No extension beyond it |
| Dormers | Set back from the eaves; materials similar |
| Conservation areas | Class B excluded — full permission |
| Flats | Always need permission |
| Building regulations | Always required, whatever the planning route |
Limits summarise the General Permitted Development Order (Schedule 2, Part 1) as it applies in London. Conservation areas, Article 4 directions and listed status change the route — check your own address before relying on them.
What it really costs
| Cost per m² (low — rooflight conversion) | £3,000 |
| Cost per m² (expected — rear dormer) | £3,700 |
| Cost per m² (high — mansard, conservation spec) | £4,500+ |
| Typical project (20–28m² with bathroom) | £86,000 – £180,000 |
| Professional fees, surveys, party wall (add) | 8–15% of build |
Mansards in conservation areas sit at the top of the range — natural slate, lead detailing and officer negotiation all cost. Ranges calibrated from real project data; VAT excluded.
Realistic timeline
| Design and drawings | 4–6 weeks |
| PD route (Lawful Development Certificate) | 4–8 weeks |
| Full application (conservation areas) | 8–12 weeks (8-week statutory target) |
| Party wall award | 4–8 weeks (parallel) |
| Build | 10–14 weeks |
What catches people out
- Conservation areas removing the PD route — the difference between a certificate and a contested application.
- Headroom under 2.2m at the ridge making the scheme marginal before it starts.
- Stair position consuming a first-floor room and souring the floor plan.
- Party wall: steels bear on shared walls on every terrace conversion.
- Fire regulations on three-storey houses — protected stair enclosure and escape windows priced in late.
Loft conversions, borough by borough
Mansards with natural slate have strong precedent on conservation-area terraces.
Loft conversion in Camden →Roof-level changes face the strictest control in London — precedent and heritage statements essential.
Loft conversion in Westminster →Follow the street's established roof pattern and rear dormers approve routinely.
Loft conversion in Islington →Deep PD precedent outside the conservation cores; protected rooflines are the refusal zone.
Loft conversion in Hackney →The borough's signature project — Edwardian N8/N10 stock converts beautifully, with dormer design decisive.
Loft conversion in Haringey →Roof-level change in the conservation areas faces intense control; mansard form and natural slate decide outcomes.
Loft conversion in Kensington and Chelsea →Rear dormers approve on many terraces under PD; conservation-area rooflines need a full application.
Loft conversion in Hammersmith and Fulham →Rear-dormer lofts are common on the Camberwell and Dulwich terraces; protected rooflines are the refusal zone.
Loft conversion in Southwark →Follow the street's roof pattern and rear dormers approve well; conservation and Article 4 areas need an application.
Loft conversion in Lambeth →Workable outside the conservation areas; the listed Georgian roofs of Spitalfields are off-limits without consent.
Loft conversion in Tower Hamlets →Strong loft stock; conservation-area dormers and rooflines get the closest scrutiny.
Loft conversion in Wandsworth →Feasible on much of the suburban stock under PD; in the borough's many conservation areas, dormer form and a full application are the rule.
Loft conversion in Richmond upon Thames →The interwar semis convert readily under PD; in HGS, Mill Hill, Totteridge and the other Article 4 areas a full application is needed.
Loft conversion in Barnet →Strong on the Victorian and Edwardian stock of Hanwell, Acton and West Ealing; conservation areas scrutinise dormer design.
Loft conversion in Ealing →Common across Wimbledon, Colliers Wood and Morden; the John Innes and Wimbledon conservation areas decide dormer form via a full application.
Loft conversion in Merton →Routine on the Surbiton, New Malden and Worcester Park stock under PD; conservation areas require a full application and careful dormers.
Loft conversion in Kingston upon Thames →A staple on the interwar suburban stock; the borough's roof-alteration Article 4 and conservation areas can require permission for some dormers — check first.
Loft conversion in Bromley →Strong on the interwar semis of Pinner, Stanmore and Kenton under PD; the Harrow on the Hill and Pinner conservation areas scrutinise dormer design.
Loft conversion in Harrow →Common across Willesden, Kingsbury and Wembley under PD; Brent's conservation areas (all Article 4) decide dormer form via a full application.
Loft conversion in Brent →Routine on the terraces and semis of Charlton, Eltham and Plumstead under PD; the conservation areas scrutinise dormers.
Loft conversion in Greenwich →A staple on the Victorian stock of Brockley, Forest Hill and Sydenham; the Article 4 conservation areas decide dormer form via a full application.
Loft conversion in Lewisham →Common on the interwar stock of Southgate, Palmers Green and Winchmore Hill under PD; the conservation-area Article 4 directions scrutinise dormers.
Loft conversion in Enfield →Routine on the Walthamstow, Leyton and Chingford stock under PD; Walthamstow Village and the other conservation areas decide dormer form.
Loft conversion in Waltham Forest →Strong on the interwar semis of Sutton, Cheam and Worcester Park under PD; the conservation areas scrutinise dormer design.
Loft conversion in Sutton →Common across suburban Croydon under PD; the Article 4 conservation areas (the Waldrons, the Webb Estate) decide dormer form via a full application.
Loft conversion in Croydon →Routine on the Bexleyheath and Sidcup semis under PD; the conservation areas scrutinise dormers.
Loft conversion in Bexley →Common on the Chiswick and Isleworth stock; Bedford Park and the heritage areas decide dormer form via a full application.
Loft conversion in Hounslow →Strong on the Ruislip and Eastcote semis under PD; the village conservation areas scrutinise dormer design.
Loft conversion in Hillingdon →Common on the Ilford and Woodford semis under PD; the Wanstead and Snaresbrook conservation areas decide dormer form.
Loft conversion in Redbridge →Routine on the Hornchurch and Upminster semis under PD; Gidea Park and the conservation areas scrutinise dormers.
Loft conversion in Havering →Common on the Forest Gate and East Ham terraces; the Woodgrange Estate Article 4 area decides dormer form via a full application.
Loft conversion in Newham →A staple on the Becontree and Dagenham stock under PD; the conservation areas scrutinise dormers, and an upward-extension Article 4 can apply.
Loft conversion in Barking and Dagenham →Barely relevant — the City's listed flats can't be loft-converted by a household; alterations need listed building consent.
Loft conversion in City of London →Loft conversion planning, area by area
Usually a full application — and the roof form decides it.
Do I need permission? →Usually a full application — and often not available at all if you're in a converted flat.
Do I need permission? →Usually a full application — permitted-development loft rights are removed in the conservation area and the Article 4 directions reinforce it.
Do I need permission? →Usually a full application on a house, and typically not possible on a mansion-block flat.
Do I need permission? →In most of Maida Vale, a loft conversion isn't available to you — the mansion blocks are flats whose roofs are common parts owned by the freeholder.
Do I need permission? →On the Nash terraces, effectively no — roof alterations to a Grade I-listed composition are not the kind of change that gets consent.
Do I need permission? →Loft conversions, asked straight
How much does a loft conversion cost in London?
Do I need planning permission for a loft conversion?
Dormer or mansard — what's the difference?
How much value does a loft add?
Can every house take a loft conversion?
Related reading
Almost every London extension, loft and basement engages this Act. Here's how it actually works.
Read the guide →40 cubic metres of opportunity — unless your street says otherwise.
Read the guide →Your lease is a contract — and the council was never the only gatekeeper.
Read the guide →Could you build one at your address?
The rules above bend at address level — conservation areas and Article 4 directions change the route entirely. Run the live constraint check before you spend on drawings.
Planning Permission Checker provides planning and cost intelligence for early feasibility only. It is not legal, planning, valuation, architectural, structural, or surveying advice. All estimates are indicative and must be verified by qualified professionals before purchase, design, planning submission, or construction.
Cost estimates are indicative only — not a quotation. Final price depends on survey, specification, structure, access, party wall matters, VAT, professional fees, and contractor availability.
Planning outcomes are not guaranteed. Local planning authorities make final decisions.