Westminster's most space-efficient loft solution when PD-route dormers are blocked. Our chartered team designs mansards that get approved in Westminster conservation areas — with heritage statements and planning officer negotiation built in.
For Westminster homeowners in Grand Georgian and Regency terraces in Belgravia and Pimlico; Victorian and Edwardian mansion blocks; heritage-rich townhouses throughout; very high listed building density, a mansard roof extensions package is the full measured-survey-to-submission drawing set City of Westminster needs in order to determine an application: existing and proposed plans, elevations and sections at 1:100 and 1:50, a location and site plan, and the supporting statements the case officer asks for.
Prepared and reviewed by the chartered technologist team at Architectural Drawings London — MCIAT chartered, £2m PI insured.Last reviewed 2026-08-03.
Westminster's most space-efficient loft solution when PD-route dormers are blocked. Our chartered team designs mansards that get approved in Westminster conservation areas — with heritage statements and planning officer negotiation built in.
Housing stock in Westminster: Grand Georgian and Regency terraces in Belgravia and Pimlico; Victorian and Edwardian mansion blocks; heritage-rich townhouses throughout; very high listed building density.
Character: Heritage-first planning approach; listed buildings on almost every street; basement and rear extension policies particularly strict.
Article 4: Multiple Article 4 Directions — office-to-residential restrictions, HMO conversions, retail to residential in shopping zones.
Basement policy: Westminster basement policy restricts to single-storey, typically under 50% of rear garden footprint; lightwells and rooflights strictly controlled in conservation areas.
We check against Westminster City Council's mansard design guide and design to match the terrace.
Required for Westminster's conservation areas — demonstrates the mansard respects character and townscape.
Accurate photomontage showing how the mansard sits alongside neighbours — often decisive at Westminster City Council committee.
Mansards invariably trigger Party Wall notices in Westminster's dense terraced streets. Structural package includes new ridge, tie beams, floor joists.
Full liaison with Westminster City Council planning officer, committee representation if called in.
Part L thermal, Part B fire (critical on mansards), Part E acoustic separation.
Single planning or regs submission.
Planning + building regs + structural.
Listed, conservation, complex sites.
Move the controls for an indicative figure. It anchors your budget — it is not a quote. Every project is priced after a free survey.
Build costs are separate and quoted by your contractor. See our published fees.
Every Westminster postcode district we draw in, the stock that dominates it and the authority that validates a mansard roof extension there. Westminster fees below are the statutory England rates for 2026, not mansard roof extension estimates.
| Postcode | Area | Dominant stock | What it means for a mansard roof extension |
|---|---|---|---|
| W1H | Marylebone | Georgian terraces, Edwardian mansion blocks | Marylebone sits wholly inside W1H, so Westminster City Council validates every mansard roof extension submitted from an W1H address. |
| W1J | Mayfair | Georgian townhouses, listed buildings | A mansard roof extension at an W1J address in Mayfair is determined by Westminster City Council under its own Local Plan policies for Mayfair. |
| W1S | Mayfair / Hanover Square | Grand Georgian and Regency terraces in Belgravia and Pimlico; Victorian and Edwardian mansion blocks; heritage-rich townhouses throughout; very high listed building density | Mayfair / Hanover Square sits wholly inside W1S, so Westminster City Council validates every mansard roof extension submitted from an W1S address. |
| W1W | Fitzrovia / Great Portland Street | Grand Georgian and Regency terraces in Belgravia and Pimlico; Victorian and Edwardian mansion blocks; heritage-rich townhouses throughout; very high listed building density | W1W covers Fitzrovia / Great Portland Street only; Westminster City Council handles the mansard roof extension, and Fitzrovia / Great Portland Street case officers apply the W1W conservation-area map. |
| W2 | Bayswater / Paddington | Victorian stucco terraces | W2 covers Bayswater / Paddington only; Westminster City Council handles the mansard roof extension, and Bayswater / Paddington case officers apply the W2 conservation-area map. |
| W9 | Maida Vale | Victorian terraces, mansion blocks | W9 covers Maida Vale only; Westminster City Council handles the mansard roof extension, and Maida Vale case officers apply the W9 conservation-area map. |
Roof pitch, wall build-up and plot depth change every few Westminster streets, and each one changes what a mansard roof extension can achieve at that address.
Westminster conservation designations: there are 56 across Westminster City Council, St John's Wood, Mayfair, Belgravia among them. Designation costs a Westminster owner the permitted-development route: a mansard roof extension then needs a £548 householder application over 8 weeks, in place of the £249 prior approval route that takes 6 weeks. Covent Garden is the Westminster designation that most often changes a mansard roof extension design.
What Article 4 removes near Westminster: Multiple Article 4 Directions — office-to-residential restrictions, HMO conversions, retail to residential in shopping zones. Before pricing a mansard roof extension we check whether the NW8 address is inside the mapped area, because Westminster City Council draws the Westminster boundary street by street rather than across the whole of Westminster.
Digging below a Westminster property: Westminster basement policy restricts to single-storey, typically under 50% of rear garden footprint; lightwells and rooflights strictly controlled in conservation areas. Where a mansard roof extension in Westminster involves excavation that is read beside the Party Wall etc. Act 1996, which needs two months notice for a Westminster dig within 3 m of a neighbour, and Westminster City Council expects the NW8 ground conditions addressed in the application.
The building fabric around Westminster: Grand Georgian and Regency terraces in Belgravia and Pimlico; Victorian and Edwardian mansion blocks; heritage-rich townhouses throughout; very high listed building density. Heritage-first planning approach; listed buildings on almost every street; basement and rear extension policies particularly strict. A mansard roof extension in Westminster is scoped against that stock first, because it decides whether the scheme runs as permitted development, a £274 Lawful Development Certificate, or a full £548 application to Westminster City Council.
Sources for this Westminster mansard roof extension page: borough policies maps and conservation-area registers (2025–26), Royal Mail postcode district boundaries, the Town and Country Planning (Fees for Applications) (England) Regulations, the Town and Country Planning (General Permitted Development) (England) Order 2015 as amended, and the Party Wall etc. Act 1996.
Of 217 listed building and conservation area consent appeals decided in Westminster over the window covering appeals decided 2016-2026, Westminster sat close to the London norm, with 28.1% of appeals succeeding against 28.5% city-wide. 61 were allowed and 147 dismissed, with 9 split. Mansards concentrate on terraces in conservation areas and on listed buildings, where consent runs separately from planning permission. These 217 Westminster consent appeals are the contested minority.
Half of those Westminster appeals took more than 105 days to decide from the day the appeal started — time added on top of the council's own determination period, which is the argument for getting the application right first. 18.9% of them (41 cases) involved a conservation area, so heritage argument carries real weight in Westminster. 13.4% affected the setting of a listed building. 94.5% were decided by written representations rather than a hearing or inquiry, meaning the written case and the drawings were the whole of the evidence.
217 listed building and conservation area consent appeals decided in Westminster. Source: Planning Inspectorate casework, OGL v3.0.
Direct answers to the questions Westminster homeowners ask every week about mansard roof extensions.
Start a free quote →Mansards in Westminster are more heavily scrutinised than in outer boroughs. Westminster City Council prioritises heritage and townscape — approvals require exceptional design quality, clear precedents on the street, and a full Heritage Statement. We've delivered mansard approvals in the borough; each application is bespoke.
A 70° front slope is typical for Westminster mansards — steep enough to maximise floor area while reading as a roof rather than a full additional storey. Front dormers should be small and symmetrical. Westminster City Council's design guide (where published) takes precedence on detail.
Often yes, but Westminster City Council favours applications supported by wider street precedents. Where mansards already exist nearby in Westminster, approval is far more likely. We review street precedents at the feasibility stage.
A Westminster mansard carries more design work than a dormer — heritage statement, street-elevation massing and conservation-led detailing on top of planning, building regulations and structural calculations. Build cost then varies with size, roof geometry and site access. Our design fee is fixed before we start; see our fees.
Full-height — typically 2.3–2.5m ceiling from the new floor. Unlike a dormer, which gives partial head height, a mansard provides a complete additional storey within Westminster's grand Georgian and Regency terraces in Belgravia and Pimlico terraced context.
We cover all Westminster postcodes — SW1, W1, W2, W9, NW1, NW8, WC2 — and have submitted mansard applications across the borough. Our heritage statement and design-and-access statement are included in every mansard package.
Westminster's grand Georgian and Regency terraces in Belgravia and Pimlico terraced stock is the natural context for mansard extensions — they were originally designed for Victorian and Edwardian rows. Feasibility depends on street precedent, conservation area status and party wall implications. We assess all three at the free site visit.
A mansard adds a full upper storey — typically 35–45m² of usable floor space. In Westminster this often converts a 3-bed house to 4 or 5 beds. The steep front slope (70°) and flat top read as a roof, not a full floor, which is why Westminster City Council accepts them more readily than a simple box extension.
If your property sits on a boundary, here are the neighbouring options.
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