House Extensions Marylebone
Single storey rear and double storey extensions in Marylebone, planning, structure and build under one contract.
- Rated 4.9 from 31 reviews on MyBuilder
- Single-storey rear extension from £40,000
- Free site survey, itemised quote
Extending in Marylebone is different from extending a suburban house, and GS Renovation draws on our founder's 30+ years on the tools to work within those limits. The area's red-brick mansion blocks and purpose-built period flats in W1 offer little room to build outward, so most projects reconfigure and enhance the existing footprint rather than add to it.
In Marylebone, a single-storey rear extension typically starts from £40,000, or £2,000 to £2,800 per m² (indicative London ranges, Architecture for London, Resi, MyBuilder and Checkatrade, 2026). GS Renovation Ltd, a building contractor based in Potters Bar, does the work in Marylebone: the structural engineer we appoint designs the structure, we build it, and building control signs it off.
Price guide
| Work | Indicative London range |
|---|---|
| Single-storey rear extension | from £40,000 |
| Rear extension, per m² | £2,000 to £2,800 |
| Side return, per m² | £2,400 to £3,200 |
| Wraparound, per m² | £2,400 to £3,200 |
| Double storey, per m² | £1,800 to £2,600 |
| Basement extension | see the basement page |
Indicative London ranges (Architecture for London, Resi, MyBuilder and Checkatrade, 2026), not a quotation. Prices checked September 2026. Full breakdown: Extension Costs & Planning.
Quick estimate for Marylebone
Marylebone range: choose above
What extending means in Marylebone W1
Permitted development rights that let owners of houses add rear or side-return extensions do not apply to a Marylebone flat, and much of the area sits within conservation controls under Westminster City Council. That means external alterations, roof changes or anything affecting the appearance of a period block will almost always need planning permission, and listed buildings need listed building consent on top of it.
For most leaseholders the realistic gain is internal. We create the sense of an extension by opening up dividing walls, absorbing under-used space and reworking tired layouts, all sized by an engineer and signed off under building regulations. Where a genuine addition is possible, such as a mansard or a rear infill on a house, we work with your architect on the planning application to the council from the start.
Housing in Marylebone
Of the 12,620 homes the valuation list records in Marylebone, 54% were built before 1919, 16% between the wars and 29% since 1945; 92% are flats and 8% are houses. A flat in Marylebone has no householder permitted development rights, so extending one needs planning permission and the freeholder's consent, which matters here because most homes are flats.
Extending one of the few Marylebone houses
8% of Marylebone homes are terraced houses and 92% are flats, so an extension here is a question for a small number of owners on tight plots. Westminster's guidance on development in conservation areas says extensions should respect the scale and proportions of the existing building and must be architecturally subordinate to the main building. On a Georgian terrace that points to an addition that stays visibly lower and narrower than the house, with the structural engineer we appoint designing the openings into the original rear wall around the brickwork that stays.
The same guidance says full width rear extensions are generally not acceptable, except in certain circumstances at basement level. Before paying for a full set of drawings, use Westminster's householder pre-application service for an unlisted house, which gives written advice only on a 28 day timescale. The advice fixes the footprint, and the footprint fixes the steel, the drainage run and the party wall notices the building owner will serve. Programming the Marylebone build from an agreed footprint avoids the redesign that follows a refusal.
Foundations, steel and fit-out near Hyde Park
When a scheme does involve building work, whether a lower-ground rear infill on a townhouse near Hyde Park or a roof addition, we cover the whole sequence. That means groundworks and foundations designed for the tight, built-up plots typical of central London, steel beams to carry new openings, roof and weathering works, and a full fit-out with plastering, electrics, plumbing and decoration.
Access and logistics shape every W1 job. There is no wide driveway to store materials, deliveries have to thread through busy streets near Oxford Street and the West End, and party structures are shared with neighbours. We plan skips, scaffolding and deliveries around those constraints, give you the drawings for any party wall notices you serve, and keep the freeholder and managing agent updated throughout the build.
Kitchen extensions in Marylebone
92% of homes in Marylebone are flats, and a flat has no householder permitted development, so a ground-floor flat's kitchen extension needs planning permission from Westminster City Council and the freeholder's consent. With so few houses here, the realistic kitchen gain in most Marylebone homes is a better layout inside the flat rather than an extension. The fit-out is priced on its own page, kitchen renovation in Marylebone; the build figures are in the table above. Double storey extensions belong to the few houses here.
- Single and double storey extensions
- Party wall process explained, and the extension built to the award
- First fix and second fix plumbing and electrics throughout
VOA Council Tax stock of properties, March 2025, for Marylebone & Park Lane and Bryanston & Dorset Square. Counts rounded by the VOA.
Why Choose GS Renovation in Marylebone
GS Renovation is honest from day one about what a Marylebone property can and cannot support, which saves owners wasted time and fees. We know when a scheme needs planning permission from Westminster versus building regulations alone, we coordinate the freeholder's consent and the party wall side, with the notices served by you as building owner, and our founder's 30+ years on the tools mean we build cleanly on constrained W1 plots.
- Building control inspected at foundation, damp course and steel stages
- Permitted development checked before you pay for a planning application
- Aftercare and snagging support once the job is finished
Built a new extension at rear of property. Laid foundations, drainage, raised floor, new roof and completed all fixtures and interior decoration…
George always kept to commitments and arrived on time. He offered helpful suggestions during his initial visit and promptly provided a reasonably…
Saaid is the best craftsman I have worked with. He knows what he is doing from the very beginning. He has a great knowledge of construction…
FAQ
Frequently Asked Questions about House Extensions Marylebone
What is the going rate for house extensions around Marylebone?
Three Westminster builders will give three different numbers for house extensions in Marylebone, usually because they have scoped three different jobs within £2,000 to £2,800 per m² for a rear extension (indicative). GS Renovation prices the W1 property after a survey and sets out labour, materials, approvals and making good in the order they happen: the planning route is confirmed before drawings, and footings inspected before concrete.
Do I need planning permission to extend my Marylebone property?
Usually yes for anything external. Flats have no householder permitted development rights, and much of W1 falls under conservation and listed controls, so alterations to a period block typically need planning permission from Westminster City Council. Internal reconfiguration is different and is governed by building regulations. We assess your specific building before you commit to any design.
Can a Marylebone flat be extended at all?
Occasionally. Flats carry none of the automatic extension rights that houses enjoy, so every Marylebone flat extension is a full application to Westminster City Council, and with conservation areas across much of the district the design is judged closely. The freeholder must sign off under the lease, and building control inspects whatever is eventually approved.
Does a lower-ground infill on a Marylebone townhouse need party wall notice?
Usually. Marylebone townhouse plots are tight, so trenches for a rear infill almost always fall inside the 3 metre zone next to the adjoining houses, and if they go deeper than those houses' footings you serve the owners one month's notice. Where a lower-ground floor already sits below the neighbour's level, the depth comparison needs care, so we check their foundation depth before the notice is served.
Does a roof addition on a Marylebone building need structural checks first?
Yes. An extra storey adds weight to walls and footings that were designed for the original height, so an engineer tests their capacity before anything is drawn. Planning permission from Westminster City Council is required, the new walls and roof must reach current Part L insulation levels, and building control inspects the steel, timbers and insulation before they are hidden.
What happens to the drains under a Marylebone townhouse extension?
They are traced with a camera before the design is fixed. Under Part H, putting new building over or close to a public sewer requires the water company to agree, which can move the foundations or the footprint of a Marylebone infill. Private drains running under the new floor may be rerouted into a fresh manhole, and the inspector sees the new runs and gradients before backfilling.
Does a Marylebone house extension pay the Community Infrastructure Levy?
Only above a size threshold, unless it creates a new dwelling. Westminster charges CIL per square metre on new dwellings of any size and on any development where the internal area of a new building, extension or change of use exceeds 100 square metres. Relief exists for some householder extensions, but it has to be claimed before work starts. Check the total new internal area at sketch stage, including any space added below ground.
Can a Marylebone terrace be extended across the full width of the garden?
Rarely at ground level. Westminster's conservation area guidance says full width rear extensions are generally not acceptable, except in certain circumstances at basement level. East Marylebone, designated a conservation area in 1982 and extended in 1990, is one of the areas it covers, so check which boundary the house sits inside first. Where the guidance applies, plan a part width addition and keep the rest of the original rear wall visible.
What makes a Marylebone extension design subordinate in Westminster's terms?
Westminster's guidance says extensions should respect the scale and proportions of the existing building and must be architecturally subordinate to it. In practice that means lower, narrower and simpler than the house it serves. On a Marylebone terrace the original rear elevation and its windows should still read clearly once the addition is built. A pre-application enquiry tests the design against that before it is fixed.
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