Premium Builders in Marylebone
High-specification refurbishment of listed townhouses, mews houses and flats in Marylebone, built to your design team's drawings under a JCT contract.
Builders in Marylebone, W1
Marylebone is Georgian terraces on Harley Street and Wimpole Street, mansion blocks around Marylebone High Street and mews houses off the squares. Westminster City Council is the planning authority, its conservation areas here include Harley Street, Portman Estate and Dorset Square, and many of the buildings are listed. Much of the work is inside flats and lateral apartments, where the landlord's licence matters as much as the council's consent.
Alstruct takes on this work as main contractor. We price from your architect's or interior designer's drawings and specification after a site visit, build under a JCT contract for a fixed, itemised sum, and start controlled work only once the consents it needs are in place. Our published case studies are elsewhere in London (Archway, Bow, Limehouse, Golders Green, Cockfosters and Stratford), not in Marylebone.
The high-specification refurbishment section below sets out the consents a Marylebone project usually needs, including the landlord's licence for alterations, and the published rates we use as a cross-check. If you already have drawings, see how pricing from your drawings works.
How we take on work in Marylebone
- Main contractor under a JCT contract, as standard
- Fixed, itemised price from your design team's drawings, after a site visit
- Written variation instructions, with any extra cost confirmed before the work is done
- A dedicated site manager coordinating the trades and Building Regulations inspections
- £10M public liability insurance
- CHAS Elite, Constructionline Gold & FMB accredited
- 10-year workmanship warranty
- Drawings and photos can be attached to the enquiry form (PDF, JPG, PNG, HEIC, DWG)
Luxury Construction Services in Marylebone
Refurbishment in Marylebone
Whole-house and apartment refurbishment in Marylebone: structural alterations, new services, joinery, stone and decoration, built to your designer's schedule under one JCT contract.
Learn more →Extensions in Marylebone
Rear and closet-wing extensions built to consented drawings, with the steelwork, glazing and finishes your architect specifies.
Learn more →Loft Conversions in Marylebone
Mansard and roof-level conversions where planning and listed building consent allow, including the structural work, stairs and fit-out.
Learn more →Basement Conversions in Marylebone
Cellar conversions and single-storey basement excavation where Westminster's basement policy and the building's listing allow, including underpinning, waterproofing and fit-out.
Learn more →Structural Works in Marylebone
Underpinning, foundations, drainage and structural alterations, designed by your engineer and inspected by building control.
Learn more →Hard Landscaping in Marylebone
Stone paving, garden walls, steps and front-area repairs, usually carried out as part of a wider refurbishment.
Learn more →House and kitchen extensions in Marylebone
Marylebone is Georgian and Victorian terraces on the Howard de Walden and Portman estates, mansion blocks around Marylebone High Street, and mews houses off the main squares. Marylebone extensions are lower-ground and basement projects, mews conversions and rear infills, needing planning permission, listed building consent where the building is listed, and often the estate's consent under the lease.
Marylebone is almost entirely conservation area with many listed buildings; Westminster City Council and the great estates control external change. As a guide, a single-storey extension costs between £2,500 and £4,000 per m², so a 25–30 m² kitchen extension is roughly £75,000–£120,000 fitted out; our house extension cost guide breaks the numbers down. We check permitted development rights at the first visit and deal with Westminster City Council in-house.
Planning a kitchen extension? See our kitchen extensions page for layouts, glazing and costs.
Loft conversions in Marylebone
Roof works in Marylebone are usually mansard roof extensions or top-floor reconfigurations agreed with Westminster's conservation officers.
Expect £45,000–£75,000 for a dormer loft with a bedroom and en-suite, £60,000–£100,000+ for a mansard and from £25,000 for a Velux conversion; the loft conversion cost guide has the breakdown. For a Marylebone loft we measure head height, roof structure and the stair landing first, and the quote includes structural calculations and Building Regulations approval.
Renovations and refurbishment in Marylebone
Marylebone projects are high-specification refurbishments of townhouses, mews houses and lateral apartments. Typical Marylebone refurbishments include structural openings with steel beams, new kitchens and bathrooms, rewiring, heating and period repairs such as sash windows, cornices and floors. See our renovation cost guide for realistic budgets. Every project is run by a single project manager under a JCT contract, with a written specification and a 10-year workmanship warranty.
High-specification refurbishment in Marylebone
Marylebone is Georgian terraces on Harley Street and Wimpole Street, mansion blocks around Marylebone High Street, and mews houses off the squares. Much of the work is inside flats and lateral apartments: layouts replanned, floors and services renewed, and kitchens, bathrooms and joinery fitted to a designer's drawings.
Westminster City Council is the planning authority, and its conservation areas here include Harley Street, Portman Estate and Dorset Square. Listed building consent covers the interior as well as the exterior; where it is unclear whether consent is needed, you can apply to Westminster for a Certificate of Lawfulness of Proposed Works.
Flats bring in a landlord. The Portman Estate's guidance says a tenant modernising a flat may need approval from both the immediate landlord and the freeholder, through a formal licence for alterations. Works that can need one include:
- structural alterations and changes to the appearance of the property
- replacing carpet with ceramic tiles or hardwood flooring, depending on the lease
- air conditioning equipment or a satellite dish on the roof
The estate may also ask for a refundable deposit. On any other estate, check the lease before design work goes far.
For houses, Westminster's City Plan supports basements of no more than one storey beneath the lowest original floor level and beneath no more than 50% of the garden land, with a margin of undeveloped garden around the boundary. Any new or extended basement needs a Construction Management Plan under the council's Code of Construction Practice, which limits audible building work to 08:00–18:00 on weekdays and 08:00–13:00 on Saturdays, with no excavation, piling or demolition on Saturdays.
We build under a JCT contract for a fixed, itemised price, working with your architect or interior designer, with £10M public liability insurance, CHAS Elite, Constructionline Gold and FMB accreditation and a 10-year workmanship warranty. Our guide rates are £1,100–£1,600/sqm for a high-specification renovation of a Victorian terrace and £4,500–£6,500 per square metre for a full basement excavation; Marylebone work is quoted by pricing from your drawings. See our high-end residential builders page. Extension figures include VAT; basement and renovation figures exclude it.
Guides for homes in Marylebone
For the period townhouses, mews and conservation areas of Marylebone, our most useful guides are mansard loft conversion costs, basement conversion costs, extending in a conservation area, leaking lead roof valleys and damp basements and tanking.
Planning approvals in Marylebone
Westminster City Council approved 83.1% of householder planning applications decided between September 2025 and August 2026, against a London average of 85.8%; a typical decision took about 11.5 weeks from validation. Extensions were approved 81.8% of the time.
See how every London borough compares, including loft and extension approval rates, in our 2026 London planning approvals study.
Alstruct projects near Marylebone
Notting Hill Villa, W11
Every lead valley renewed on a period villa roof, and the basement store waterproofed and reinstated.
View project →Archway Victorian Terrace, N19
Full Victorian terrace renovation and rear extension with triple glazing and aluminium sliding doors.
View project →Hammersmith Terrace, W6
A terraced house reworked from the lower ground floor to a new loft floor, with a new steel frame and a full refit.
View project →Beyond the projects above, we have recent and current sites in W4, W14, N6, NW8, NW6, W12 and SW6 within about five miles of Marylebone, and we work across every London borough from our office in South Woodford, E18. See all completed projects →
Common questions about building in Marylebone
Do I need planning permission for an extension in Marylebone?
A house (not a flat or maisonette) keeps national permitted development rights for a single-storey rear extension of 3m attached or 4m detached, or up to 6m or 8m through prior approval, and for most rear dormers up to 40 cubic metres on a terrace or 50 elsewhere. Most of Marylebone sits in Westminster City Council's Harley Street or Portman Estate conservation areas, with parts in Dorset Square, East Marylebone, Regent's Park and Stratford Place. Rear extension rights survive there, but side extensions, two-storey rear extensions, cladding and roof additions do not. Every basement needs planning permission under Westminster's city-wide Article 4 direction.
How does Westminster City Council treat mansard roof extensions in Marylebone?
City Plan Policy 45 supports roof extensions in principle where they do not harm heritage assets and follow a roof form already established in the terrace. On Georgian and Victorian terraces a mansard is often the most appropriate form, but further storeys on an unaltered group are usually unacceptable, and on a uniform terrace the council looks for a coordinated approach across the whole row. The Harley Street conservation area audit (2008) also maps roofs where extensions are unlikely to be accepted. Each scheme is decided through a planning application.
What does a mansard loft conversion cost in Marylebone?
Our London figures for a mansard loft conversion are £60,000–£100,000+ including VAT, with prime central schemes at £120,000–£150,000. On Marylebone's Georgian terraces the cost depends on the party walls, the existing roof structure and whether the house is listed, and we price from your architect's drawings after a site visit. The mansard loft conversion cost guide sets out what each figure covers.
Which Alstruct projects are nearest to Marylebone?
Notting Hill Villa, W11, about 2.3 miles away, is the closest: every lead valley on a period villa roof was renewed and the basement store waterproofed and reinstated. Archway Victorian Terrace, N19, about 3.2 miles away, was a full Victorian terrace renovation and rear extension with triple glazing and aluminium sliding doors. Hammersmith Terrace, W6, about 3.8 miles away, was a terraced house reworked from the lower ground floor to a new loft floor, with a new steel frame and a full refit.
Which parts of Marylebone do you cover?
We cover Marylebone across W1, including the Harley Street and Wimpole Street terraces, the mansion blocks around Marylebone High Street and the mews houses off the squares. Westminster City Council is the planning authority. Our office is in South Woodford, E18, about 9 miles away, and nearby we also cover St John's Wood, Mayfair and Camden.
Nearby areas we cover
Alstruct works across every London borough. Here are areas close to Marylebone with dedicated local pages: