High-End Residential Builders in London
High-specification refurbishments, extensions and basements for period and listed London homes, built to your architect's drawings under a JCT contract.
A main contractor for high-specification London homes
Alstruct builds high-specification refurbishments, extensions and basements for owners of period and high-value homes in London, and for the architects and interior designers acting for them. We price from your design team's drawings, sign a JCT contract at a fixed, itemised price, and run the site under one site manager through to handover.
This page is for anyone comparing contractors for a listed townhouse, a lateral flat or a house on one of the central London estates. It covers how we take the work on, the consents that govern it and what it costs.
How Alstruct takes on high-end residential work: a JCT contract as standard; a fixed-price, itemised quote built from your architect's or designer's drawings and a site visit; £10M public liability insurance; CHAS Elite and Constructionline Gold accreditation and Federation of Master Builders membership; and a 10-year workmanship warranty that runs from practical completion and passes to the next owner if you sell.
What high-specification work involves
High specification is less about expensive finishes than about tolerance, sequence and paperwork. The drawings are more detailed, more of the building is protected, more consultants have a say, and mistakes are harder to hide.
Five kinds of work and what each demands
Whole-house refurbishment
Strip-out, structural alterations and steelwork, full rewiring and plumbing, plastering, joinery, kitchens, bathrooms and decoration under one contract. In a period house the order matters: structure first, then first-fix services, then plaster, so that finished work is never opened up again. See home renovations.
Listed building and conservation-area work
The consented drawings define what may be touched. Listing protects the interior as well as the exterior, so cornices, fireplaces, floorboards and even plaster can be controlled. We build what the consent allows, and any change is agreed and instructed in writing before the work is done. Our conservation area guide covers materials.
Basements and structural alterations
Underpinning in sequence, a reinforced concrete structure, waterproofing and pumped drainage. We investigate the site with trial pits before recommending an approach, specify a combined structural and cavity-drain waterproofing system, and fit dual pumps with battery backup and high-level alarms. See basement conversions.
Extensions with structural glazing
Steel frames, wide openings into the existing house and large-format glass, where steel, roof and glazing must be set out to the same tolerances. At our published Lyal Road project in Bow, the structural roof glazing followed the steel frame and flat roof, with leadwork and box gutters detailed around it. See house extensions.
Interior fit-out to a designer's specification
Joinery, stone, sanitaryware, ironmongery and lighting priced and installed against the interior designer's schedules. Items supplied or specified by you or your designer are covered by their own manufacturer warranties where available; our 10-year warranty covers our workmanship.
Consents in prime central London
Belgravia, Mayfair and Marylebone come under Westminster City Council; Kensington and Chelsea under the Royal Borough of Kensington and Chelsea. Boundaries do not follow neighbourhood names exactly, so confirm the authority for your address. Your architect or planning consultant secures the consents; the builder's job is to know what they allow, and to build nothing that needs a consent until it exists.
Listed building consent
Government guidance says any works to alter or extend a listed building in a way that affects its character require listed building consent, and that listing covers the entire building, internal and external. Carrying out such works without consent is a criminal offence under the Planning (Listed Buildings and Conservation Areas) Act 1990, and Historic England notes that the planning authority can insist the work is reversed.
Basements
Both councils limit basements in their local plans. Kensington and Chelsea requires basement development to comprise no more than one storey, to cover no more than 50 per cent of each garden, and not to involve excavation underneath a listed building, including vaults. Westminster supports basements that extend beneath no more than 50% of the garden land and comprise no more than one storey beneath the lowest original floor level; in a listed building they must not unbalance the original hierarchy of spaces.
Codes of construction practice and working hours
Each council has a Code of Construction Practice, and basement schemes must submit a construction management plan under it. In Kensington and Chelsea, work audible at the site boundary is permitted from 8am to 6pm, Monday to Friday, and at no time on Saturdays, Sundays or public holidays. In Westminster it is permitted 08:00–18:00 Monday to Friday and 08:00–13:00 on Saturdays, but piling, excavation and demolition are not permitted on Saturdays.
Estate consent
The landed estates add a private layer. Grosvenor says freehold owners in Belgravia and Mayfair need its consent alongside statutory permissions and cannot proceed without both. Cadogan tells its Chelsea leaseholders that alteration is generally prohibited without the landlord's consent, which is given through a Licence to Alter. The Portman Estate in Marylebone requires a formal licence for alterations. Read the alterations clause in your lease before the design is fixed.
What it costs
Prime central London projects are priced from the design team's drawings, not from a rate card. The figures below are the upper tiers of the cost guides on this site: London-wide rates to sense-check a budget, not to set one.
| Work | Published guide rate | Source |
|---|---|---|
| Extension, high-spec | £3,200–£4,500/m² | House extension cost guide |
| Extension, ultra-premium | £4,500–£6,000+/m² | Same guide |
| Basement, full excavation (dig-down) | £4,500–£6,500 per m² | Basement conversion guide |
| Basement, cellar conversion | £2,500–£4,000 per m² | Same guide |
| Renovation, high-specification | £1,100–£1,600/sqm | Victorian terrace renovation cost guide |
| Renovation, full structural | £1,200–£2,000/sqm | Same guide |
Extension figures include VAT at 20%. Renovation figures are for a Victorian terrace, for construction works only, before VAT and professional fees. Basement figures include structural works, waterproofing, mechanical and electrical installation and a standard fit-out, and exclude VAT. Listed fabric, conservation-grade materials and restricted access add to all of them.
Working with your architect and designer
Most projects at this level are designed before a builder is chosen, then put out to tender. Our published Hawthorn Cottage project in Limehouse was won that way, with the client acting as project architect. Send us the drawings, specification and schedules: we take off quantities, prepare a bill of quantities and build the costs up from first principles, then return a price itemised by trade.
On site we work to your architect's or interior designer's drawings, with a dedicated site manager coordinating the trades and Building Regulations inspections. Any change to the scope is priced and confirmed in writing before the extra work is done, and at handover you receive a pack with all certificates and warranties. More on pricing from your drawings.
Areas
We work across London. These five area pages set out the council, estate and conservation position for each neighbourhood:
- High-end builders in Belgravia, SW1
- High-end builders in Mayfair, W1
- High-end builders in Kensington, W8
- High-end builders in Chelsea, SW3
- High-end builders in Marylebone, W1
We also have pages for Hampstead, St John's Wood, Notting Hill, Highgate, Richmond and Wimbledon.
Published projects
The case studies published on this site are in north and east London, not in the postcodes above. We list them here because they show the disciplines this work depends on: underpinning, structural steel, large-format glazing, period repairs and full services replacement under one contract.
For owners, architects and interior designers
Send your drawings for a fixed, itemised price
Attach plans, specifications and photos to your enquiry (PDF, JPG, PNG, HEIC or DWG; up to 10 files, 25 MB each), or book a site visit first. We contract on a JCT form, and every job carries our 10-year workmanship warranty.
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Frequently Asked Questions
Do you work under an architect or interior designer?
Yes. We work with your architect or interior designer from tender to handover: pricing from their drawings and specification, building to their information on site, and confirming any change to the scope in writing, with its cost, before the extra work is done. The contract is a JCT form at a fixed, itemised price. If you have no design team yet, our in-house architectural support can develop the scheme with you.
How do you price a high-specification refurbishment?
From the drawings, not from a rate per square metre. We take quantities off your design team's drawings, prepare a bill of quantities and build the costs up from first principles, and you receive a fixed-price quote itemised by trade. As a sense-check, our published guide gives £1,100–£1,600/sqm for a high-specification renovation of a Victorian terrace and £1,200–£2,000/sqm for a full structural renovation, before VAT and professional fees. Listed fabric and conservation-grade materials add to those rates.
Do you take on listed buildings and conservation-area work?
Yes, as the contractor building a consented scheme. Government guidance says works that alter or extend a listed building in a way that affects its character need listed building consent, that listing covers the entire building, internal and external, and that carrying out such works without consent is a criminal offence. So the consent and approved drawings must be in place before we start, and any change is agreed in writing first. Our published projects include period repairs such as reinstated cornices and picture rails.
Can you build a basement in Westminster or Kensington and Chelsea?
Yes, within each council's policy. Kensington and Chelsea requires basements to comprise no more than one storey, cover no more than 50 per cent of each garden, and involve no excavation underneath a listed building. Westminster supports basements beneath no more than 50% of the garden land and no more than one storey below the lowest original floor level. Our basement guide puts full excavation at £4,500–£6,500 per square metre; we quote a fixed price from your architect's and engineer's drawings.
What working hours do Westminster and Kensington and Chelsea allow for building work?
It depends on the borough. Kensington and Chelsea permits work audible at the site boundary from 8am to 6pm, Monday to Friday, and at no time on Saturdays, Sundays or public holidays, with demolition and concrete-breaking held to 9am to noon and 2pm to 5.30pm. Westminster permits audible building work 08:00–18:00 Monday to Friday and 08:00–13:00 on Saturdays, but not piling, excavation or demolition on Saturdays. Noisy work is programmed around those hours.
Where are your published projects?
The case studies on this site are in Archway N19, Limehouse E14, Bow E3, Cockfosters EN4, Golders Green NW11 and Stratford. None is in Belgravia, Mayfair, Chelsea, Kensington or Marylebone, and we do not claim otherwise. They show the work this kind of project depends on: underpinning, structural steel, structural glazing, period repairs and complete services replacement, built under a JCT contract with a 10-year workmanship warranty.