Architects, Engineers, Surveyors & Builders Under One Roof.
Surveyor-led refurbishment advice via Hampstead Chartered Surveyors →One Studio. One Contract. One Team.
We deliver Belgravia mansion block refurbishment with architects, engineers, surveyors and builders under one fixed-price contract - design, technical coordination, procurement, directly managed site teams, Building Control, programme control and final handover through one accountable team.
Belgravia's mansion blocks — Eaton Square, Belgrave Square, Grosvenor Crescent, Eaton Place, and the dozens of named blocks (Greville House, Thorburn House, Bolbec House, Carlton Lodge, Royal Court House) — are almost entirely held under long leases with freeholders that include Grosvenor Estate, Eaton Square Estate, or specific block trustees. Every alteration requires multiple layers of consent that don't apply to freehold property.
The practical reality: you cannot move a radiator without landlord approval. You cannot knock through a wall without a licence for alterations. You cannot core-drill the floor slab without a surveyor's report and freeholder consent. Plumbing modifications route through shared risers that serve multiple flats. Noise windows restrict works to specified hours. Delivery access often requires pre-booked porter support.
Our track record: six documented refurbishments across four Belgravia mansion blocks (Greville House ×2, Thorburn House ×2, Bolbec House, Carlton Lodge). We know the managing agents, the freeholder consent process, and the practical workarounds that keep programmes on track.
Westminster · SW1X
Any structural change, plumbing move, flooring replacement or electrical rewire requires formal licence from the freeholder or managing agent. Documentation typically required: drawings, method statements, contractor insurance proof (our £10M cover meets all Belgravia requirements), programme.
Savills, Knight Frank Block Management, and estate-specific agents run operational compliance. We liaise weekly, submit RAMS, coordinate delivery slots, and ensure porters are pre-notified.
For blocks held on Grosvenor leases, a separate licence from the Estate's surveyors is often required in addition to the block freeholder. We have standing relationships and know what Grosvenor approves vs refuses.
Typical Belgravia restrictions: no noisy works before 9am, after 5pm, or on weekends. We plan demolition and structural works within these windows and use low-noise methods where possible.
Six documented refurbishments across four Belgravia mansion blocks. View our Belgravia projects →
Westminster · SW1X
A different discipline from house renovation. Our RIBA architects and IStructE engineers prepare the licence submissions, our RICS-regulated surveyors run the managing agent liaison, and our directly-employed trades deliver the build under strict Belgravia noise windows and service riser constraints. One fixed-price design-build contract covering freeholder consent, Grosvenor Estate licence, Westminster planning where external, and the full refurbishment through to handover.
A mansion block refurbishment in Belgravia is not a house renovation moved indoors. Eaton Square, Belgrave Square, Grosvenor Crescent and Eaton Place are populated by purpose-built Victorian and Edwardian mansion blocks — Greville House, Thorburn House, Bolbec House, Carlton Lodge, Royal Court House — sitting on long leases with Grosvenor Estate or block-specific trustees. The regulatory surface area is different, and the operational constraints are different.
The difference begins with consent. Before a single tile is lifted, the leaseholder needs a licence for alterations from the freeholder, a separate Grosvenor Estate licence where the block sits on a Grosvenor lease, managing agent approval of method statements and RAMS, and proof of contractor insurance meeting the block's threshold (our £10M PI/PL meets every Belgravia requirement we've encountered). Structural changes additionally require IStructE-stamped engineering drawings and, where party walls are in play, a Section 6 award.
The difference continues on site. Works hours are typically 9am to 5pm Monday to Friday — no early starts, no evenings, no weekends. Deliveries must be pre-booked with the head porter. Core drilling of floor slabs requires dust suppression and scheduled slots because neighbours are resident above and below. Plumbing modifications route through shared service risers, which means coordination with the block's communal systems, not just the flat you're working in.
Our Belgravia track record covers eight documented projects across four mansion blocks: two flats at Greville House, two at Thorburn House, Bolbec House, and the penthouse duplex at Carlton Lodge. We know Savills and Knight Frank Block Management contacts by name. We know which Grosvenor Estate surveyors respond fastest. We know which parts of which lease clauses trip up contractors who don't refurbish mansion blocks regularly. That institutional knowledge turns a 6-month regulatory obstacle course into a managed, predictable programme.
Six documented refurbishments across four Belgravia mansion blocks. Each links through to the full case study with scope, programme, and regulatory context.
Full refurbishment of a 3-bed mansion flat. Kitchen, bathrooms, joinery, rewire, replaster — delivered under freeholder licence with weekly managing agent reporting.
View case study →Kitchen and principal bathroom renovation with plumbing relocation through shared risers. Works programmed around resident neighbours above and below under strict 9–5 noise windows.
View case study →Full refurbishment with structural wall removal between reception and dining. IStructE engineering drawings, freeholder licence and Section 20 consultation.
View case study →Kitchen replacement, two bathrooms, bespoke joinery throughout. Programmed to run alongside occupation in one wing via phased handover under managing agent supervision.
View case study →Full refurbishment of a mansion flat including heritage cornicing restoration and sympathetic period joinery. Delivered under Grosvenor Estate licence with conservation-aware material specification.
View case study →Penthouse duplex refurbishment including internal staircase reconstruction, new kitchen, three bathrooms and roof terrace upgrades. Vacant possession, full programme with licensed external works.
View case study →Many house extensions can be built without planning permission under Permitted Development (PD). Here are the key rules for London homeowners.
Single-storey rear extensions: Up to 3 metres deep on attached houses (terraced and semi-detached) or 4 metres deep on detached houses, measured from the original rear wall. The extension must not exceed 4 metres in height and the eaves must not be higher than the existing eaves. These limits apply without any notification to the council.
Prior Notification (Larger Home Extension) scheme: Extends the PD limits to 6 metres (attached) or 8 metres (detached) for single-storey rear extensions. You must notify the council and your immediate neighbours before starting. The council has 42 days to determine whether prior approval is needed based on the impact on neighbours' amenity. If no response is received within 42 days, you may proceed.
Side extensions: A single-storey side extension must not exceed half the width of the original house. It must be no more than 4 metres in height and the eaves must match the existing. Materials should be similar in appearance to the original house.
Two-storey extensions: Permitted under PD up to a maximum 3-metre depth from the rear wall. Must not be within 7 metres of the rear boundary. The roof pitch must match the existing house. Cannot extend beyond the side wall of the original house.
Forward of the principal elevation: Extensions cannot project forward of the principal (front) elevation facing a highway. This is an absolute rule under PD with no exceptions.
Conservation area restrictions: Properties in conservation areas lose PD rights for side extensions and rear extensions visible from a public highway. Cladding the exterior and adding dormers on roof slopes facing the highway are also restricted. Article 4 directions can remove additional PD rights entirely. Always check your specific property's designations before assuming PD applies.
Extensions affect your neighbours. Understanding the legal framework protects both your project and your relationship with those next door.
The Party Wall etc. Act 1996 applies when your extension foundations are within 3 metres of a neighbouring building's wall — which covers virtually all terraced and semi-detached extensions. If your foundations go deeper than your neighbour's (common with basement-level extensions), the 6-metre rule applies instead. You must serve notice at least 2 months before work starts. We handle the entire process in-house at no additional cost.
Two-storey extensions can reduce daylight and sunlight to neighbouring windows. While the planning system considers amenity impact, the common law right to light is a separate legal issue. A neighbour can seek an injunction to prevent or remove a building that substantially reduces the light to their windows — even if planning permission was granted. For two-storey extensions near boundaries, we commission daylight/sunlight assessments (BRE guidelines) to quantify the impact and demonstrate compliance.
If your extension is built up to or astride the boundary line, a different type of party wall notice is required. Building astride the boundary (where the wall sits partly on each property) requires your neighbour's written consent. Building up to the boundary (entirely on your land) does not require consent but still requires notice. The position of the boundary — and the ownership of any existing boundary wall — should be confirmed before design work begins.
If you apply for planning permission, neighbours are notified and can submit comments during the consultation period (typically 21 days). Objections are considered by the planning officer but do not automatically prevent approval. Common objection grounds include loss of light, overlooking, noise and visual impact. Our applications pre-emptively address these concerns with detailed design justification, reducing the risk that objections influence the outcome.
Every extension requires building regulations approval — separate from planning permission. Here are the key Parts that affect house extensions in London.
The most impactful regulation for extensions. New walls, roofs, floors and glazing must achieve minimum U-values: walls 0.28 W/m2K, flat roofs 0.18 W/m2K, floors 0.22 W/m2K, windows 1.6 W/m2K. Extensions over 25% of the existing floor area may require SAP calculations to demonstrate whole-building energy performance. This typically means high-performance insulation and double or triple glazing as standard.
Extensions built within 1 metre of the boundary must have fire-resistant external walls (typically 1-hour fire rating). Windows and openings facing the boundary are restricted. If the extension creates a new habitable room above ground floor level, fire escape provisions must be considered — including window sizes and fire doors to the escape route.
Where an extension creates a new bedroom that shares a wall or floor with a room in an adjoining property, acoustic separation must meet minimum standards. This is particularly relevant for two-storey extensions on terraced houses where the new first-floor room shares a party wall with the neighbour's bedroom. Sound insulation testing may be required.
New ground floor extensions must have level or ramped thresholds (maximum 15mm upstand) at external doors to allow wheelchair access. Internal door openings should be minimum 775mm clear width. This regulation applies to all new extensions regardless of whether the occupants currently need accessible features — the building must be usable by future occupants.
SAP calculations: For larger extensions, a Standard Assessment Procedure (SAP) calculation may be required to demonstrate that the extension meets the energy targets set by Part L. We commission these calculations as part of the building regulations package and submit them alongside the structural and architectural drawings. The cost is typically £300–£500 and is included in our design-and-build projects.
A clear, structured process that takes the uncertainty out of extending your home.
We visit your property, measure the site, assess the garden, check party wall situations and discuss your brief in detail. We identify whether your extension falls within permitted development rights or requires planning permission, and flag any conservation area, Article 4 or tree preservation order constraints. You receive a written feasibility assessment with an indicative budget and recommended approach within 48 hours.
Our architects produce the extension layout with 3D visualisations. Structural engineers design the steelwork, foundations and connection details. We submit planning applications or lawful development certificates, building regulations packages and party wall notices in parallel. For design-and-build projects, the kitchen design, lighting scheme and material selections run concurrently so everything is resolved before construction starts.
Foundations are excavated and poured (typically strip or trench-fill), walls built to DPC level, floor slab laid and the structural shell erected — blockwork walls, steel beams, lintels and the roof structure. The opening between the existing house and the new extension is formed, with temporary propping supporting the existing structure until the steel beam is in position. Once the roof is weathertight, the extension is sealed and internal works begin.
Insulation, plasterboarding, first fix electrics and plumbing, underfloor heating, window and door installation, kitchen fit-out, tiling, flooring, second fix carpentry, painting and decoration. Bi-fold or sliding doors are installed connecting the extension to the garden. External works — patio, drainage, landscaping — complete the project. Building control conducts the final inspection and issues the completion certificate.
Guide prices for London house extensions. All prices are fixed and include design, engineering, planning, full build and decoration.
Infilling the side alley with a glazed roof. Doubles kitchen width and creates a bright, open-plan ground floor. 8–15 sqm added.
Full-width or partial rear extension with bi-fold doors to the garden. Creates a generous kitchen-diner-living space. 15–30 sqm added.
Combined rear and side extension creating an L-shaped addition. The largest single-storey extension option. 25–45 sqm added.
Two-storey extension — kitchen below, bedroom or bathroom above. Best sqm/cost ratio but requires full planning permission. 30–60 sqm total.
What separates a Hampstead Renovations refurbishment from a standard builder's quote.
Every extension is designed by a RIBA architect to suit your specific house, site and lifestyle. No templates, no catalogue layouts — a bespoke design that maximises light, space and the connection between your home and garden.
Architects, structural engineers, planning consultants, party wall surveyors and build teams all under one roof. No subcontracted design, no outsourced engineering, no coordination gaps between separate firms. One team, one contract, one accountable party.
The price we quote is the price you pay. Not an estimate with provisional sums. Not a price that escalates when you choose your fixtures. A fixed, agreed total covering design, engineering, the full build and every material specified in the contract.
We've secured planning approvals across every inner London borough — including conservation areas in Camden, Islington, Westminster and Haringey with the most restrictive policies.
We maximise what can be achieved under PD rights — including the larger home extension scheme (up to 6m rear on terraces, 8m on detached) — avoiding planning costs and delays where possible.
Structural glass roofs, frameless glass corners, slim-profile aluminium bi-folds and floor-to-ceiling fixed glass. We design extensions that flood the ground floor with natural light.
Most extensions are kitchen-led. Our kitchen designers work alongside the architect from day one, ensuring the kitchen layout, island position and appliance locations drive the extension geometry — not the other way round.
Surveying support through Hampstead Chartered Surveyors can handle all party wall notices and agreements in-house. For terraced and semi-detached extensions, party walls are always a factor — our experience streamlines the process.
We install wet or electric underfloor heating beneath extension floors as standard on most projects — eliminating radiators and freeing up wall space in the new room.
In sensitive settings, we design extensions that satisfy conservation officers — using appropriate materials, roof forms and detailing that complement the existing building's character.
Patio, drainage, garden reinstatement and boundary work are part of the fixed-price contract — not treated as extras that inflate the final bill after the extension is built.
Selected house extensions completed by our team across London.
6m full-width rear extension with structural glass roof and 4m bi-fold doors. Open-plan kitchen-diner with island under permitted development.
L-shaped wraparound creating 38sqm open-plan kitchen-diner with glazed side return and full-width rear doors. Planning approved in conservation area.
Two-storey rear extension — open-plan kitchen below, master bedroom with en-suite above. Full planning permission secured through Haringey.
Need a same-day repair or maintenance visit in NW London?
Visit Hampstead On Demand →The side-return extension completely transformed our ground floor. What was a dark, narrow kitchen is now a bright, open-plan room with a huge skylight running the full length. The architect suggested the glazed corner detail that everyone comments on — that's the difference between a design-and-build firm and a standard builder's extension.
We were worried about getting planning for a wraparound in a conservation area. Hampstead Renovations designed an extension with zinc cladding and a recessed glass link that the conservation officer praised as exemplary. The build was immaculate and the fixed price held exactly — not a single extra charge in 14 weeks of construction.
Having the kitchen designer, architect and structural engineer all working together from the start meant our extension was designed around our kitchen — not the other way round. The island position, the sink location, the pendant lighting — everything was resolved before the builders dug the foundations. No compromises, no changes on site.
Everything London homeowners ask about house extensions.
Use these area-specific guide pages to compare the next build routes, planning questions and cost topics people commonly research in Hampstead NW3.
We visit your property, assess the site, discuss your brief and give you an honest feasibility assessment — including scope, managing agent coordination, Grosvenor Estate licence timeline and indicative budget. No obligation.
We visit your Belgravia flat, review the lease and building constraints, and provide a clear written assessment of scope, consents required, and indicative timeline — completely free.
Book Free ConsultationWe're not a national chain — we're a local design and build practice with deep roots in Hampstead and the surrounding neighbourhoods.
Our design studio at 250 Finchley Road NW3 is just 2 minutes from Hampstead. Visit to see materials, meet the team, and discuss your project in person.
Our RIBA architects have extensive experience with Camden Council's planning department, conservation officers, and building control team. We know what gets approved.
From the Georgian townhouses, Victorian villas, Edwardian mansions and listed buildings on Church Row, Flask Walk, Frognal, Downshire Hill and Keats Grove — we understand the specific construction challenges and planning context of every property type in NW3.