More space, more light, more value — without moving. Our RIBA architects design extensions that transform how London homes function, while our in-house structural engineers and build teams deliver complete rear, kitchen, loft and basement projects on a fixed-price contract from foundation to final coat of paint.
London's housing stock was built for a different era. Victorian terraces, Edwardian semis and inter-war villas were designed around formal rooms, separate kitchens and service corridors — layouts that don't suit contemporary family life. A well-designed extension replaces cramped ground-floor space with a flowing, light-filled living area that connects the house to the garden and transforms daily life.
We focus on complete extension projects rather than small standalone packages: rear additions, kitchen-led extensions, loft conversions and basement conversions shaped around planning, structure, daylight, circulation and finished interiors.
Our integrated approach means one team handles every aspect: the RIBA architect designs the space, our structural engineers calculate the steelwork, our planning consultants navigate permitted development rules or conservation area restrictions, our RICS surveyors manage party wall matters, and our build team constructs the extension from foundation to final decoration. There's no coordination gap because there's no gap between firms.
Every extension starts with a free on-site consultation. We assess the site, discuss your brief, identify the planning route (permitted development or full application), check party wall implications and provide an honest budget indication — before any design fees are committed.
We organise extension work around premium project outcomes, with design, structure, approvals and construction managed by one senior team.
Full-width or partial-width extension to the rear of the property. The workhorse of London extensions — creating open-plan kitchen-diners with direct garden access.
Kitchen-led extensions for family homes, combining architecture, structure, glazing, services and finished interiors into one coordinated project.
Premium loft conversions delivered as part of the wider house extension strategy, with structure, stairs, daylight and finished rooms properly coordinated.
Lower-ground and basement projects for prime London homes, coordinated with engineering, waterproofing, party wall strategy and refined interior finishes.
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.
Kitchen-led extension work with structure, glazing, services, lighting and refined finishes coordinated around one complete ground-floor plan.
Full-width or partial rear extension with bi-fold doors to the garden. Creates a generous kitchen-diner-living space. 15–30 sqm added.
Premium loft conversion work with stairs, structure, roof glazing, insulation and finished bedroom or study accommodation coordinated together.
Basement and lower-ground projects planned around engineering, waterproofing, party wall strategy, light, ventilation and high-end interiors.
What separates a Hampstead Renovations extension 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.
RICS surveyors 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.
Kitchen-led extension creating a 38sqm open-plan kitchen-diner with roof glazing and full-width rear doors. Planning approved in conservation area.
Major rear extension creating an open-plan kitchen, improved upper-floor layout and refined family accommodation. Full planning permission secured through Haringey.
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Visit Hampstead On Demand →The ground-floor extension completely transformed our home. 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 larger extension in a conservation area. Hampstead Renovations designed the scheme 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.
A successful extension is not just extra floor area; it is the point where planning, structure, drainage, glazing and living space meet.
Hampstead Renovations coordinates extension projects from early feasibility through planning strategy, structural openings, steel design, drainage routes, glazing specification, party-wall sequencing, building-control information and the construction programme. That joined-up approach matters most where a rear or side-return extension changes the kitchen, dining and garden connection at the same time as altering load paths, roof drainage, neighbour interfaces and day-to-day access through the house.
Review the Fulham side-return extension case study for comparable proof, then read how our planning and conservation support and structural engineering service reduce design risk before work starts. If you are weighing scope, budget and timing, book an extension consultation with the team.
Extension case studies help you judge more than the finished floor area. They show the kind of planning, structure, glazing, drainage and kitchen-living decisions that should be resolved before a build starts. Begin with the Fulham side-return extension case study, then browse the wider case-study hub for other project contexts. The aim is to test how your own extension will connect old and new space, manage neighbour interfaces and avoid late design changes once structural openings are under way. If you want to discuss a rear, side-return or wrap-around extension, contact Hampstead Renovations with the property type and early brief.
Everything London homeowners ask about house extensions.
We visit your property, assess the site, discuss your brief and give you an honest feasibility assessment — including extension type, budget, timeline and planning route. No obligation.
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