House
extensions
in Hampstead, NW3
Architects, Engineers, Surveyors & Builders Under One Roof.
One Studio. One Contract. One Team.
RICS surveying support for party walls, licence to alter, conservation-area works & neighbour mattersWe design and build Hampstead house extensions across Church Row, Flask Walk, Heath Street - side-return, rear, wraparound and double-storey additions for Georgian and Victorian villas, Period terraces and larger family homes where planning strategy, conservation detailing, Party Wall sequencing and structural engineering need handling properly.
House Extensions in Hampstead: What You Need to Know
Every house extension project in Hampstead is designed to respect the Hampstead Conservation Area and the character of Georgian & Victorian villas, period terraces, mansion flats. Our in-house RIBA Chartered Architects handle Camden planning applications, our chartered structural engineers specify any load-bearing work, and our directly-employed trades deliver the build under one fixed-price contract. We coordinate Building Control, Party Wall awards where needed, and all certifications through to handover.
Hampstead's conservation area status means extensions must be sensitively designed. Camden expects extensions to use matching or complementary materials and to respect the scale and character of the original building. We navigate these requirements daily.
London's most prestigious village with Flask Walk, Church Row, and Frognal. Camden conservation area with strict planning controls. Home to listed buildings, heritage pubs, and the Heath. Side-return extensions are particularly popular in Hampstead's terraced streets, transforming narrow kitchen spaces into full-width open-plan living areas connected to the garden.
Because so much of NW3 lies within the Hampstead Conservation Area, permitted-development rights are frequently restricted, so most Hampstead extensions need a full householder planning application to Camden rather than a Lawful Development Certificate. The many statutory-listed houses around Church Row, Frognal and Downshire Hill also require Listed Building Consent, and Camden's conservation officers expect extensions to use London stock brick, timber sliding-sash windows and natural slate that respect the original building.
The kind of extension that works is set by the property itself. On the Victorian terraces off Flask Walk and toward South End Green, the side-return extension is the signature Hampstead project — opening a narrow galley kitchen into a full-width kitchen-diner that connects to the garden. The larger Georgian and early-Victorian villas around Frognal and Downshire Hill suit a carefully-scaled single-storey rear or garden-room addition, while in mansion flats and period conversions “extending” usually means internal reconfiguration, as external additions are rarely consentable.
Two local factors catch Hampstead owners out. The village is built on the hill rising to the Heath, so split levels, retaining structures and right-to-light and Party Wall issues with stepped neighbours are common — we plan the structure and any Party Wall awards from the first design. And homes backing onto Hampstead Heath or adjoining Metropolitan Open Land face additional protection of views and openness, which shapes how far into the garden you can build.
Local character & heritage: extending in Hampstead
Hampstead's character spans three centuries of architecture. The Georgian heart around Church Row, Admiral's House and Burgh House gives way to the grand Victorian villas of Fitzjohn's Avenue and the Italianate terraces climbing toward the Heath, and then to two of Britain's most important modernist buildings — Erno Goldfinger's 2 Willow Road and the Bauhaus-influenced Isokon (Lawn Road) flats. Few London villages pack so many protected periods into so few streets.
That mix is exactly why extending in Hampstead is a design problem before it is a building one. Camden's conservation officers judge an addition behind a Georgian terrace on Church Row by completely different criteria to one beside a 1930s modernist house or a Victorian villa on Rosslyn Hill. Materials — London stock brick, natural slate, timber sash windows — scale, and the relationship to the original roofline all have to be argued case by case, and the large number of statutory-listed houses adds Listed Building Consent on top of planning.
In practice the winning Hampstead projects are the well-judged ones: a side-return that opens a narrow terraced kitchen to the garden, a single-storey rear addition to a villa that sits quietly below the original eaves, or a sensitive internal remodelling of a mansion flat. We design every Hampstead extension from the first sketch to satisfy the conservation officer — because here, that is the difference between consent and refusal.
Hampstead heritage & architecture: Church Row · Admiral's House · Burgh House · 2 Willow Road · the Isokon Building · Fitzjohn's Avenue
Extending in Hampstead is a consenting exercise before it is a building one. Practically the whole district lies within the Hampstead Conservation Area; Article 4 directions have removed many of the permitted-development rights an owner elsewhere would rely on, and Camden pays close attention to windows, roofs, rear elevations and basements — precisely the elements a house extension touches.
The approvals then stack by tenure and status. Many of the grand houses are Grade II listed — making a Hampstead scheme as much about consent and coordination as about construction — and in a listed building, consent is needed for internal change as well as external. Where the property is a leasehold flat, a Licence to Alter runs alongside Camden's decisions. From the Georgian houses by Church Row to the villas of Fitzjohns Avenue and Netherhall Gardens, the stock varies street by street, and the consent route varies with it.
The build itself answers to the village: restricted access on narrow streets, party-wall awards between closely-packed houses and the basement engineering many schemes involve drive the budget more than floor area does. As headline ranges excluding VAT, a single-storey rear extension in Camden runs £71,250–£112,500, with a side return at £90,000–£120,000 as a London-wide band.
House Extensions in Hampstead: Applied to the Local Stock
Almost all of Hampstead sits within the Hampstead Conservation Area, with Article 4 directions removing many permitted-development rights. London-wide cost band for rear extension — single storey: £71,250–£112,500 excluding VAT (Resi rear extension cost guide, Oct 2025).
Sources: Camden Council - Article 4 Directions: heritage and conservation (2026); Rear extension — single storey (Resi rear extension cost guide, Oct 2025) (2026)
What a House Extension Involves
An extension reshapes how the whole ground floor works, not just how big it is — the new structure, the opening into the existing house, the kitchen and the garden connection all have to be designed as one move. We take each project from feasibility drawings through consents, structure and fit-out under a single fixed-price contract. Most extensions we build include the scope below.
- Rear extensions — single-storey additions that open the back of the house to the garden
- Side-return & wraparound — infilling the side alley of a terrace, alone or combined with a rear addition
- Double-storey — new bedrooms or bathrooms above the ground-floor addition, designed to sit comfortably with the original roofline
- Foundations & steel — groundworks, beams and the opening into the existing house, engineered by our own structural team
- Glazing — rooflights, glazed roofs and slim-framed sliding or bi-fold doors specified for light and thermal performance
- Kitchen integration — the kitchen layout planned with the architecture from the first drawing, not squeezed in afterwards
- Services & heating — electrics, plumbing, drainage and underfloor heating built into the new floor
- External works — patio, drainage connections and garden reinstatement completed within the contract
How We Run Your Project
Six stages, with the consents and engineering settled before the first spade goes in.
- Feasibility visit — we assess the site, the boundaries and your brief, and identify the right consent route for your property.
- Design & approvals — our architects draw the scheme while planning or permitted development paperwork, structural calculations and party wall notices progress together.
- Fixed-price contract — every element specified and priced before construction, from foundations to door hardware.
- Groundworks & shell — excavation, foundations, walls, steel and roof, taken to weathertight while you carry on living in the house.
- Fit-out — insulation, services, glazing, kitchen, flooring and decoration, with the opening into the existing house formed once the shell is sealed.
- Completion — building control inspection, snagging, external works and handover with the full certification pack.
Read the full house extension guide for extension types, permitted development limits and the build programme stage by stage.
Many rear extensions can proceed under permitted development — broadly up to 3m deep on attached houses and 4m on detached, extendable to 6m and 8m through the prior approval scheme — but conservation areas, Article 4 directions and listed status change the picture, and every extension needs Building Regulations approval regardless of the planning route. Where foundations come within 3m of a neighbouring building, the Party Wall etc. Act 1996 obliges you to give adjoining owners a minimum of two months’ written notice before construction can begin. Our planning guide library sets out the rules for each borough.
Why Hampstead Renovations
We hold £10 million public liability insurance with Aviva; the certificate is available on request.
House Extensions in Hampstead: Questions
Can I extend my house in Hampstead under permitted development?
Usually not. Almost all of Hampstead sits within the Hampstead Conservation Area, and Article 4 directions have stripped out many permitted-development rights — so most Hampstead extensions proceed by way of a full planning application, judged on conservation terms from the start.
What is distinctive about extending a house in Hampstead?
The building always comes first. From the Georgian and early-Victorian houses around Church Row to the Victorian villas of Fitzjohns Avenue and Netherhall Gardens, the stock changes street by street — and listed properties add Listed Building Consent, with leasehold flats needing a Licence to Alter, on top of any Camden approvals for the extension itself.
Our Hampstead house is listed — can we still extend it?
Listing changes the process, not necessarily the answer. Many of Hampstead's grand houses are Grade II listed, which makes the project as much about consent and coordination as about building — and in a listed property, consent is required for internal alterations as well as external ones, so the extension and any knock-through it implies are designed for the heritage case from the very start.
Can we pair a rear extension with a basement in Hampstead?
Plenty of NW3 schemes do — basement engineering is one of the characteristic components of a Hampstead budget — but Camden watches basements as closely as it watches rear elevations, and the excavation itself is substantial work: London-wide guidance puts new excavation and underpinning at £2,100–£4,000 per square metre of excavated area, excluding full fit-out. We appraise the combined scheme honestly before recommending it.
How much does a house extension cost in Hampstead, NW3?
House extensions in Hampstead typically cost £2,800–£4,500/sqm. A single-storey rear extension runs approximately £69,000–£115,000, while a double-storey extension costs £115,000–£207,000. Our fixed-price contracts include foundations, structural steelwork, full build and interior fit-out.
Recent Projects Near Hampstead
Book a Free Consultation
Visit our studio or invite us to survey your home. We’ll assess scope, discuss design possibilities and provide an honest budget framework — completely free.
Free Consultation
We survey your property, discuss your vision and provide a clear budget framework.