An extension isn't just extra square metres.
It's a chance to fix how your house
works.
Most London terraces and semis were designed for a different era. Small kitchens cut off from the living room. Dark hallways. Cramped dining areas. An extension lets you reorganise the ground floor — opening up the back of the house to light, connecting the kitchen to the garden, and creating the kind of space your family actually needs.
We handle everything: architectural drawings, structural engineering, planning applications (or permitted development confirmation), building control, groundworks, steelwork, roofing, glazing, M&E, decoration, and landscaping. One contract, one project manager, one team on site.
We've built extensions in conservation areas, on listed buildings, on party-wall-constrained terraces, and on sites with difficult access. If you're in NW3, NW6, NW1, NW8 or NW5, we've almost certainly worked on your street.
Five ways to extend your home
Each type suits different properties, different budgets, and different planning contexts. Here's what's possible.
Single-Storey Rear Extension
The classic London extension. Push out the back of the house by 3–6 metres, install bi-fold or sliding doors, and create an open-plan kitchen-diner that connects to the garden. Under permitted development, you can extend up to 6m (detached) or 3m (terrace) without planning permission — subject to a prior approval notification.
Side-Return Extension
That narrow alley down the side of your house? It's wasted space. A side-return extension fills it in, typically adding 2–3 metres of width to your kitchen. Combined with a rear extension, it creates an L-shaped or wrap-around layout that transforms the entire ground floor. Ideal for Victorian terraces.
Wrap-Around Extension
A combination of rear and side-return extensions that maximises your ground-floor footprint. The result is a single, expansive open-plan space — often 40–60 sqm of connected kitchen, dining and living area. Usually requires a planning application, but we have a 98% approval rate across Camden.
Double-Storey Extension
If you need both more living space and an extra bedroom or bathroom, a two-storey extension delivers both in a single build. Ground floor for kitchen/dining, first floor for bedroom, en-suite and storage. Always requires a full planning application.
Garden Room & Outbuilding
A standalone structure in the garden — home office, studio, gym, or guest accommodation. Typically a timber-framed, fully insulated building with power, heating and lighting. Most garden rooms under 15 sqm and 2.5m eaves height don't need planning permission.
Do you need planning permission?
It depends on the size, position and context of your extension. Here's the quick version — we handle the detail.
Permitted Development (No Application)
Many single-storey rear extensions can be built under Permitted Development rights — no planning application needed. You still need Building Regulations approval.
- Rear extension up to 3m (terrace/semi)
- Rear extension up to 4m (detached)
- Maximum eaves height 3m
- Not in front of the principal elevation
- No more than 50% of curtilage covered
- Not on listed buildings or in AONBs
Prior Approval (Larger Home Extension)
Under the "Larger Home Extension" scheme, you can extend further — but must notify the council, who consult your neighbours. Decision in 42 days.
- Rear extension up to 6m (terrace/semi)
- Rear extension up to 8m (detached)
- Single storey only
- Neighbour notification required
- 42-day decision period
- Free to apply in most boroughs
Full Planning Application
Required for double-storey extensions, wrap-arounds that exceed PD limits, side extensions on restricted plots, and most work in conservation areas.
- Architectural drawings required
- Design & Access Statement
- 8-week decision target
- We manage the entire process
- 98% approval rate (Camden)
- Pre-app advice available
Conservation Areas & Listed Buildings
Permitted Development rights are restricted in conservation areas. Listed buildings need Listed Building Consent for any alteration. We work with heritage consultants where needed.
- PD rights may be removed (Article 4)
- Materials must match existing
- Design sensitivity required
- Heritage Impact Assessment
- We know Camden's conservation officers
- Proven track record in CA applications
"Ross and his team handled everything — planning, structural engineering, building control — and delivered a beautiful rear extension that completely transformed how we use our ground floor. We finally have the kitchen we always wanted."James Ward, Investment DirectorResidential Portfolio, NW3
From first call to moving the furniture in
A typical extension takes 12–20 weeks on site. Here's what happens at each stage.
Site Survey & Feasibility
We visit, measure the property, discuss what you want, and assess what's possible under permitted development or planning. You get an initial budget range and timeline within a week.
Architectural Design & Planning
Our architects produce floor plans, elevations and 3D visuals. If planning permission is needed, we submit the application and manage the process through to approval. Structural engineer engaged in parallel.
Fixed-Price Contract & Mobilisation
Detailed specification, fixed-price contract, and programme issued. Party wall agreements arranged where needed. Skip and scaffold booked. Materials ordered.
Groundworks & Structure
Foundations dug and poured. Steelwork installed. Walls built in block or timber frame. Roof structure formed and weathertight. This is the heaviest phase — typically 4–6 weeks.
First Fix, Glazing & Services
Windows and doors fitted. Electrics, plumbing and heating first-fixed. Insulation installed. Internal walls plastered. Underfloor heating laid if specified. The interior takes shape.
Fit-Out, Decoration & Handover
Kitchen installed. Flooring laid. Second-fix electrics and plumbing completed. Decoration throughout. Building control final inspection. Professional clean. Keys handed over with compliance certificates and 5-year warranty.
Extensions we've designed and built
2 Holland Avenue, Wimbledon SW19
Full three-phase extension programme: loft conversion with dormer, two-storey rear extension, and single-storey side extension — combined with a complete internal refurbishment. The ground floor was opened up into a 55 sqm kitchen-living-dining space with level access to the garden.
Victorian Terrace, Hampstead NW3
Single-storey rear extension with full-width glazed bi-fold doors to the garden, combined with a mansard loft conversion. The ground floor was completely reconfigured — WC relocated, utility room created, and a 32 sqm open-plan kitchen-diner installed with premium finishes throughout.
Camden High Street, NW1
Mixed-use project combining a rear extension for the ground-floor commercial unit with upper-floor residential refurbishment. Structural steel package throughout, new roof, and full services renewal — all within Camden's strict planning framework.
What does an extension cost?
Realistic ranges for North West London based on recent projects. We provide fixed prices after surveying your property.
| Extension Type | Typical Range |
|---|---|
| Single-storey rear extension (standard spec) | £2,500 – £3,500/sqm |
| Single-storey rear extension (premium spec) | £3,500 – £4,500/sqm |
| Side-return infill extension | £2,800 – £3,800/sqm |
| Wrap-around (rear + side combined) | £2,800 – £4,000/sqm |
| Double-storey rear extension | £2,500 – £3,500/sqm |
| Garden room / outbuilding | £1,800 – £3,000/sqm |
| Premium bi-fold / sliding doors (per set) | £3,000 – £8,000 |
| Architectural design + planning application | £3,000 – £6,000 |
All prices exclude VAT. Includes foundations, structure, roofing, glazing, electrics, plumbing, plastering and decoration. Kitchen and flooring quoted separately.
"A company where you get value for your money while at the same time achieving excellent quality. Their work is carried out on time and within budget. We've worked with them on multiple projects and they never disappoint."Brian Ingham, DirectorGreen Evolution Limited
Extension FAQ
Under Permitted Development, you can typically extend 3m to the rear (terraced/semi) or 4m (detached) without an application. Under the Larger Home Extension scheme, this increases to 6m and 8m respectively — but you must notify the council and wait 42 days. Side extensions up to half the width of the house are also possible under PD, subject to conditions.
A single-storey rear extension typically takes 10–14 weeks on site. Add 6–10 weeks for design and planning beforehand. A wrap-around is 14–20 weeks on site. A double-storey extension is 16–24 weeks. We provide a firm programme before work starts.
If your extension is built up to or on the boundary with a neighbour, yes — you'll need a Party Wall Agreement under the Party Wall Act 1996. We arrange the party wall surveyor and manage the process. Typical cost is £700–£1,200 per neighbour.
Yes, for almost all extensions. It's noisy and dusty at times — especially during groundworks and demolition — but the house remains habitable. We seal off the work area with temporary partitions and dust sheets. Plumbing and electrics are maintained throughout.
We introduce ourselves to neighbours before work starts, provide contact details, and manage deliveries and noise to minimise disruption. If a planning application is needed, neighbours are formally consulted by the council. We can also discuss designs with neighbours proactively to smooth the process.
In most cases, yes. A well-designed rear extension in North West London typically adds £50,000–£150,000 to the property value — significantly more than the build cost. The best return comes from extensions that create open-plan kitchen-living-dining spaces with good garden connections.
Everything in the specification: foundations, structural steelwork, blockwork, roofing, glazing (windows and doors), electrics, plumbing, heating, insulation, plastering, decoration, and project management. Skip hire and scaffolding included. We include a 10% contingency — unused contingency is not charged. Kitchen and flooring are quoted separately so you can choose your own specification.
Find your local extension page
Let's talk about your extension
Book a free site visit. We'll measure your property, discuss what you want to achieve, check your permitted development rights, and give you a realistic budget and timeline — no obligation.
Unit 3, Palace Court, 250 Finchley Road, Hampstead, London NW3 6DN
Mon–Fri 9am–8pm · Saturday 9am–6pm · Sunday by appointment
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