How Much Do House Extensions Cost in Greater London?

House extension prices can vary dramatically throughout the UK, influenced by the size of your plan, chosen materials, and build complexity. Industry data indicates that a single-storey rear extension may begin around £1,500 per square metre for a simple design, while standard builds often end up in the £1,800–£2,500 per square metre range. If you add complex steelwork, premium glazing, or luxurious finishes, costs can surpass £3,000 per square metre.

In Greater London, labour rates differ from one borough to another, but generally sit above national averages. If you’re in an outer borough, you might pay somewhat less than a Zone 1 location, enabling you to budget for better-quality fixtures or a more refined interior design. However, older or listed structures near conservation areas could require additional structural reinforcements, raising final totals. Large-scale expansions typically settle between £40,000 and £100,000+, while a narrower side-return extension might be cheaper, and multi-storey or high-end designs can exceed typical price bands if advanced engineering or premium materials feature. Should your scheme include a kitchen or bathroom, factor in the cost of plumbing, waterproofing, and electrics, which inflate expenditures.

When comparing quotes from builders, verify each includes foundation tasks, the structural envelope, roofing, fixtures, finishing, plus labour overhead. Also confirm if VAT—often 20%—is included or extra. While home-improvement outlets provide rough cost references, the most dependable figure emerges from obtaining multiple quotes from established firms and carefully comparing them line by line.

Different Types Of Extensions

There are also different requirements for different extensions. Under is a list of the different types of house extensions:

Side extensions
Single storey extensions
Extensions more than one storey

They each have their own specific limits concerning such as rear extensions requirements, height, roofing and windows. For extensions of more than one storey, there is for example a requirement that roof pitch must match the existing house as far as practicable.

Greater London

Greater London spans 32 boroughs plus the City of London, blending everything from Victorian terraces and 1930s semis to modern flats. Many homeowners choose single-storey rear expansions to create bigger kitchen-diners or unify living spaces. Others adopt side extensions if a side path or driveway exists, or loft conversions if building outward isn’t feasible. Some owners consider basements if extra floors aren’t an option, but this requires significant engineering. Each borough can have distinct local planning priorities—some might be more lenient, while conservation areas demand strict adherence to design guidelines.

Local contractors often advise scheduling skip deliveries and large drop-offs outside peak hours, given the city’s extensive traffic. Labour charges fluctuate across boroughs: from slightly lower in outlying zones to quite high in prime inner areas. Heritage buildings in older suburbs or districts near historical sites might need additional foundation or structural checks. The outcome of a well-executed extension is often both improved everyday usability and a rise in property value, especially near major transport links like the Tube or the Overground. Consulting neighbours early regarding party walls or shared boundaries helps circumvent disputes, which can be more likely in closely spaced London streets.

Whether you opt for a small single-storey extension that expands your kitchen or a grand multi-level addition for extra bedrooms, tailoring your plan to local conditions and regulations across Greater London is vital for quicker approvals and a harmonious final look.

Getting Started

Before starting, confirm the nature of the extension you need. Single-storey expansions can add a bright lounge or a spacious kitchen, while a double storey layout might provide both ground-floor and upstairs improvements. If you have a narrow side passage, you can exploit it for a wrap-around design. Alternatively, a loft or basement may allow extra levels, particularly if outward expansion isn’t feasible. Basements across Greater London can require major engineering, depending on borough rules and local geology.

Comprehensive planning in advance reduces potential obstacles mid-project. Develop a detailed budget by checking typical labour and material rates, and set aside contingency funds for refined finishes or unanticipated structural changes. If your design involves notable structural revisions, you might hire an architect or professional designer. Some building companies handle design-and-build, but generally request preliminary sketches or partial planning approvals for a precise quote. Many families in outer or inner London first consult an architect, then approach builders for formal estimates.

Securing a reliable contractor well ahead is prudent, as reputable firms book up quickly. Gathering quotes sooner lets you compare costs, contact references, and choose a contractor who aligns with your vision. An experienced team may propose refinements you hadn’t considered, like dividing an open space to add utility or repositioning doors for better flow.

Project Management

Most extensions follow one of two main organisational approaches:

• Single contract (design-and-build or main contractor)
  You sign a single agreement with a building firm that addresses all tasks—foundation excavation, structural framing, electrics, plumbing, roofing. They typically subcontract specialised trades, adding around a 10–15% markup. The advantage is a unified schedule and a single contact person if issues arise.
• Multi-trade or split contract
  You act as the project coordinator, employing separate trades for groundworks, bricklaying, roofing, plumbing, electrics, and so on. Although you may save on the main contractor’s overhead, you must juggle each trade’s schedule, ensuring materials arrive on time. If one trade misses a deadline, others might be stalled.

In Greater London, major or intricate expansions often lean toward a single-contractor method, especially for owners unable to supervise daily scheduling. If you do multi-trade, confirm you can commit enough time weekly to manage deliveries and watch progress.

Do I Need Planning Permission?

Whether you need planning permission hinges on your extension’s size, height, and placement on your property. Under Permitted Development Rights, you can sometimes enlarge your home without a formal planning application if your design remains within certain dimension and positioning constraints. If it overshoots them, you typically need to file a householder planning permission request.

Under are the general rules that apply to all extensions:
Only half the area of land around the "original house" can be covered by extensions or other buildings.
Extensions cannot be higher than the highest part of the existing roof; or higher at the eaves than the existing eaves.
Where the extension comes within two metres of the boundary the height at the eaves cannot exceed three metres.
Extension cannot be built forward of the ‘principal elevation’ or, where it fronts a highway, the ‘side elevation’.
The work cannot include:
verandas, balconies or raised platforms.
a microwave antenna (e.g. TV aerial or satellite dish).
a chimney, flue or soil and vent pipe.
any alteration to the roof of the existing house.
On Article 2(3) designated land the work cannot include cladding of the exterior.
The materials used in any exterior work must be of a similar appearance to those on the exterior of the existing house.
Source: Planning Portal.

Because Greater London is vast and diverse, with each borough having potential conservation areas, you must check with local planning authorities to see if you fit PD or require an application.

Do I Need Planning Permission For A New Storey?

Loft extensions that alter rooflines or add dormers frequently need planning permission. Still, adding a new storey can be allowed under permitted development if precise criteria are followed and you submit a prior approval request. Otherwise, Householder/Full Planning Permission is standard. If your house meets these conditions, the bullet points below outline the relevant restrictions:

Number of additional storeys:
One storey can be added to a single storey house
Two storeys can be added if the house has more than one storey.

Height increases:
The house cannot exceed 18 metres in total height
Each added storey cannot add more than 3.5 metres to the total height
If not detached (e.g. terrace or semi) the total height cannot be more than 3.5 metres higher than the next highest building that the house is attached to, adjoins, or is in the same row as.
The additional storeys must be constructed on the principal part of the house*
The additional storeys must not exceed 3 metres in height or the height of any existing storey in the principal part of the house (measured internally from floor to ceiling)
Engineering operations must only include works within the existing curtilage of the house to strengthen existing walls and foundations
The materials used must be of a similar appearance to those used in the construction of the exterior of the current house
Windows must not be placed in any wall or roof slope forming a side elevation of the house.

Further rules may apply once completed. In Greater London’s rows of terraces or semis, it’s important to confirm that an extra storey doesn’t stand out awkwardly or breach local building lines.

Do I Need Planning Permission For A New Basement?

Digging out a new basement typically needs planning permission, and substantial excavation under a property is likewise likely to require it because of the extent of the work. Meeting with your local authority early clarifies their criteria. Basement construction is inherently detailed, so even if formal planning consent isn’t always required, adherence to Building Regulations is crucial to guarantee structural soundness, safe escapes, ventilation, damp-proofing, fire standards, etc.

Always investigate potential local constraints. In certain pockets of Greater London, prior or area-specific planning conditions might override normal PD expansions. The local council’s guidance or consulting a planning advisor can confirm the feasibility of your basement plan.

Some property owners in areas with high land values or limited outward space do choose basements, though costs can jump due to advanced engineering near busy roads, party walls, or water courses.

Remember Building Regulations Application

Regardless of the size and shape of your extension, it must meet building regulations requirements. This is also regardless of whether you need planning permission or not.

You will need to submit a building regulations application. For smaller projects you can submit a Building notice but for larger extensions you’ll probably need a Full Plans Application. In this case full details of the proposed work will be submitted for approval before the work begins. With a Building Notice an inspector will inspect and approve the work as it is performed.

A Full Plans Application frequently flags potential design or safety flaws before building starts, while a Building Notice might suffice for smaller expansions. Each route concludes with building control confirming your extension aligns with code standards.

What’s The Difference Between Planning Permission And Building Regulations Application?

Whereas planning permission assesses whether the extensions meets local and national requirements, building control concerns structural safety and regulations compliance.

Even if your scheme passes under PD in Greater London, you still must seek building regulations sign-off to verify everything from foundation strength to adequate fire doors. With many older semis or terraces across the region, ensuring a robust structure is vital.

DIY Contribution

Homeowners sometimes consider tackling parts of an extension themselves. Painting, decorating, or landscaping can be good DIY tasks if you have the skills and time. Doing your own demolition, to an extent, can also be feasible—provided you understand which walls are load-bearing and follow safety precautions.

However, tasks such as electrical installation, gas connections, and structural changes almost always require qualified professionals. Mistakes in these areas can be costly and dangerous. Being realistic about your abilities is crucial; if you overcommit, you risk causing delays. Builders may need to pause until you finish a particular job, which can add to your final bill. If you’re determined to do some work yourself, consider hiring a professional for a consultation, as their input can help you avoid pitfalls.

Greater London owners often perform the finishing décor themselves to put a personal stamp on the space once the main build is final. Structural or mechanical roles typically remain with experts to maintain the schedule.

Do I Need An Architect?

If your layout is quite simple, you may rely on a structural engineer or building designer. Yet for bigger or more intricate expansions, an architect can be a huge asset. They merge practical considerations—flow, daylight, synergy with existing rooms—with design flair for a cohesive and pleasant environment.

They can also guide you on whether you’re within PD or should file a planning application. Although an architect’s cost adds to your initial outlay, it usually saves trouble by preventing design errors and producing a more refined outcome.

Greater London includes housing from classic Victorian terraces to new-build flats. An architect can unify older facades with modern expansions or add innovative features like roof lanterns or extended glazing that complement city living demands.

How Long Does It Take To Build An Extension?

A workable timeline ensures clarity throughout the build. A simpler single-storey rear extension—if permitted development, straightforward layout, and standard materials—might finish in weeks once construction begins. Larger expansions, multi-room or multi-floor, can stretch from several months to half a year or more, depending on complexity and trades required.

Occasionally, you might relocate temporarily if essential walls are taken down or if central services must be switched off. Even if you stay, dust, noise, and limited access to certain areas will likely be routine.

Keep a buffer for unpredictable delays. Wet or snowy weather might hamper outdoor tasks; inspectors may request small changes; deliveries can run late. Setting a realistic timetable with your contractor reduces stress, and finishing quicker than planned is always a plus. Likewise, a budget contingency can handle hidden structural tasks or changing design preferences mid-stream.

Throughout Greater London, traffic congestion might complicate skip drop-offs or deliveries, so choosing off-peak hours is wise. Large divergences from your original plan once building starts might push completion further out.

House Extensions Step By Step

Undertaking an extension is a major project, but with solid planning, skilled labour, and a properly allocated budget, it can be successful. Whether you envision a more open kitchen-lounge, new bedrooms, or a basement, it’s essential to grasp each stage and watch for potential pitfalls.

1. Start by confirming what you want to achieve—more natural light, a larger social area, or additional bedrooms.
2. Then decide how best to organise the project.
3. Check if you need planning permission and what kind of building regulations application you need to send in.
4. Gather quotes from at least three builders if possible, ensuring each has a solid track record and good references.
5. Check that their quotes are like-for-like in terms of scope.
6. Factor in the cost of planning applications, building control fees, and professional services such as architectural drawings or structural engineering.
7. Then develop a realistic schedule, communicate frequently with your chosen contractor, and keep a close eye on both time and budget.
8. Finally, as the build nears completion, consider a thorough inspection—often called a snagging survey—conducted alongside your main contractor or an independent professional. Address any shortfalls before final payment. Keep compliance certificates, warranties, and official approvals for any future remortgage or sale.

Once the new space is finalised and given approval, you can embrace a more practical living area. Whether you extended the ground floor for a family zone or built an extra upper storey, your property generally gains everyday convenience and potential resale appeal. Greater London owners especially profit if they are near good transport, schools, or job hubs. Conducting a snagging survey helps rectify small faults—like minor cracks or off-level doors—before the contractor closes out. Storing building control sign-offs and warranties also proves your extension was completed properly. With that, your newly enlarged Greater London home should cater to your changing requirements for years ahead.