How Much Do House Extensions Cost?

Extension prices in the UK can fluctuate widely due to multiple factors, including design scope, material specifications, and structural requirements. Industry data commonly references that a single-storey rear extension starts near £1,500 per square metre for a simpler build, while many standard expansions occupy the £1,800–£2,500 per square metre bracket. If you opt for intricate steel frameworks, designer glass, or high-end interior selections, costs might push over £3,000 per square metre.

In Wandsworth, a southwest London borough encompassing areas like Clapham Junction (straddling Wandsworth and Lambeth), Battersea, Putney, Wandsworth Town, and Tooting, labour fees generally rank moderate to high. It’s a highly sought-after zone with a mix of Victorian terraces, Edwardian homes, 1930s semis, and modern riverside developments near the Thames. If your property is an older Victorian house near Earlsfield or a 20th-century semidetached in Balham, you may face extra structural tasks—like underpinning or advanced damp-proofing—driving up the final bill. Larger expansions typically cost in the £40,000–£100,000+ zone, while smaller single-storey or side-return additions might land cheaper. Big multi-level or particularly luxurious expansions surpass standard cost levels if advanced engineering or bespoke finishes are essential. If you add a new or relocated kitchen or bathroom, you’ll need more plumbing, wiring, and waterproofing, inflating costs further.

When requesting quotes from building firms, be sure each covers foundation excavation, structural work, roofing, fittings, finishing, labour overhead, etc. Also clarify if VAT—commonly 20%—is part of the total or extra. While renovation magazines or home-improvement sites provide approximate pointers, firm calculations call for multiple quotes from well-established contractors, compared line by line for precision.

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.

Wandsworth

Wandsworth is a prominent southwest London borough known for vibrant neighbourhoods like Battersea, Putney, Tooting, Earlsfield, and Wandsworth Town itself. You’ll spot Victorian and Edwardian terraces in areas like Balham or Earlsfield, 1930s semis in Tooting, and modern high-rise apartments near Battersea Power Station. Single-storey rear expansions are often chosen to modernise older ground floors, merging kitchens and dining areas. Side-return extensions are also common in narrower Victorian terraces, harnessing leftover side passages. Loft conversions frequently appear where pitched roofs accommodate extra bedrooms. Basements, while more typical in prime spots near Battersea or close to the Thames, sometimes appear in other pockets if outward expansions aren’t an option.

Local contractors point out that Wandsworth roads, especially near Clapham Junction, Putney High Street, or Tooting Broadway, see considerable traffic, so skip deliveries midmorning can help. Labour fees across Wandsworth are frequently above average, reflecting a strong property market and good transport lines. A well-planned extension can substantially enhance day-to-day comfort and resale appeal, especially near beloved spots like Wandsworth Common, Battersea Park, or Tooting Bec tube. If you share walls in terraced housing, alerting neighbours early and checking for party-wall matters helps smooth the process.

Whether you aim for a single-storey expansion to enlarge a 1930s semidetached in Tooting or a multi-level reconfiguration in a Victorian Battersea terrace, adapting your extension design to Wandsworth’s diverse architecture and local planning policy typically paves a more efficient route to official approval.

Getting Started

Before building, select the extension layout best for your Wandsworth home. A single-storey rear approach can bring together a cramped kitchen and living area into an open-plan hub, while a double storey version offers ground-floor and upstairs expansions—perhaps a new bedroom or a master suite. A side extension utilises an alley or driveway, and for properties lacking outward space, a loft or basement might be viable, although basements generally appear more in high-end roads near Battersea or Putney. Loft conversions remain common in pitched-roof houses throughout Tooting or Earlsfield.

Comprehensive early planning helps avoid confusion once the project is underway. Formulate a detailed budget, reflecting typical local trade costs, materials, and a contingency for structural complexities or high-grade finishing. If your plan demands serious structural modifications—like eliminating key load-bearing walls—an architect or a professional building designer can be invaluable. Some firms provide design-and-build, but they typically require partial sketches or partial consents to quote reliably. Many property owners in Wandsworth first engage an architect, then gather bids from recommended contractors.

It’s prudent to pick your contractor early, since skilled teams around popular zones (Clapham Junction, Balham, Tooting) might be fully booked months in advance. Evaluating multiple quotes lets you parse cost breakdowns meticulously, verify references, and confirm a builder who matches your budget and design vision. A capable builder can refine your blueprint—for instance, placing skylights to enhance daylight or adding a utility nook behind a large kitchen-lounge area.

Project Management

You can organise an extension in one of two primary ways:

1. Single contract (design-and-build or main contractor)
   You sign one contract with a building firm that undertakes or supervises everything—foundation works, structural frames, electrics, plumbing, roofing, finishing. They subcontract trades, usually adding around 10–15% for coordination. This method unifies scheduling and offers one main point of contact.
2. Multi-trade or split contract
   You personally hire groundworkers, carpenters, roofers, electricians, plumbers, etc. Although you spare the main contractor’s markup, you must align each trade’s schedule. If one trade lags, subsequent tasks can’t start, generating possible cost overruns. This arrangement suits owners who have time and some construction knowledge.

For more elaborate expansions in Wandsworth, a single-contractor model is common, especially for owners who prefer minimal daily scheduling. If you choose multi-trade, ensure you can consistently monitor site deliveries and manage the timeline.

Do I Need Planning Permission?

Whether planning permission is needed depends on your extension’s size, height, and boundary relationship. Under Permitted Development Rights, you may enlarge a house without formal planning if your design remains within certain dimension boundaries. If it exceeds them, you file a householder planning permission.

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.

In Wandsworth, certain conservation areas—like parts of Battersea, Wandsworth Town, or Old York Road—may restrict typical PD freedoms. Verify whether your street has particular conditions or Article 4 directions removing PD. Checking with Wandsworth Council or a local planning advisor clarifies whether you’re eligible for PD or if you need an official permission.

Do I Need Planning Permission For A New Storey?

Loft conversions adding dormers or altering roof shapes generally need planning permission. Still, you might add a new storey via permitted development if you meet tight conditions and submit prior approval to the planning office. Otherwise, Householder/Full Planning Permission is standard. If your house meets the requirements, read the bullet points below detailing the constraints:

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.

Additional stipulations may arise upon completion. In older Wandsworth terraces, maintaining roofline consistency can be key to local approval.

Do I Need Planning Permission For A New Basement?

Generally, adding a basement requires planning permission, and large-scale excavation under your home typically also triggers permission because of its scale. Consult Wandsworth Council’s planning department early on if you’re near the river in Battersea or hilly terrain in Tooting or Balham. Basements rank among the costliest expansions, so even if official permission isn’t required in some scenarios, you’ll still need to follow Building Regulations for structural stability, damp-proofing, ventilation, etc.

Local constraints that override PD expansions might exist in prime roads near Wandsworth Common, Battersea Park, or Putney. While basements are less common in typical semidetached areas of Earlsfield or Colliers Wood, some premium roads do see them for maximising living area when outward expansions are limited.

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 a Building notice may be used, but extensive work typically requires a Full Plans Application, in which you provide detailed architectural and structural specifications for approval before construction starts. A Building Notice allows inspectors to approve work in real-time on site.

Keep in mind that some building work can be carried out by qualified trades registered under competent person schemes (e.g. NICEIC for electrics or FENSA for windows). Through these schemes, they can certify compliance themselves, avoiding discrete building control checks for those items.

A Full Plans Application often uncovers any design or safety concerns upfront, while a Building Notice can suffice for simpler expansions. In any situation, building control’s final certificate demonstrates your extension meets code standards.

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

Whereas planning permission checks that the extensions meets local and national planning rules, building control guarantees the structural and regulatory compliance of the works.

Even if your Wandsworth extension is greenlit under PD or obtains planning consent, you still must show building regulations compliance—for instance, confirming foundation adequacy, correct electrics, and suitable insulation. In older Victorian or Edwardian properties across Battersea, Tooting, or Wandsworth Town, verifying that new structural loads remain safe is essential.

DIY Contribution

Homeowners sometimes want to do parts of the extension themselves. Painting, decorating, or landscaping might be feasible DIY tasks if you have the experience. Doing your own demolition, to a degree, may also be viable—if you identify structural walls and follow safety measures carefully.

Nonetheless, installing gas lines, rewiring electrics, or major structural modifications usually demand certified specialists. A mistake can create hazards or lead to big remedial costs. Evaluate your skill level accurately; overcommitting might cause the entire schedule to slip. Builders could pause if your DIY tasks aren’t finished, increasing final expenses. If partial DIY appeals, consult a professional in the initial phase to minimise large missteps.

In Wandsworth, partial DIY typically shows up after the main structural shell is done—like painting or refreshing outdoor areas. Undertaking complex structural or mechanical tasks alone could risk failing official checks or hurting final build quality.

Do I Need An Architect?

If your extension is fairly small and straightforward, you might rely on a structural engineer or building designer. Yet for more substantial or intricate layouts, hiring an architect can yield many benefits. Skilled architects consider day-to-day function, integration of old and new space, plus design harmony.

They can also advise if you remain under PD or must pursue planning consent. While using an architect enlarges initial costs, it can head off expensive mid-project design mistakes.

Wandsworth hosts a spectrum of housing types: Victorian terraces near Battersea, 1930s semis in Tooting, modern apartments around the Thames in Wandsworth Town, etc. An architect might propose partial glass roofs or folding glass walls for a contemporary vibe while preserving a building’s period facade, matching the varied local architecture.

How Long Does It Take To Build An Extension?

Drafting a logical timeline is essential for staying organised. A smaller single-storey build—particularly if it’s standard materials and PD-eligible—might finish within weeks once ground and framing activities commence. Larger expansions, multi-level or multi-room, commonly last several months to half a year or more, dictated by how intricate the structure is and how many trades must coordinate.

Sometimes, a short move-out might be necessary if you remove major supporting walls or if utilities are switched off. Even if you remain on-site, dust, noise, and partial room closures are typical.

Always anticipate potential delays. Adverse weather can pause external tasks, inspectors might request minor layout tweaks, or deliveries might be delayed. Setting a well-grounded schedule with your contractor alleviates pressure, and finishing earlier than expected is welcome. Keep a budget contingency for unexpected structural needs or finishing changes revealed mid-build.

Wandsworth roads near Clapham Junction, Tooting Broadway, or Wandsworth High Street can be heavily travelled, so skip or supply deliveries often fit into midmorning to dodge rush-hour traffic. Revising your structural plan or finishing details after construction commences can also push final completion further out.

House Extensions Step By Step

Though an extension is a major undertaking, with thorough planning, trustworthy professionals, and a regulated budget, it can be accomplished. Whether you want an extended family living area, extra bedrooms, or a basement, track each step and watch for the typical 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. Rectify any finishing defects before releasing the final payment. Keep building control certificates, warranties, and official approvals for future sale or mortgage needs.

When your extension in Wandsworth is finished and passes final inspections, you’ll gain a more spacious and flexible home. Whether you installed a bright kitchen-dining area or added new upper-floor rooms, the outcome often enhances living comfort and property desirability—particularly near sought-after amenities like Wandsworth Common, Battersea Park, or Tooting Bec tube. A snagging survey spots small issues, such as faint cracks or misaligned paint, so they can be remedied prior to handover. Holding onto building control documentation and warranties verifies that your build met all regulations, reassuring future buyers or lenders. With that, your newly expanded Wandsworth residence should serve your evolving household for years to come.