How Much Do House Extensions in South London Cost?

Throughout London, extension costs can vary enormously depending on how large your design is, the materials you pick, and the structural complexity. Industry sources often cite that a single-storey rear extension may begin near £1,500 per square metre for a simple plan, whereas mainstream expansions commonly range in the £1,800–£2,500 per square metre zone. If you plan advanced steel frameworks, intricate glazing, or high-end internal finishes, total costs can exceed £3,000 per square metre.

In South London, an area spanning multiple boroughs like Lambeth, Southwark, Wandsworth, and Croydon, labour rates typically hover from moderate to high, influenced by proximity to central hubs and strong property markets. If your home is a Victorian terrace in Brixton, a semidetached in Streatham, or an Edwardian house in Balham, structural reinforcements, damp-proofing, or deeper foundations may be required, lifting your final outlay. Larger expansions often land in the £40,000–£100,000+ bracket, while smaller side-return or single-floor additions might cost less. Ambitious multi-level or opulent designs surpass conventional cost thresholds if engineering challenges or premium materials define the project. Adding a bathroom or kitchen further inflates the budget because of pipework, electrical lines, and waterproofing.

When reviewing builder quotes, confirm each itemises foundation tasks, structural frames, roofing, fixtures, finishing, labour, overhead, etc. Also check if VAT—typically 20%—is within or outside the sum. Although renovation media and websites can yield approximate guidelines, real precision comes from collecting multiple estimates from reputable construction teams and comparing them meticulously, 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.

South London

South London comprises a wide area south of the River Thames, typically including boroughs like Lambeth, Southwark, Wandsworth, Croydon, and beyond. Properties vary enormously: Victorian terraces in Clapham or Tooting, 1930s semis in Bromley or Sutton, new flats in Nine Elms, or period houses in Dulwich. Single-storey expansions often unify small kitchens and lounges into expansive, modern zones. Side-return extensions can harness narrow spaces along older terraces, typical in boroughs like Lambeth. Loft conversions are also common throughout, carving pitched roofs into additional bedrooms or offices. Basements pop up in premium roads near places like Battersea or Dulwich, though engineering complexities and higher budgets apply.

Local contractors highlight that South London roads near Clapham Junction, Brixton, or Croydon town centre can be congested, so scheduling skip or material deliveries outside busy commuting times is practical. Labour fees track moderate to high, given strong property prices and varied architectural heritage. A well-planned extension can raise day-to-day comfort and home appeal, especially near vibrant local hubs or transport lines—like the Northern line in Balham or Overground stops in Peckham. Letting neighbours know about your intentions can help, notably if you share boundary walls in closely spaced terraces.

Whether you want a single-storey rear extension to open up a ground floor or a multi-floor strategy creating additional upstairs bedrooms, adapting your scheme to the character and regulations of South London—and to your specific borough’s planning policies—generally makes for smoother approvals and a cohesive final design.

Getting Started

Before building, decide which extension arrangement befits your property in South London. A single-storey rear design might expand your cooking and dining area, while a double storey build grants further living capacity at both ground and upper floors. Alternatively, a side extension can reclaim a driveway or alley, typical in 1930s semis. If outward expansion is tricky, a loft or basement might be relevant—though basements in South London vary by area, being more frequent in pricey neighbourhoods like Dulwich or Battersea, whereas loft conversions flourish in many pitched-roof houses across Lambeth or Croydon.

A robust plan from the start averts mid-project holdups. Develop a clear budget referencing standard building labour fees, average material expenses, and a contingency to handle structural unknowns or upscale finishing. If your blueprint involves major structural changes—like removing large load-bearing walls—then employing an architect or professional building designer can help. Some contractors do design-and-build, but typically need partial drawings or planning consents for accurate quotes. Many South London households initially hire an architect, then collect quotes from chosen builders.

It’s crucial to organise your contractor well ahead, as proficient trades fill their schedules quickly—particularly near times of local events or peak renovation seasons. Evaluating quotes thoroughly allows you to parse cost details, interview references, and settle on a builder aligned with your budget. A knowledgeable builder may also refine your concept—for example, adding roof lanterns for extra daylight or converting leftover corners into a utility nook.

Project Management

Extensions typically are managed in one of two ways:

1. Single contract (design-and-build or main contractor)
   You sign a single deal with a main contractor that executes all tasks—foundation work, structural building, electrics, plumbing, roofing, finishing. They subcontract trades, normally applying a 10–15% fee for coordination. This arrangement merges scheduling, giving you a central contact for everything.
2. Multi-trade or split contract
   You personally hire each trade: groundworkers, carpenters, roofers, electricians, plumbers, plasterers, etc. Although you might avoid a main contractor’s overhead, you must coordinate timetables meticulously. If a trade is late finishing, subsequent tasks must wait, raising frustration or cost. This approach suits homeowners with enough free time and some building knowledge.

For larger expansions in South London, the single-contractor model is common, especially for owners who want minimal day-to-day oversight. If you prefer multi-trade, ensure you can regularly check the site, align deliveries, and keep tasks in sequence to avoid major disruptions.

Do I Need Planning Permission?

Whether you need planning permission depends on your extension’s scale, height, and location on the property. Under Permitted Development Rights, you can occasionally extend your house without a formal planning submission, provided your layout stays within certain limits. If it surpasses these, you typically lodge a householder planning permission application.

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.

South London includes many conservation pockets—like in Dulwich Village, certain parts of Wandsworth Town, or Streatham. Some expansions that might otherwise fall under PD may therefore need extra design checks or planning consent. Checking your borough’s planning rules or seeking a planning consultant early usually clarifies if PD covers your plan or if a formal application is needed.

Do I Need Planning Permission For A New Storey?

Loft conversions altering roof shapes or adding dormers often require planning permission. Yet you could add a new storey via permitted development if you meet specific standards and submit a prior approval to your borough planning office. Otherwise, Householder/Full Planning Permission is standard. If your house meets these criteria, the bullet points below define 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.

Further rules could apply post-build. In many South London terraces, consistent rooflines or local design guidelines might shape how feasible extra storeys are.

Do I Need Planning Permission For A New Basement?

Constructing a new basement typically demands planning permission, and excavating below your property likewise often requires it because of the project’s scale. Engaging your borough’s planning authority early clarifies any local constraints—particularly in areas prone to high water tables or near the Thames (like parts of Lambeth or Wandsworth). Basements count among the most involved extensions, so even if official planning consent might not be triggered in some cases, Building Regulations definitely apply for structural safety, damp control, escape routes, etc.

Confirm local rules beyond PD expansions. Some roads in Dulwich or Wandsworth’s older enclaves might limit or discourage subterranean work. Consulting your council or a planning consultant is typically wise.

Basements are more frequently found in affluent roads near Battersea or Clapham, but can appear in pockets of Bromley or Croydon if outward expansions are restricted. Expect higher engineering fees and potential party-wall negotiations if you attempt one in South London.

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 have to submit a building regulations application. For smaller scale projects you can issue a Building notice, but bigger extensions usually demand a Full Plans Application, wherein detailed specifications are approved prior to building. A Building Notice has an inspector approve the works as they develop.

It’s worth noting that installations for electrics, heating, plumbing, or windows may be undertaken by qualified specialists registered under competent person schemes (e.g. NICEIC for electrical or FENSA for windows). With these schemes, such professionals can self-certify their work, bypassing separate building control checks for those particular installations.

A Full Plans Application lets you catch design or safety issues before the project starts, whereas a Building Notice might suffice for simpler expansions. Either path, you’ll need final building control sign-off to confirm the completed extension adheres to codes.

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 emphasises structural safety, regulatory adherence, and practical compliance.

Even if your South London extension is allowed under PD or you successfully gain planning consent, you must still secure building regulations compliance—for example, robust foundations, correct ventilation, fire checks, and so forth. In older Victorian or Edwardian terraces across Lambeth, Croydon, or Wandsworth, ensuring your structural modifications remain safe is a priority.

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DIY Contribution

Homeowners sometimes intend to perform parts of an extension themselves. Painting, decorating, or landscaping can be suitable DIY tasks if you possess the proper skillset and time. Doing your own demolition, to a certain extent, may also be feasible—if you verify which walls provide structural support and follow safety measures strictly.

However, tasks involving electrics, gas lines, or critical structural changes nearly always require licensed professionals. Errors there can be hazardous or lead to massive costs for rework. Judging your competence accurately is vital; overshooting can delay progress. Builders might wait if your DIY tasks run behind schedule, raising the overall budget. If you want partial DIY, seeking professional advice initially helps avoid major slip-ups.

In South London, partial DIY typically emerges after structural phases end—like painting or reorganising the garden. Handling advanced mechanical or engineering tasks alone might cause you to fail official checks or reduce build quality.

Do I Need An Architect?

If your planned extension is relatively straightforward, you might suffice with a structural engineer or design professional. But for bigger, more intricate designs, an architect offers substantial benefits. A skilled architect weaves functionality, daylight, and aesthetic unity, ensuring the new space pairs well with the existing home layout.

They can also determine if your design fits PD or calls for planning permission. Though an architect’s fee increases initial costs, it frequently saves money by preventing design errors or structural oversights further along.

South London covers an array of districts: period terraces in Brixton, spacious semis in Beckenham (though partly in Bromley), modern developments near Nine Elms. An architect might suggest partial glass ceilings or folding walls to create an open living environment, bridging older exteriors with fresh, contemporary additions.

How Long Does It Take To Build An Extension?

Crafting a realistic timeline is crucial. A smaller single-storey rear extension—if it’s straightforward, typical materials, and permitted development—could wrap up in a matter of weeks once the ground and structural phases begin. Larger expansions, multi-floor or multi-room, regularly last from several months to half a year or more, reflecting engineering complexities and how many different trades must coordinate.

Sometimes, you might relocate temporarily if crucial walls are removed or if essential utilities are disrupted. Even if you remain, anticipate dust, drilling noise, and partially restricted rooms for the project’s duration.

Always build in spare time for complications. Severe weather might delay external works, building inspectors might insist on small design tweaks, or deliveries can arrive behind schedule. Setting a sensible timeline with your contractor minimises stress, and completing earlier than projected is always a bonus. Similarly, a financial buffer is worthwhile for unforeseen structural tasks or finishing changes discovered mid-flow.

South London sees high traffic near big transport hubs—like Brixton, Clapham Junction, or Croydon town centre—so scheduling skip drop-offs outside the rush helps. Adjusting your structural layout or interior finishes once building starts can extend the finishing date further.

House Extensions Step By Step

Though taking on an extension is extensive, with a grounded plan, a dependable team, and an organised budget, you can accomplish it. Whether you want a more spacious kitchen-diner, upstairs bedrooms, or even a basement, ensure each phase is addressed and watch out for known 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. Any outstanding details should be rectified prior to final payment. Store building control certificates, warranties, and official approvals in a safe place for mortgage or property sale.

Upon the completion and sign-off of your extension in South London, you’ll have a larger, more practical home environment. Whether you introduced a sunny rear lounge, constructed a second level, or formed a new loft room, the outcome generally benefits your everyday comfort and potential resale value—especially near sought-after spots like Clapham, Dulwich, or Balham. A snagging survey verifies finishing errors (e.g., hairline cracks, paint blemishes) so your builder can handle them. Holding onto building control records and warranties confirms your project adhered to regulations, reassuring prospective buyers or lenders. With that final detail sorted, your newly expanded South London home can serve you and your family’s evolving needs for years ahead.