How Much Do House Extensions in Lewisham Cost?

House extension costs in the UK range widely, depending on the project’s size, your material choices, and how complex the structural work is. Industry statistics indicate that a single-storey rear extension often begins at around £1,500 per square metre if it’s a simple design, while typical expansions can occupy the £1,800–£2,500 per square metre bracket. Should you introduce high-spec steel structures, customised glazing, or premium decorative finishes, the total can easily surpass £3,000 per square metre.

In Lewisham, located in south-east London, labour fees are typically moderate to high, influenced by the borough’s mix of historic Victorian/Edwardian dwellings and modern developments, as well as proximity to central districts. If you own an older house in areas like Ladywell or Brockley, additional foundational or structural reinforcements might be required, boosting your final bill. Large-scale expansions may land in the £40,000–£100,000+ zone, whereas a smaller side-return extension could be cheaper, and multi-floor or lavish expansions can exceed standard cost levels if advanced engineering or top-of-the-line materials define the build. Incorporating a kitchen or bathroom also inflates costs due to plumbing, electrics, and waterproofing demands.

When you compare quotes, ensure each one details foundation digging, structural framing, roofing, fittings, finishing, labour, overheads, etc. Also clarify if VAT—commonly 20%—is within or outside the stated figure. Though renovation and home-improvement publications can offer general pointers, genuine accuracy in budgeting emerges from collecting quotes from multiple reputable contractors and scrutinising them carefully, item by item.

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.

Lewisham

Lewisham, stretching from New Cross and Deptford to Catford and Downham, is a diverse borough with Victorian terraces, 1930s semis, and modern apartments. Many residents renovate older terraces by expanding the ground floor to achieve open-plan kitchen-dining areas. Others choose side extensions if they have a narrow yard or alley to reclaim. Loft conversions frequently show up in pitched roofs, generating fresh bedrooms or offices. Basements are less common but do appear in certain high-value streets near Blackheath or Brockley, though they often demand detailed engineering checks.

Local contractors emphasise that Lewisham roads near town centres—like Lewisham High Street or Catford—can be congested, so skip deliveries or material drop-offs often work better midmorning. Labour costs are generally a bit below central London rates, yet older properties may require extra measures—like underpinning or better damp-proofing. A well-structured extension can raise daily living comfort and property resale value, especially near strong public transport links (e.g., Lewisham station for DLR and trains). Early communication with neighbours is wise for boundary or party-wall issues—particularly in terraced or closely spaced housing.

Whether your ambition is a single-storey design for a more expansive kitchen-lounge or a multi-level revamp to accommodate a growing family, shaping your plan around Lewisham’s local features and planning procedures is key to a smoother approval process.

Getting Started

Before launching construction, decide which extension method suits your Lewisham property. A single-storey rear addition might link your kitchen and dining room into one big zone, while a double storey arrangement can provide both ground-floor and upstairs expansions. Alternatively, a side extension can recapture a narrow outdoor passage. If outward expansions prove difficult, you might attempt a loft or basement, though basements are typically more complex in this borough.

Solid early planning keeps mid-project chaos at bay. Begin by formulating a comprehensive budget, based on average labour rates, typical material costs, and a buffer for structural or finishing extras. If your design includes major structural changes, an architect or professional designer is beneficial. Some building companies do design-and-build but often need partial sketches or planning consent for a precise quote. Many Lewisham owners hire an architect first, then gather builder quotes.

It also pays to secure a contractor in advance, as good builders often have packed schedules. Comparing quotes early helps you dissect cost differences, check references thoroughly, and choose a team matching your price and style. An experienced contractor might refine your plan—for instance, by inserting a rooflight for added sunlight or creating a utility nook for laundry or storage.

Project Management

In general, you can organise an extension in one of two ways:

• Single contract (design-and-build or main contractor)
  You sign a single contract with a building firm that manages all phases—foundations, framing, electrics, plumbing, roofing, and finishing. They subcontract specialists as needed, charging about a 10–15% markup. This consolidates scheduling and oversight.
• Multi-trade or split contract
  You personally hire each trade—groundworkers, carpenters, roofers, electricians, plumbers, etc. While it might spare you a main contractor’s overhead, you also handle coordination. If one trade lags, the rest might be stuck waiting, escalating stress or costs. This model suits those who can invest time and have some construction familiarity.

For bigger expansions in Lewisham, many owners opt for a main contractor for simplicity. If you prefer multi-trade, prepare to devote time each week to confirm deliveries, check progress, and align tasks without friction.

Do I Need Planning Permission?

Whether you need planning permission depends on your extension’s size, height, and proximity to property edges. Under Permitted Development Rights, you can sometimes enlarge your home without a formal application, provided you respect certain dimension and location constraints. If the proposal stretches beyond these, you generally have to submit 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.

Since Lewisham has areas like Brockley Conservation Area or Blackheath, your property might require stricter external appearance checks. Checking with the borough’s planning office clarifies if PD covers your extension or if a formal application is necessary.

Do I Need Planning Permission For A New Storey?

Loft conversions that change roof shapes or add dormers typically need planning permission. However, you might add a storey using permitted development if you meet certain rules and submit a prior approval to local authorities. Otherwise, Householder/Full Planning Permission is required. If your house meets the criteria, the bullet points below reveal the relevant 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.

Once finished, further stipulations might apply. With Lewisham’s older streets, ensuring any new storey harmonises with surrounding rooflines can be important.

Do I Need Planning Permission For A New Basement?

Creating a new basement typically requires planning permission, and excavating below your dwelling is similarly likely to require permission, given its scale. It’s best to liaise with Lewisham’s planning authority early, clarifying any local constraints. Basements inherently are major endeavours, so even if no formal planning application is demanded, Building Regulations still apply to cover load-bearing issues, ventilation, escape routes, damp control, and more.

Check local guidelines that might override standard PD expansions. Some roads in Lewisham—particularly in Blackheath or Brockley’s conservation areas—impose stricter requirements. Consulting council resources or a planning specialist helps confirm if your basement is feasible.

Although basements are not as ubiquitous in Lewisham as in more central boroughs, some homeowners in more expensive roads or near the borough’s greener pockets do consider them for extra living room if 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 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 identifies potential design or safety flaws upfront, whereas a Building Notice can work for smaller expansions. Both routes conclude with building control approval, certifying compliance with code standards.

Building work involving electrical, heating, plumbing, or window installations can be certified by registered professionals through Competent Person Schemes (such as NICEIC for electrical work or FENSA for windows), allowing them to self-certify compliance without requiring separate building control inspections.

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 Lewisham extension is allowed under PD, you still need building regulations approval to ensure safe structural changes, suitable insulation, and so on. Given many older properties in areas like Catford or Deptford, verifying foundational strength is typically critical.

DIY Contribution

Homeowners sometimes consider tackling parts of an extension themselves. Painting, decorating, or landscaping can be good DIY tasks if you possess the skill and time. Doing your own demolition, to some extent, might also be possible—if you identify which walls are load-bearing and follow standard safety measures.

However, tasks like installing gas lines, rewiring electrics, or adapting key structural supports almost always require licensed professionals. Errors here can be expensive and risky. Being candid about your capabilities is essential; overcommitting could cause delays. Builders may hold off if your DIY tasks aren’t done, elevating total costs. If you do want to handle some aspects yourself, professional input upfront helps you avoid severe missteps.

In Lewisham, partial DIY is common at the finishing stage—like painting walls or minor landscaping. Taking on advanced structural or engineering roles yourself might delay official inspections or compromise final quality.

Do I Need An Architect?

If your extension is straightforward, a structural engineer or a building designer might suffice. Yet for a bigger or more sophisticated plan, an architect frequently supplies notable advantages. Good architects weave functionality, lighting, and design unity so that your new extension melds smoothly with existing spaces.

They can also confirm if planning permission is required or if PD covers the build. While an architect raises early costs, it typically prevents mid-project design changes or mistakes that can inflate the budget later.

Lewisham features a variety of housing: from Victorian terraces around Brockley to 1930s semis near Catford, plus modern flats near Lewisham town centre. An architect might suggest solutions that mesh older exteriors with fresh interior expansions, potentially including bigger windows or partial glass ceilings to bring in natural light.

How Long Does It Take To Build An Extension?

Laying out a viable schedule helps manage the build. A smaller single-storey rear design—especially if simple, common materials, and PD-eligible—could finalise in several weeks once on-site work starts. Larger expansions, multi-room or multi-level, can stretch from a few months to half a year or more, reflecting structural complexity and the trades needed.

Sometimes, you may relocate temporarily if main walls are demolished or if essential services must be disconnected. Even if you remain, plan on dust, noise, and certain rooms being off-limits.

Always include some slack time. Poor weather might hinder exterior tasks, building inspectors might request small revisions, or deliveries can run late. Coordinating a practical timeline with your contractor reduces stress, and finishing early is a pleasant result. Similarly, a budget contingency handles unforeseen structural tasks or design shifts mid-project.

Lewisham sees congestion near main roads such as the A2 or Lewisham High Street, so booking skip or supply deliveries outside rush hours helps. Changing layout or finishes once the build is underway can also push your final completion date further.

House Extensions Step By Step

Though building an extension is a considerable effort, with methodical planning, reliable trades, and a properly allocated budget, success is within reach. Whether you want to enlarge a kitchen-lounge area, add more bedrooms upstairs, or incorporate a basement, it pays to watch each phase and 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. Correct any remaining faults prior to final payment. Keep building control sign-offs, warranties, and relevant documentation for a future property sale or mortgage.

Once your Lewisham extension concludes and receives sign-off, you can revel in a larger, more functional living environment. Whether you formed a light-filled rear family zone or built an entirely new storey, the outcome often boosts comfort and possible resale value, particularly if you’re near transport nodes like Lewisham station or the borough’s numerous green spaces. A snagging survey ensures minor cracks, paint discrepancies, or other finishing flaws are resolved before your contractor departs. Storing building control certificates and warranties validates your adherence to regulations, soothing any doubts from lenders or prospective buyers. Then, your newly expanded Lewisham house can serve your family’s evolving needs for the foreseeable future.