Spanning one of South West London's largest and most varied residential boroughs, Wandsworth covers a wide sweep of the SW18 postcode and sits within the London Borough of Wandsworth — one of the capital's most consistently popular destinations for families and professionals putting down long-term roots. From the Georgian and Victorian streets surrounding Wandsworth Town and the well-kept terraces lining Jew's Row and Alma Road, to the handsome period properties of West Hill and the quieter residential roads stretching towards Earlsfield and Southfields, Wandsworth offers a compelling mix of architectural character, open space, and strong community identity.
For SW18 homeowners, the case for extending rather than upsizing elsewhere is straightforward. Wandsworth's property values have remained resilient across market cycles, and the area's family-oriented demographic means demand for well-configured, generously proportioned homes is consistently high. Whether the goal is a wider ground floor, an additional bedroom, or a proper family kitchen and dining space, a well-designed extension in Wandsworth delivers both the quality of life improvement homeowners are after and a sound long-term return. This guide is written specifically for Wandsworth homeowners and draws on Buildaway's direct experience delivering extensions across the borough, combining realistic 2026 pricing, local planning knowledge, and an 18-month labour warranty on every completed build.
How Much Does a House Extension Cost in Wandsworth (2026)?
Wandsworth sits in the upper-mid range of South West London's construction market. The combination of high-quality Victorian and Edwardian housing stock, strong local demand for experienced builders, and the finish levels expected across SW18 all shape the cost landscape. Below are realistic 2026 mid-market figures:
Single-Storey Rear Extension
- Build-only: £2,700 – £3,600 per m²
- Fully finished with kitchen: £3,600 – £4,800 per m²
- Example: 25 m² kitchen-diner = £67,500 – £90,000 build-only or £90,000 – £120,000 turnkey.
Double-Storey Rear Extension
- Build-only: £2,500 – £3,400 per m²
- Fully finished: £3,400 – £4,600 per m²
- Example: 40 m² across two floors = £100,000 – £136,000 build-only or £136,000 – £184,000 turnkey.
Side Return & Wrap-Around Extensions
Particularly well-suited to Wandsworth's Victorian mid-terrace stock: £2,700 – £3,900 per m², depending on structural complexity, glazing specification, and roof design.
All figures reflect fully compliant, Building Control certified builds meeting Wandsworth Council's current planning and construction standards.
What Drives the Price Up or Down
- Total floor area — the single largest cost determinant across all extension types; a larger footprint increases structural, insulation, and finishing expenditure proportionally.
- Structural steelwork — load-bearing wall removal is a routine requirement in Wandsworth's Victorian terrace and semi-detached stock, typically adding £3,000–£7,000 to the overall project cost.
- Roof design and specification — flat roofs with quality membranes and rooflights are the most cost-effective solution; pitched or lantern roof designs add cost but can meaningfully enhance the quality of natural light in the extended space.
- Glazing and doors — sliding or bi-fold doors opening onto a rear garden are a popular choice in SW18 and add £4,000–£10,000 depending on the size and frame specification selected.
- Conservation area obligations — Wandsworth Town, West Hill, and several other conservation areas within the borough impose material and design requirements that must satisfy the council's planning officers before consent is granted.
- Kitchen and bathroom fit-out — kitchens in the Wandsworth market typically run from £11,000 to £30,000+; bathrooms from £6,500 to £16,000.
- Heating and mechanical upgrades — Megaflo unvented systems or boiler replacements are often required when extensions increase floor area or add bathrooms: £3,000–£5,500.
- Ground conditions — properties in lower-lying parts of SW18 near the River Wandle or the Thames tributary network may sit on less stable ground, occasionally requiring additional foundation investigation prior to design finalisation.
- Site access and logistics — permit parking restrictions, residential road constraints, and skip licensing across Wandsworth's busier streets all contribute to preliminary costs and require careful programme management.
Planning Permission & Building Control in Wandsworth
- Permitted Development (PD): Many single-storey rear extensions in Wandsworth qualify under PD rights, provided they satisfy the council's criteria for depth, height, and materials. Properties within conservation areas or those affected by Article 4 Directions require individual assessment before PD is assumed.
- Neighbour Consultation Scheme: Extensions exceeding standard PD depth limits — up to 6 metres for terraced and semi-detached properties, 8 metres for detached — require formal notification to Wandsworth Council and neighbouring owners. Buildaway handles this process in full on your behalf.
- Full Planning Permission: Required for double-storey extensions, additions visible from the street, front-facing alterations, wrap-around designs, and any proposal falling outside PD thresholds.
- Conservation Areas: Wandsworth Town, West Hill, and other designated conservation areas within the borough require extensions to use materials and designs that are sympathetic to the character of the original building and the surrounding streetscape. Wandsworth's planning officers assess all applications within these zones accordingly.
- Party Wall Act: Wandsworth's dense terrace and semi-detached housing stock means the Party Wall etc. Act 1996 applies to the majority of extension projects in SW18. Written notices must be formally served on all affected adjoining owners before any structural or excavation work begins.
- Building Control: Mandatory for all extension types — covering structural calculations, thermal performance, drainage, fire safety, and electrical compliance. Buildaway coordinates with Wandsworth's building control team and approved private inspectors depending on the requirements of each project.
How Long Will It Take?
- Design and planning preparation: 4–10 weeks
- Technical drawings, approvals, and statutory notices: 3–7 weeks
- On-site construction:
- Single-storey: 10–14 weeks
- Double-storey: 14–20 weeks
- Conservation area applications, bespoke kitchen installations, or specialist glazing may extend the overall programme by two to four weeks beyond these ranges.
Typical Full Project Budget Breakdown (30 m² Double-Storey)
| Element | Typical Cost |
|---|---|
| Core structure & shell | £78,000 – £98,000 |
| Windows / doors / glazing | £5,500 – £11,500 |
| Kitchen supply & fit | £11,000 – £28,000 |
| Bathroom fit-out | £6,500 – £15,000 |
| Heating / boiler / Megaflo | £3,000 – £5,500 |
| Flooring & decorating | £6,500 – £17,000 |
| Professional fees & permissions | £3,500 – £9,500 |
| Total realistic range: | £115,000 – £165,000 |
(Higher-specification finishes, conservation area requirements, or complex foundation conditions can push costs beyond £200,000.)
Why Wandsworth Clients Choose Buildaway
- Borough-wide SW18 experience — practical knowledge of Wandsworth Council's planning policies, conservation area requirements, and the distinctive Victorian and Edwardian housing stock found across the borough.
- Fully transparent pricing — detailed, itemised quotations broken down by trade and project stage, with no vague allowances or charges introduced once work is underway.
- 18-month labour warranty — delivering greater post-completion assurance to Wandsworth homeowners than the standard defects liability period offered by most comparable local contractors.
- Fully accredited and insured — Gas Safe registered, NICEIC certified, and carrying comprehensive public liability insurance on every project without exception.
- Complete project management — Buildaway coordinates architects, structural engineers, Party Wall surveyors, and all specialist trades from the first consultation through to final Building Control sign-off, with clear communication throughout.