House Extension London - Vetted Builders, 3 Free Quotes

Q: What are the different types of house extensions in London?

There are six main types: rear extension (often permitted development, £60,000–£160,000); side return extension (infills the side passage, £50,000–£90,000); wrap-around extension (rear + side return combined, £130,000–£380,000); double-storey extension (planning permission required, £120,000–£320,000); over-garage extension (often permitted development, £40,000–£80,000); and basement extension (specialist contractors required, £150,000–£400,000+).

Q: How much does a house extension cost in London?

House extension costs in London range from £2,800–£5,500 per m² depending on specification and borough. A single-storey rear extension typically costs £60,000–£160,000, a double-storey extension £120,000–£320,000, and a wrap-around extension £130,000–£380,000. Basement extensions are the most expensive at £150,000–£400,000+.

Q: Do I need planning permission for a house extension in London?

Many house extensions in London qualify as permitted development and do not require planning permission — subject to size limits, height restrictions, and boundary rules. Single-storey rear extensions up to 4m deep (detached) or 3m deep (semi/terraced) typically qualify. Extensions in conservation areas, listed buildings, or those exceeding permitted development limits require full planning permission. Building regulations approval is required for all extensions.

Q: How long does a house extension take in London?

A single-storey rear extension takes 3–5 months from start to completion, including 6–10 weeks on site. A double-storey or more complex extension takes 5–9 months in total. Add 8–16 weeks for design, planning permission, and tendering before work starts.

Q: Do I need a party wall agreement for a house extension in London?

A party wall agreement is required if your extension involves work on or near a shared wall, boundary, or foundation within 3–6 metres of a neighbouring property. This applies to most rear and side return extensions on London terraced and semi-detached houses. A party wall surveyor must be appointed and notices served before work begins — typically costing £700–£2,000 per affected neighbour.

Q: Does a house extension add value in London?

A well-designed house extension typically adds 10–20% to a London property's value. On a £700,000 property that equates to £70,000–£140,000 in added value. Adding a bedroom and bathroom via a double-storey extension consistently delivers the strongest return.

Q: Do I need an architect for a house extension in London?

An architect or architectural designer is strongly recommended for most house extensions — for planning drawings, building regulations submissions, and contractor oversight. Architect fees typically run 8–15% of the build cost for a full service.

Submit your extension brief in 3 minutes. We match you with vetted house extension builders specialists in London's planning rules, party wall requirements, and structural constraints and send you competing quotes with full cost breakdowns.

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🏗️ Extension From £2,500/m²

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What happens next

We review your brief and match it with vetted builders who specialise in your project type.

Matched builders review your brief and may contact you to clarify details before quoting.

You receive up to 3 competing quotes with full cost breakdowns. Choose with no obligation.

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WHAT WE COVER

What types of house extension can you get quotes for in London?

London’s housing stock terraced Victorians, Edwardian semis, post-war semis, modern townhouses each comes with its own constraints and opportunities. We match you with extension builders who know your property type and your borough.

🔙 Rear Extension

The most common house extension in London. Single-storey rear extensions up to 3–4m deep often qualify as permitted development. Typically £60,000–£120,000 for a standard single-storey build.

↔️ Side Return Extension

Infilling the narrow side passage common on London Victorian terraces. Creates a wider kitchen-diner without losing garden space. Typically £50,000–£90,000 depending on length and specification.

⬆️ Double-storey extension

Adding two floors to the rear or side: a bedroom above and a kitchen-diner below. Requires planning permission in most cases. Typically £120,000–£320,000, delivering strong ROI.

🔄 Wrap-Around Extension

Combining rear and side return into a single L-shaped extension. Maximises ground-floor living space dramatically. Typically £130,000–£380,000 depending on size and specification.

🏠 Over-Garage Extension

Building above an integral or attached garage to add a bedroom or office. Often qualifies as permitted development. Typically £40,000–£80,000, one of the most cost-effective ways to add space.

⬇️ Basement Extension

Excavating below ground level to create additional living space is increasingly popular in prime London boroughs. Requires specialist contractors and significant structural work. Typically £150,000–£400,000+.

HOW IT WORKS

How do you get house extension quotes in London?

Three steps. No account required. No calls from builders we haven’t specifically matched to your extension type and borough.

Tell us about your Extension

Extension type, property, whether you have planning permission or need it, rough budget, and your London postcode. We ask the right questions so builders can price accurately.
3 MINUTES

We Match and Notify

We review your brief and send it to vetted extension builders covering your area. They may contact you to discuss scope, structural requirements, or planning before preparing a quote.
24–48 HOURS

Receive and Compare Quotes

Up to 3 itemised quotes within 5 working days. Compare scope, build specification, structural allowances, and timeline. Choose with no obligation.
WITHIN 5 WORKING DAYS

WHY IT MATTERS

Why does a house extension in London need a specialist builder?

House extensions are among the most complex residential projects in London. Structural, planning, legal, and technical requirements all converge on a single build. A builder without London extension experience can cost you far more than the saving on their quote.

🏗️ Structural and RSJ Experience

Almost every rear or side return extension requires steelwork RSJ beams to carry loads where walls are removed. Extension specialists work with structural engineers and know how to specify, supply, and install steelwork correctly to comply with building regulations.

📋 London Planning Knowledge

Permitted development rules, conservation area restrictions, Article 4 directions, and borough-specific policies vary considerably across London's 33 boroughs. Extension builders on our network have live experience navigating planning in your specific area.

🤝 Party Wall Expertise

Most London terraced and semi-detached extensions trigger party wall obligations. Extension specialists understand the notice process, surveyor requirements, and how to manage neighbour relationships minimising delays before work begins.

📐 Verifiable Extension References

Every builder on our network must provide references from comparable London extension projects not general building work. We verify these before any builder receives a lead from us.

SETTING EXPECTATIONS

What should a house extension quote in London include?

Extension quotes vary more than almost any other renovation type because the structural and planning variables differ on every project. A single headline figure tells you very little. A properly itemised quote should break down every major cost centre so you can compare like-for-like.

If a quote you receive doesn’t explicitly cover these items, ask the builder to clarify before proceeding. QuoteMyRenovation builders are briefed to provide detailed breakdowns; let us know if one falls short. House Extension London

Structural engineer's report and RSJ beam specification

Planning application fee and drawings (if required)

Building regulations drawings and submission

Party wall surveyor costs (per affected neighbour)

Groundworks, foundations, and drainage

Structural steelwork supply and installation

External walls, roof structure, and weatherproofing

Windows and external doors supply and fitting

Insulation to current building regulations

First and second fix electrics

Plastering, internal finishing, and decoration

Payment schedule tied to build milestones

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COMMON QUESTIONS

Frequently asked questions about house extension London

Questions homeowners ask us most often before submitting their house extension brief.

What are the different types of house extensions in London?

There are six main types of house extensions available to London homeowners. A rear extension adds space to the back of the property; single-storey rear extensions up to 3m deep (terraced or semi-detached) often qualify as permitted development (£60,000–£160,000). A side return extension infills the narrow side passage on Victorian and Edwardian terraces, widening the ground floor without losing garden (£50,000–£90,000). A wrap-around extension combines rear and side return into an L-shape for maximum ground floor space (£130,000–£380,000). A double-storey extension adds two floors, increasing bedroom count and delivering the strongest property value uplift; planning permission is nearly always required (£120,000–£320,000). An over-garage extension builds above an existing integral garage, often without planning permission; one of the most cost-effective options (£40,000–£80,000). A basement extension excavates below ground level and requires specialist contractors, planning permission, and structural and waterproofing expertise (£150,000–£400,000+).

How much does a house extension cost in London?

Do I need planning permission for a house extension in London?

How long does a house extension take in London?

Do I need a party wall agreement for a house extension in London?

Does a house extension add value in London?

Do I need an architect for a house extension in London?

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Submit your brief in 3 minutes and receive up to 3 itemised quotes from vetted house extension builders covering your London borough.

London, United Kingdom

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