How much does a single storey extension cost in London in 2026?

In London in 2026 a single storey extension typically costs between 30,000 and 120,000 pounds including VAT, depending on size and route. A compact 3m x 3m extension runs roughly 30,000 to 48,000 pounds, a full-width 3-metre rear extension 48,000 to 65,000 pounds, a side return extension 60,000 to 85,000 pounds, a 4 to 5 metre rear kitchen-diner 65,000 to 95,000 pounds, and a wrap-around 95,000 to 120,000 pounds. As a guide that is about 2,800 to 5,500 pounds per square metre including structural steel and building control. Industry guides quote lower national per-metre figures, but London and the South East run 30 to 50 percent above the national average, and many quotes exclude VAT and professional fees. We fix the price in writing after a free survey, and every figure includes VAT.

How much does a 3 metre house extension cost?

A 3 metre house extension in London typically costs 48,000 to 65,000 pounds including VAT for a full-width rear extension on a terrace or semi, or roughly 30,000 to 48,000 pounds for a compact 3m x 3m scheme. The 3-metre depth is popular for a reason: on most houses it can be built as permitted development with no planning application, and it is usually enough to turn a cramped kitchen into a proper kitchen-diner. We confirm what 3 metres would achieve on your house at a free survey.

Do you need planning permission for a single storey extension?

Often not. A single storey rear extension of up to 3 metres on a terraced or semi-detached house, or 4 metres on a detached house, is usually permitted development, and up to 6 or 8 metres is possible with prior approval where neighbours are consulted first. A side extension can be permitted development if it is no wider than half the original house, and a wrap-around always needs a full application. The extension must be no more than 4 metres high with eaves no higher than 3 metres within 2 metres of a boundary. We confirm your exact route at the free survey, and where the work is permitted development we recommend a Lawful Development Certificate so you hold council paperwork proving it.

How long does a single storey extension take to build?

Most single storey extensions take around 10 to 16 weeks on site depending on size, glazing and groundworks, with a wrap-around at the longer end. Before work starts there is a design and approvals stage covering drawings, any planning application or prior-approval notification, and party wall notices, so allow a few months from first survey to breaking ground. We give you a realistic programme with the fixed-price contract.

Should a single storey extension have a flat roof or a pitched roof?

Both work well and the right answer depends on your house, your budget and the light you want. A flat roof costs less, suits roof lanterns and gives clean modern lines; a pitched roof matches period properties, gains internal ceiling height, sheds rain better and often pleases planners in conservation areas. Under permitted development the extension must stay within 4 metres total height either way. We design both and show you the difference for your house at the free survey.

Does a single storey extension need deep foundations?

Every single storey extension needs proper foundations, typically at least a metre deep, but the exact depth depends on your soil, nearby trees and drains. In much of West London the clay soil and street trees mean building control often asks for deeper foundations than homeowners expect, and this is one of the most common sources of surprise costs on poorly quoted jobs. We assess the ground at the survey, price the foundations realistically in the fixed price, and building control inspects the excavation before concrete is poured.

Can you build a single storey extension on a bungalow?

Yes, bungalows suit single storey extensions particularly well. The same permitted development rules apply, and because the whole house is on one level the new space connects naturally to the existing rooms. A rear or wrap-around extension can transform a bungalow's living space, and it pairs well with a loft conversion if you also want an extra bedroom upstairs. We design around your plot and planning position at the free survey.

Are modular or prefab single storey extensions any good?

Modular and kit extensions are genuinely fast and can suit simple garden rooms, but they have trade-offs for a permanent house extension: the components are standardised rather than designed around your house, matching the existing brickwork is harder, which matters for permitted development and planning, and resale surveys tend to favour traditional construction. A traditionally built brick extension takes longer but matches the house, satisfies the matching-materials rule, and is built around your exact layout. We build traditionally, with oak-frame and timber-frame options where the design suits them.

Rear, side return or wrap-around, which single storey extension should I choose?

It depends on what your ground floor lacks. If the kitchen is wide enough but too small, a rear extension adds depth and is often permitted development. If you have a narrow galley kitchen beside a dead side alley, a side return extension adds the width that transforms it. If you want the full open-plan kitchen-dining-living transformation, a wrap-around combines both. Each has its own dedicated page on our site, and we recommend the right route for your house honestly at a free survey.

West London & Surrey Extension Specialists

Single-Storey
Extension London

A single-storey extension is the most popular home improvement in London for a simple reason: one new ground-floor space, whether a 3 metre house extension at the rear or a full wrap-around, transforms how the whole house lives. Many need no planning application at all. We design and build single-storey extensions across West London and Surrey under one fixed-price contract, with planning, party wall, structural steel, glazing and building control handled in-house, and every price including VAT.

📋 Book Free Survey 📞 +44 7404 931629

2010Building Since

10–16Weeks On Site

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Inc VATFixed-Price

📐

PD & Planning Handled

We find your fastest lawful route and handle the paperwork

💷

Fixed Price Inc VAT

The survey number is what you pay, with no surprise 20%

🧱

Party Wall Handled

We manage the whole neighbour & party wall process for you

✅

Building Regs Sign-Off

Full compliance and completion certificate included

What Is A Single-Storey Extension?

One storey, maximum transformation

A single storey extension adds ground-floor space without building upwards: one new room, or one much bigger room, at garden level. It is the workhorse of London home improvement because the structure is simpler than building up, the build is faster, and many schemes qualify as permitted development with no planning application at all.

It comes in four shapes, and we build them all: a rear extension for depth, a side return extension for width, a wrap-around for both, and the kitchen extension that most of them become. Brick to match the house as standard, with oak-frame and timber-frame options where the design suits.

Whatever the shape, the deal is the same: design, planning, party wall, structure, glazing and building control handled in-house, one fixed price including VAT, and a 2-year workmanship guarantee. See our extension cost guide and planning guide for the deeper detail.

★★★★★

Three metres off the back of the house and it feels like a different home. No planning needed, the party wall sorted with both neighbours, and the price never moved…

Verified client · West London

Google & Checkatrade reviewed

Finished single-storey extension in London: a bright open-plan kitchen-diner at garden level with rooflights and doors opening onto the garden — Completed Single-Storey ExtensionA 3-metre rear extension turned into a garden-facing kitchen-diner, West London

The Sweet Spot

The 3-Metre Extension

Ask any London builder which extension gets built most and the answer is the same: the 3 metre house extension. It is the sweet spot where planning freedom, cost and transformation meet.

3m The depth most houses
can build without a
planning application

1No planning application on most houses. A single-storey rear extension of up to 3 metres on a terrace or semi (4 metres detached) is usually permitted development. That saves the £548 fee and roughly 8 weeks of waiting, and we recommend a Lawful Development Certificate so you hold council proof.
2Three metres changes the room. Across the full width of the house it is enough to turn a cramped kitchen into a proper kitchen-diner with a table or island. Even a compact 3m x 3m extension adds a genuine extra room.
3The best cost-to-change ratio. Simple structure, straightforward roof, no upper floors to support: a 3-metre extension delivers more transformation per pound than any other extension we build. Want to go deeper? Up to 6m (8m detached) is possible with prior approval, covered on our rear extension page.

The rules in one line: maximum height 4 metres, eaves no higher than 3 metres within 2 metres of a boundary, matching materials, measured from the original rear wall, and no more than half the garden covered. This is a general guide (current as of July 2026, per the Planning Portal), not formal planning advice for your property: the free survey confirms your lawful route in writing before anything is built.

Roof Options

Flat Roof Or Pitched Roof?

The roof shapes how a single-storey extension looks, feels and costs, and it is the decision most quotes never discuss. Here is the honest comparison; we design both and show you the difference for your house at the free survey.

Factor	Flat Roof Extension	Pitched Roof Extension
Look	Clean, modern lines; parapet or slim fascia detail	Traditional; matches period tiles and rooflines
Light	Perfect for roof lanterns and large flat rooflights	Velux-style rooflights in the slope; vaulted ceilings possible
Ceiling	Consistent height throughout	Extra height at the ridge; a vaulted ceiling feels dramatic
Cost	The more cost-effective option	More structure and tiling, so typically costs more
Planning & PD	Easily stays within the 4m PD height limit	Often preferred by planners on period streets and in conservation areas
Maintenance	Modern membranes last decades; needs occasional checks	Tiles shed rain and leaves naturally; very long-lived

Most of our clients choose a flat roof with a lantern for modern kitchen-diners and a pitched roof where the extension needs to sit quietly against a period house. Both are designed to your house, not from a catalogue.

Four Ways To Build It

Single-Storey Extension Ideas

Every single-storey extension takes one of four shapes, and each has its own dedicated page with costs, planning rules and design detail. The new space can be a kitchen-diner, dining room, family room, home office or utility: we draw the floor plan around how you live.

Single-Storey Rear Extension

The most popular shape: 3 to 6 metres of depth into the garden, often with no planning application. Full detail, depth bands and costs on our rear extension page.

Single-Storey Side Extension

Fills the side return of a terrace or the side passage of a semi, adding the width a narrow kitchen lacks. Full detail on our side return extension page.

Terrace classic£60k–£85k

Best for: Victorian and Edwardian galley kitchens.

Single-Storey Wrap-Around

Side and rear combined into one L-shape for the biggest ground-floor transformation a house can take. Always needs planning, always worth designing properly: see our wrap-around extension page.

Maximum space£95k–£120k

Best for: families wanting kitchen, dining and living in one.

Bungalow Extension

A single storey bungalow extension keeps the whole home on one level while adding the space the original floor plan never had. The same PD rules apply, and it pairs beautifully with a bungalow loft conversion for an extra bedroom.

One-level livingOften PD

Best for: bungalows across the Surrey belt.

Match Your Home

The Right Single-Storey Extension For Your House

Use this as a starting point. Every house, boundary and budget is different, so we confirm the best design and the planning route on the free survey.

Your Home	Best Option	Why
Terrace or semi, kitchen too small	3-metre rear extension	Usually permitted development; the best cost-to-change ratio there is.
Victorian terrace, narrow galley kitchen	Side return extension	The dead side alley becomes the width the kitchen always lacked.
Semi-detached with side access	Side or wrap-around	The side passage gives more width to play with; ideas for semi-detached houses start there.
Want the full open-plan space	Wrap-around extension	Width and depth together; the biggest single-storey transformation.
Bungalow	Rear or wrap bungalow extension	One-level living with the space the plot always allowed.
Period house, conservation street	Pitched-roof rear (with planning)	A sympathetic roof and matching brick keep planners comfortable; we design for approval.
Tight budget, one extra room	Compact 3m x 3m extension	A genuine new room at the lowest sensible cost, often under permitted development.

Transparent Pricing

Single-Storey Extension Cost, London 2026

Single-storey extension costs depend on size, shape, roof and glazing. The ranges below are for London in 2026 and include the structural shell, roof, standard glazing, plastering and building control. Every price includes VAT. National guides quote lower per-metre figures, but London and the South East run 30 to 50 percent above the national average, and most quotes you will see exclude VAT and professional fees. For the full picture see our house extension cost guide.

Project	Typical London Cost	Build Time	Planning
Compact 3m x 3m extension	£30,000 – £48,000	8–10 weeks	Usually PD
Full-width 3-metre rear extension	£48,000 – £65,000	10–12 weeks	Usually PD
Side return extension	£60,000 – £85,000	12–14 weeks	Often needed
Rear kitchen-diner (4–5m)	£65,000 – £95,000	12–16 weeks	PD / prior approval
Wrap-around extension	£95,000 – £120,000	16–20 weeks	Full planning
Roof lantern & bifold upgrade	+ £6,000 – £15,000	Within build	Included in build

Indicative London ranges for 2026, including VAT, structural steel and building control, at roughly £2,800–£5,500 per m². For context, the FMB's national guide quotes £1,800–£3,000 per m² excluding London's 30–50% uplift, VAT and professional fees. Try our free single storey extension cost calculator for a tailored estimate.

Where you can keep the cost down. Staying within the 3-metre permitted development band avoids fees and months of waiting. After that, a flat roof with a standard rooflight instead of a lantern, standard doors instead of full-width bifolds, and keeping drainage near its existing runs each save thousands. Foundations are the one place never to economise: West London clay and street trees often demand deeper digs than expected, which is why our fixed price is set after a proper survey, not a doorstep guess.

Planning & Permitted Development

Do You Need Planning Permission?

Often, no. Single-storey extensions enjoy the most generous permitted development rights in the planning system, and the route depends on the shape you choose. We confirm your exact position at the survey and prepare whichever application or certificate your project needs. Full guidance is on the Planning Portal, and we cover it in our extension planning guide.

✅ Often No Application Needed

✓ Rear: up to 3m (4m detached) as standard PD; up to 6m/8m with prior approval, neighbours consulted first
✓ Side: single storey, no wider than half the original house, max 4m high
✓ Height limits: 4m maximum, eaves ≤3m within 2m of a boundary; matching materials; no more than half the garden covered
✓ Where the work is PD, we recommend a Lawful Development Certificate (£274) so you hold council paperwork proving it

📋 Planning Permission Needed

→ Every wrap-around extension (the L-shape is outside PD)
→ Side extensions in conservation areas, and the 6m/8m route on designated land
→ Schemes beyond the PD limits, flats, maisonettes and listed buildings
→ Householder fee £548, decision typically in around 8 weeks, prepared and managed by us

The party wall bit everyone worries about. On a terrace or semi the build or the excavation almost always involves the boundary, so the Party Wall etc. Act 1996 applies and notices must be served. It is routine, and we manage the whole process for you. These notes are a general guide (current as of July 2026), not formal planning advice for your property: the free survey confirms your lawful route in writing before anything is built.

What's Included

One Fixed Price, Everything Handled

A single-storey extension touches groundworks, drainage, structure, roofing, glazing and fit-out, so a clear scope matters. Here is what our fixed price includes as standard, and what to budget separately.

✓ Included As Standard

✓ Free survey, feasibility & measured drawings
✓ Structural engineer's calculations & steel beams
✓ Planning application, prior-approval notification or LDC
✓ Party wall notices & process management
✓ Foundations, groundworks & drainage diversions
✓ Structural opening into the existing house (where wanted)
✓ Roof, flat or pitched, with rooflights, weathertight
✓ Insulation to Part L, plastering & first-fix M&E
✓ Building control sign-off & completion certificate
✓ Scaffolding, skip hire & site management

+ Budget Separately For

+ Kitchen units & appliances if it becomes a kitchen (see our kitchen extension page)
+ Bifold or sliding doors (upgrade from standard glazing)
+ Roof lantern (upgrade from standard rooflights)
+ Oak-frame or timber-frame upgrade where the design suits
+ Flooring: tile, engineered wood or polished concrete
+ Underfloor heating (popular at garden level)
+ Decoration, lighting design & landscaping
+ £548 planning fee or £274 LDC (third-party council cost)

All build prices include VAT. The council application fee is a third-party cost outside the build, but we list it up front so nothing is a surprise.

How It Works

Our Five-Step Process

From first survey to the finished room, a clear process keeps a single-storey extension on time and on budget, with no surprises in scope, timing or cost.

Free Survey & Feasibility

Our project manager measures the rear and side, checks the ground, drains, trees and the original rear wall, and talks through the shape, the planning route and a realistic budget. Around 45 minutes, no obligation.

Design, Plans & Approvals

Drawings, single-storey extension plans and engineering are prepared in-house. We submit the planning application, prior-approval notification or LDC and serve party wall notices, all managed for you.

Fixed-Price Contract

You get a written contract, inclusive of VAT, covering every element. The agreed price does not change unless you request a change.

Build & Fit-Out

Foundations dug to suit your ground and inspected by building control before concrete, then drainage, steel, walls, roof and glazing, then insulation, plastering and first-fix. Inspections at every key stage.

Completion & Sign-Off

Building control issues the completion certificate. The same project manager who did your first survey walks you through the finished room, fixes any snags and hands over your written workmanship guarantee.

Adds Space, Light & Value

The Most Popular Home Improvement In London

There is a reason the single-storey extension is the project London homeowners choose most: it adds the space families actually use, at garden level where life happens, without the cost and complexity of building upwards. The open-plan, garden-facing ground floor it creates is the feature estate agents consistently rate as the most sought-after in a family home, and because so many schemes qualify as permitted development, it is often the improvement with the least planning risk and the most predictable timeline.

"One storey is all it takes. Get the shape, the roof and the light right and a single-storey extension changes every single day you live in the house."

Hiring Pitfalls

Red Flags When Hiring

Most extension disputes come from the same warning signs at quoting stage. Watch for these before you sign, ours included.

Foundations Priced On A Guess

West London clay and street trees often demand deeper foundations than expected. A doorstep quote that hasn't assessed the ground is a variation invoice waiting to happen. Ours is priced after a proper survey.

A "From" Price That Excludes VAT

Many extension quotes look cheap because the "from" figure leaves off 20% VAT, the steel or the fees. Ask for the all-in number. Ours is fixed and includes VAT.

Measures From The Wrong Wall

PD depth is measured from the original rear wall, not the current one. A builder who doesn't ask whether the house has been extended before may promise "no planning needed" and deliver an enforcement case.

No Structural Engineer

Opening the back of the house needs proper steel and calculations. A quote with no engineer's input is guessing at the most critical part of the job.

Vague On Planning & Party Wall

The shape decides the planning route, and a terrace or semi almost always triggers the Party Wall Act. A builder who waves both away is storing up delays and disputes.

No Address Or Recent Projects

Check Companies House and ask for recent local jobs. We are on Google and Checkatrade with a real Hayes address you can verify.

Where We Build

Single-Storey Extensions Across West London & Surrey

From our Hayes base we cover West London, South-West London and Surrey: street after street of terraces, semis and bungalows built for exactly this improvement, with councils whose approach to extensions we know well.

UB · Hillingdon

Hayes, Uxbridge & Ruislip

Our home patch: semis and terraces where a 3-metre rear extension creates the kitchen-diner the original floor plan never allowed. See our Hayes page.

W3 · W5 · W13

Ealing, Acton & Hanwell

Victorian terrace country where single-storey side returns and rear extensions transform narrow ground floors, with conservation pockets handled carefully.

TW · Hounslow

Hounslow, Isleworth & Chiswick

Period terraces and 1930s semis where a ground-level extension opens the house to the garden, with planning routes we know well.

TW1 · TW9

Twickenham & Richmond

Sought-after period stock, often in conservation areas where a pitched roof and matching brick win approval. See our Richmond page.

KT · Kingston

Kingston, Surbiton & New Malden

Semis with the width and gardens for deeper single-storey schemes, islands and full-width glazing onto the garden.

Surrey

Esher, Cobham, Weybridge & Egham

Across the Surrey commuter belt, detached homes and bungalows where generous plots take the largest single-storey extensions, planning handled for you.

Got Questions?

Single-Storey Extension FAQs

A single storey extension adds ground-floor space to your house without building upwards: one new room, or one much bigger room, at garden level. It can extend to the rear, fill the side return of a terrace, or wrap around the back corner, and it is most often used to create an open-plan kitchen-diner. Because it is one storey, the structure is simpler, the build is faster, and many schemes need no planning application at all.

Typically £30,000–£120,000 including VAT depending on size and shape: a compact 3m x 3m around £30,000–£48,000, a full-width 3-metre rear £48,000–£65,000, a side return £60,000–£85,000, a 4–5m kitchen-diner £65,000–£95,000 and a wrap-around £95,000–£120,000. That is roughly £2,800–£5,500 per m² including steel and building control; national guides quote less, but London runs 30–50% above the national average and most quotes exclude VAT. See the cost guide or try the free calculator.

In London, a full-width 3 metre house extension typically costs £48,000–£65,000 including VAT, and a compact 3m x 3m scheme roughly £30,000–£48,000. The 3-metre depth is the sweet spot: on most houses it needs no planning application, and it is usually enough to turn a cramped kitchen into a proper kitchen-diner. We confirm what 3 metres would achieve on your house at a free survey.

Often not. A rear extension up to 3m (4m detached) is usually permitted development, with 6m/8m possible via prior approval. A side extension can be PD if it is no wider than half the original house. A wrap-around always needs a full application, as do schemes in conservation areas, flats and listed buildings. Height is capped at 4m with eaves at 3m near boundaries. We confirm your route at the survey, and where the work is PD we recommend a Lawful Development Certificate (£274). More in our planning guide.

Most take around 10 to 16 weeks on site depending on size, glazing and groundworks, with a compact 3m x 3m nearer 8–10 weeks and a wrap-around up to 20. Before work starts there is a design and approvals stage covering drawings, any application and party wall notices, so allow a few months from first survey to breaking ground. We give you a realistic programme with the fixed-price contract.

Both work well. A flat roof costs less, suits roof lanterns and gives clean modern lines; a pitched roof matches period properties, gains ceiling height at the ridge, and often pleases planners in conservation areas. Under permitted development the extension must stay within 4 metres total height either way. We design both and show you the difference for your house at the free survey.

Every extension needs proper foundations, and the depth depends on your soil, nearby trees and drains. In much of West London, clay soil and street trees mean building control often requires deeper foundations than homeowners expect, which is a common source of surprise costs on poorly quoted jobs. We assess the ground at the survey, price the foundations realistically in the fixed price, and building control inspects the excavation before any concrete is poured.

Yes, bungalows suit them particularly well. The same permitted development rules apply, the new space connects naturally because the whole home is on one level, and a rear or wrap-around extension transforms the living space. It also pairs well with a loft conversion if you want an extra bedroom upstairs. We design around your plot at the free survey.

They are fast and can suit simple garden rooms, but for a permanent house extension they have trade-offs: standardised components rather than a design around your house, harder brick matching, which matters for the permitted development matching-materials rule, and resale surveys tend to favour traditional construction. We build traditionally in brick to match, with oak-frame and timber-frame options where the design suits, so the extension looks like it was always part of the house.

It depends on what your ground floor lacks. Kitchen wide enough but too small: a rear extension adds depth, often without planning. Narrow galley kitchen beside a dead alley: a side return adds the width that transforms it. Want the full open-plan space: a wrap-around combines both. Each has its own page with costs and rules, and we recommend honestly at the free survey.

One Storey, Whole New House

Book Your Free
Extension Survey

Our project manager will visit, measure the rear and side, check the ground and the planning position, and tell you exactly what a single-storey extension would cost on your house, fixed in writing and including VAT, with planning and party wall handled for you. Or get an instant estimate with our free calculator.