House Extensions
Professional house extensions built to your exact specification. From single-storey rear extensions to full double-storey builds — we handle the lot.
Extend Your Home, Not Your Mortgage
If your home is starting to feel cramped but you love your neighbourhood, a house extension is almost always better value than moving. You avoid estate agent fees, stamp duty, solicitor costs, and the sheer headache of uprooting your life. A well-built extension gives you the space you need while adding genuine value to your property.
We build house extensions across the UK — from compact side-returns in London terraces to large wrap-around extensions on detached homes in Manchester and Birmingham. Every project is different, and we approach each one on its own merits. No cookie-cutter solutions.
Whether you need a bigger kitchen, an extra bedroom, or a dedicated home office, the right extension transforms how you live. We work with you from initial sketches through to snagging, managing the build so you don't have to chase subcontractors or worry about building regs compliance.
Why Extend?
The average cost of moving home in England is around £12,000–£15,000 once you factor in stamp duty, solicitor fees, estate agent commissions, surveys, and removal costs. For many homeowners, that money is better spent on an extension that gives you exactly the space you want — without packing a single box.
Extensions also let you design your space from scratch. You choose the layout, the ceiling height, the window positions, the flow between rooms. You're not compromising with someone else's floor plan.
From a property value perspective, a well-executed extension in a desirable area can add 10–20% to your home's value. In parts of London and the South East, that can mean a six-figure increase on a relatively modest build spend. Even in areas where the maths is tighter, you're still creating a better home for your family while building equity.
Types of House Extension
The right type of extension depends on your property, your plot, what you need the space for, and your budget. Here are the main options we build regularly.
Single-Storey Rear Extension
The most popular type of extension in the UK. Built off the back of your house, typically extending 3–8 metres into the garden. Perfect for creating an open-plan kitchen-diner or a larger living space. Most rear extensions under 6m (semi-detached) or 8m (detached) fall under permitted development, so you won't need planning permission. Expect a build time of 10–14 weeks and costs from £1,500–£2,500 per m².
Double-Storey Extension
Adds space on two levels — typically a kitchen or living area downstairs with a bedroom and bathroom above. Costs roughly 50–60% more than a single-storey but gives you double the floor area, making it excellent value per square metre. Always needs planning permission as it extends beyond permitted development limits. Build time is typically 14–20 weeks. Foundations need to be deeper to carry the extra load.
Side Return Extension
Common on Victorian and Edwardian terraced houses where there's a narrow alleyway running alongside the kitchen. By building over this dead space — often just 1–1.5 metres wide — you can significantly widen your ground floor. Combined with a rear extension, this creates a large open-plan space. Side returns typically fall under permitted development if they don't exceed half the width of the original house.
Wrap-Around Extension
Combines a rear extension with a side extension to create an L-shaped addition. Maximises your ground floor space and is particularly effective on corner plots or properties with wide side access. Wrap-arounds almost always require planning permission due to their footprint. Build time is 12–18 weeks. Costs start around £45,000 for a modest wrap-around but can reach £80,000+ for larger builds with high-spec finishes.
Side Extension
Built on the side of your property, often to add a garage, utility room, or widen the house footprint. Works well on detached and semi-detached homes with sufficient side access. Under permitted development, a side extension can't exceed half the width of the original house and must be single-storey with a maximum height of 4 metres. Often combined with internal remodelling to integrate the new space properly.
Over-Structure Extension
Building above an existing single-storey structure — like a garage or flat-roofed kitchen — to add a first-floor room. This approach avoids new foundations entirely, which saves significant cost. However, the existing structure needs to be assessed by a structural engineer to confirm it can take the load. If the existing foundations and walls are adequate, this is one of the most cost-effective ways to add a bedroom or office.
House Extension Costs in 2026
Every extension is priced individually, but these figures give you a realistic idea of what to budget. All prices include VAT and are based on a mid-range specification with quality materials.
Single-Storey Rear (20m²)
£35,000 – £55,000
Includes foundations, blockwork, roof, windows/doors, insulation, electrics, plastering, and basic decoration. Does not include kitchen fitting or bespoke joinery. A flat roof with lantern light adds roughly £3,000–£5,000 over a standard pitched roof.
Double-Storey Rear (40m²)
£55,000 – £90,000
Same as single-storey plus first-floor joists, staircase modifications, additional bedroom/bathroom shell. Deeper foundations (typically 1.5m+ due to extra load) and steel beams throughout. Scaffolding is a larger cost — budget £2,000–£4,000.
Side Return (8–12m²)
£20,000 – £40,000
Smaller footprint but often involves structural steelwork to remove the existing side wall and open up the kitchen. Glazed roof sections are popular and add £150–£250 per m². A smaller project but can transform a narrow galley kitchen into a proper room.
Wrap-Around (30–40m²)
£45,000 – £80,000
Combines rear and side into one build. More complex foundations where the two wings meet, and often requires significant steelwork. Planning and design fees are higher, but you get maximum ground-floor space. Bi-fold doors across the rear are standard — budget £3,000–£6,000 for a 4m set.
Regional Price Differences
Location has a significant impact on extension costs. Labour rates, material delivery costs, and local demand all vary. As a rough guide:
London & South East: £2,200–£3,000/m²
Highest labour costs in the UK. Skip permits, parking restrictions, and limited access often add 10–15% to costs in inner London boroughs.
Midlands & North West: £1,500–£2,200/m²
Birmingham, Manchester, Liverpool — competitive labour market keeps prices reasonable. Good availability of trades.
North East & Yorkshire: £1,400–£2,000/m²
Leeds, Sheffield, Newcastle — generally the lowest build costs in England, though material costs are similar nationwide.
South West & Wales: £1,600–£2,300/m²
Bristol and Bath sit at the higher end. Rural areas can be more expensive due to delivery logistics and limited trade availability.
Planning Permission & Building Regulations
Permitted Development Rights
Under the Town and Country Planning (General Permitted Development) Order, many extensions don't need planning permission. The key limits for houses (not flats or maisonettes) are:
Single-storey rear extensions: Up to 6m from the rear wall (semi-detached/terraced) or 8m (detached). Maximum eaves height of 3m. If within 2m of a boundary, maximum eaves height of 3m.
Side extensions: Single-storey only, maximum height 4m, width no more than half the original house. Must be set back at least 1m from the front elevation on the side facing the highway.
Double-storey rear: No more than 3m from the rear wall. Must be at least 7m from the rear boundary. Roof pitch must match the existing house. Cannot include a balcony or raised platform.
These rights can be removed or restricted by Article 4 directions, conservation area designations, or conditions on your original planning permission. Always check with your local authority.
Building Regulations
Even if you don't need planning permission, you always need building regulations approval for a house extension. This covers:
Part A — Structure: Foundations, walls, steelwork, and roof must be structurally sound. Your structural engineer's calculations get submitted here.
Part B — Fire Safety: Fire escape routes, smoke alarms, fire-resistant materials between the extension and any attached garage or boundary.
Part L — Conservation of Energy: Insulation values (U-values) for walls, roof, and floor. Windows must be double-glazed and meet minimum standards. As of 2025, the requirements are tighter — walls need a U-value of 0.18 W/m²K or better.
Part P — Electrical Safety: Any new electrical circuits or work in bathrooms/kitchens must be signed off by a Part P registered electrician or inspected by building control.
Part M — Access: If you're extending at ground level, the extension should have level or ramped access. Door openings must be at least 775mm clear width.
We handle the building regs application and manage all inspections throughout the build.
How Long Does a House Extension Take?
Every project is different, but here's what a typical timeline looks like from first contact to moving in the furniture.
Design & Planning
4–8 weeks. Initial consultation, site survey, architectural drawings, structural calculations. If planning permission is needed, add 8 weeks for the standard application process (13 weeks for larger or complex schemes).
Pre-Build
2–4 weeks. Building regs application submitted, party wall notices served (if applicable — allow 2 months for party wall agreements), materials ordered, site prep. We schedule trades and confirm the start date.
Build Phase
10–20 weeks depending on scale. Foundations and groundwork (1–2 weeks), walls and roof (3–5 weeks), first fix electrics and plumbing (1–2 weeks), plastering and second fix (2–3 weeks), decoration and snagging (1–2 weeks).
What to Expect When Building an Extension
Before the Build
We start with a site visit to understand your property, discuss what you want to achieve, and flag anything that might affect the design or cost — drainage runs, tree roots, boundary issues, overhead cables.
Your architect (we can recommend one or work with yours) produces drawings. Our structural engineer calculates the steelwork, foundations, and any load-bearing modifications. We submit the building regs application and, if needed, the planning application.
If you share a wall with a neighbour, the Party Wall Act 1996 requires you to serve notice at least two months before starting work. We'll guide you through this — most neighbours agree quickly, but some appoint their own surveyor (at your cost, typically £700–£1,500 per neighbour).
Once approvals are in place, we provide a fixed-price quote with a full breakdown and a detailed programme of works.
During the Build
Foundations: Trenches dug, inspected by building control, then filled with concrete. Strip foundations are standard (typically 600mm wide, 1m+ deep), though in areas with clay soil or near trees, you may need deeper trench-fill or even piled foundations.
Walls & Roof: Blockwork goes up, DPC (damp-proof course) is laid, lintels and steels installed. The roof structure goes on — either pitched tiles to match your existing roof or a flat warm-deck roof with membrane.
Weathertight: Once windows and doors are fitted and the roof is on, the shell is weathertight. This is when internal work begins — first fix plumbing and electrics run through the walls and floor before plastering.
Finishing: Plastering, second fix (sockets, switches, radiators, bathroom fittings), decoration, flooring. The final step is the knock-through — removing the existing external wall to open up into the new space. This is the exciting bit.
Building control inspect at key stages: foundations, DPC, drainage, structural steel, and a final inspection before issuing your completion certificate.
Other Services You Might Need
Many of our extension clients also look at these complementary projects — often it makes sense to combine work to save on setup costs and disruption.
Kitchen Extensions
If your extension is primarily about the kitchen, see our dedicated kitchen extension page for specific guidance on layouts, utility connections, and integrating appliances into a new build.
Loft Conversions
Combining an extension with a loft conversion maximises your space on both levels. We can manage both projects simultaneously, reducing overall build time and costs.
Bathroom Renovations
Adding a bathroom to your extension? Whether it's a downstairs WC or a first-floor ensuite in a double-storey build, see our bathroom renovation page for specification guidance.
Garage Conversions
If you have an integral or attached garage, converting it can be a cost-effective alternative or addition to a traditional extension — typically 30–40% cheaper per square metre.
House Extension Questions
Common questions from homeowners planning an extension. If yours isn't answered here, get in touch — we're happy to help.
Common Questions
Details regarding our process, planning constraints, and project timelines.
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