House Extension Quotes
From Local UK Builders
Compare written quotes from local extension builders in your area. Single-storey, double-storey and side extensions — up to 3 free quotes in 24 hours, across 519 towns.
- You choose who to hire — we never charge you
- Single-storey extensions from £22,000 nationally
- Double-storey extensions from £44,000 nationally
- Completely free — no obligation to proceed
What type of extension do you need?
Every type below has its own page with 2026 price ranges, what moves the number, and a quote form matched to that job — so your enquiry reaches builders who do that kind of work. Not sure yet? The cost guide compares them side by side.
How Much Does a House Extension Cost in the UK?
Full cost guide →The most popular choice for UK terraces and semis. Adds a kitchen-diner or extra living space at ground level. Typically 3–5m deep, completed in 10–14 weeks.
Get quotes for this →Maximum space gain in a single build — adds a ground-floor room and a bedroom above. Strong ROI in most UK property markets. Requires full planning permission.
Get quotes for this →Ideal for terraced homes with a narrow side alley. Transforms a cramped kitchen into a full-width open-plan space. Often combined with a rear extension.
Get quotes for this →Costs vary by region, size and specification. Compare 3 quotes from local extension builders for your exact project.
Get free quotes →Regional pricing note: Extension costs vary significantly by region. London and South East prices are typically 25–40% above the national average due to higher labour costs and stricter planning requirements. Use our local cost guide or enter your postcode above for town-specific ranges.
House extension costs at a glance — 2026
Single-storey rear extension — typical 2026 range by region, from this page's cost table.
Source: BestBuilders 2026 quote data · 519 UK towns
House Extensions — What You Need to Know
A house extension is one of the most effective ways to add space and value to your UK home without the cost and upheaval of moving. Whether you need a larger kitchen, an extra bedroom, a home office or a new family living space, an extension lets you reshape your home around how you actually live.
The key to a successful extension is choosing the right builder. BestBuilders passes your job to local extension builders who work with local planning policies, UK building regulations and the structural demands of different property types — from Victorian terraces to post-war semis.
We do not vet the builders who receive your enquiry, so insurance, qualifications and references are yours to check — the section below sets out exactly what to ask for.
How we vet builders →How It Works
Before You Hire, Check They:
Permitted Development & Planning Permission for House Extensions
🏡 Permitted Development
Many single-storey rear extensions qualify under Permitted Development (PD) rights in England — meaning no formal planning application is required, as long as they stay within size, height and materials limits. PD rights do not apply in Scotland, Wales or Northern Ireland in the same way. Your matched builder will advise on PD eligibility for your specific property.
📋 Full Planning Permission
Double-storey extensions, extensions on flats, and properties in conservation areas or with an Article 4 Direction typically require a full planning application. The process takes 8–10 weeks on average. Your builder will advise on what's required for your local authority and can recommend architects who handle extension planning regularly.
🔧 Building Regulations
All extensions — including those under Permitted Development — require Building Regulations approval. This covers structural safety, fire safety, energy efficiency, ventilation and drainage. Building control inspections happen at key stages of the build. Your builder manages this process and provides the completion certificate at the end.
Party Wall Act: If your extension is close to or on the boundary with a neighbouring property, you may need to serve a Party Wall Notice and potentially commission a party wall surveyor. This applies to rear extensions going deeper than 3m (semi-detached) or 6m (detached) under the Neighbour Consultation Scheme. Always check early — the process can add 1–2 months to the pre-construction phase.
House Extension Cost by Region (2026)
Live cost ranges sourced from Best Builders quote data across all 519 UK towns we cover. Figures are mid-range finish; exclude VAT, kitchen and bathroom fit-out, and architectural fees. London prices reflect Zone 1–6 averages.
| Region | Single-Storey Rear | Side Return | Double-Storey |
|---|---|---|---|
| London | £33,000 – £67,000 | £21,500 – £50,500 | £67,000 – £121,000 |
| South East | £30,000 – £60,000 | £19,500 – £45,000 | £60,000 – £108,000 |
| Southern | £27,000 – £55,000 | £17,500 – £41,500 | £55,000 – £99,000 |
| Eastern | £27,000 – £54,000 | £17,500 – £40,500 | £54,000 – £97,000 |
| West Midlands | £25,000 – £50,000 | £16,500 – £37,500 | £50,000 – £90,000 |
| East Midlands | £25,000 – £50,000 | £16,500 – £37,500 | £50,000 – £90,000 |
| Yorkshire | £23,000 – £47,000 | £15,000 – £35,500 | £47,000 – £85,000 |
| North West | £23,000 – £47,000 | £15,000 – £35,500 | £47,000 – £85,000 |
| South West | £23,000 – £46,000 | £15,000 – £34,500 | £46,000 – £83,000 |
| North East | £22,000 – £45,000 | £14,500 – £34,000 | £45,000 – £81,000 |
| Scotland (North) | £23,000 – £46,000 | £15,000 – £34,500 | £46,000 – £82,000 |
| Scotland (South) | £23,000 – £46,000 | £15,000 – £34,500 | £46,000 – £82,000 |
| South Wales | £22,000 – £44,000 | £14,500 – £33,000 | £44,000 – £79,000 |
| Merseyside & N. Wales | £22,000 – £44,000 | £14,500 – £33,000 | £44,000 – £79,000 |
Source: Best Builders 2026 Cost Index, aggregated across 519 UK towns. See full cost index → Ranges reflect mid-spec finishes; premium glazing, structural steel and high-end kitchens move costs above the upper bound. See full cost breakdown →
How to check a builder before you commit
We match you with local trades and step back — the hiring decision is yours. These are the checks that separate a good builder from an expensive mistake, and they take about ten minutes.
Get the quote in writing
An itemised written quote covering labour, materials, waste removal and VAT — not a figure over the phone. If two quotes differ a lot, it is usually because they cover different work, and only the written detail shows you where.
Check the insurance yourself
Ask for the public liability certificate and check the policy is current and in the same trading name as the quote. A logo on a van or a website is not evidence. If the work is notifiable, ask who is registering it.
Ask for recent local work
Two or three jobs of the same type from the last six months, close enough to go and look at. Someone who does good work will offer these before you ask. Be wary of anyone who only has photographs.
On payment: never pay the full amount up front. A deposit against materials is normal; after that, stage payments against completed work are the standard arrangement. Pressure to pay in cash, in full, or on the day is the single most common warning sign.
What’s in an extension price — and what isn’t
Builders quote a build cost, usually per square metre. The professional fees, statutory costs and fit-out sit on top and routinely add 15–25% to the figure people first budget for. Get clear which of these your quote includes before you compare two builders.
| Line item | Typical 2026 cost | In the builder’s quote? |
|---|---|---|
| Build cost, single-storey | £2,000–£3,000 per m² | Yes — this is the headline number |
| Build cost, London & South East | £2,500–£3,800 per m² | Yes |
| Architect or designer | 5–12% of build cost | No — appointed by you |
| Structural engineer | £500–£1,200 | No — needed wherever steels are involved |
| Planning application (householder, England) | around £258 | No — check the current fee, it changes |
| Building control | £500–£1,000 | No |
| Party wall surveyor | £700–£1,500 per neighbour | No — only if the Act applies |
| Kitchen or bathroom fit-out | £5,000–£25,000+ | Usually excluded — check what “finished” means |
| Drainage diversion / deeper foundations | £1,000–£6,000 | No — the classic post-dig variation |
| VAT | 20% | Extensions are standard-rated, unlike new build |
The variation that catches most people is groundworks: a drain, a tree root or poor ground under the footprint is only found once digging starts. Ask each builder what their quote assumes about foundation depth, and what the rate is if it has to go deeper — agreed up front, that is a manageable extra rather than an argument.
How long an extension takes, start to finish
On-site build time is the part people plan for; the approvals in front of it are usually longer. Budget six to twelve months from first conversation to finished room, and start the design and planning work well before you want boots on site.
| Stage | Typical duration | Notes |
|---|---|---|
| Design and drawings | 4–8 weeks | Longer if you iterate on layouts |
| Planning decision (householder) | 8 weeks target | Not needed if it falls under permitted development |
| Building regulations approval | 5–8 weeks | Runs separately from planning — you need both |
| Party wall notices | 2 months’ notice minimum | Start early; this one cannot be compressed |
| Single-storey rear (~20m²) on site | 10–16 weeks | Weather and groundworks drive the range |
| Side return | 12–18 weeks | Access is usually the constraint |
| Double-storey | 16–24 weeks | Roof and structural work add time |
Ask for the programme in writing with milestone dates, and agree what happens if it slips. A builder who will commit to a schedule and stage payments against it is telling you something useful about how they run jobs. See the rear extension cost calculator to size the budget first.
Building regulations and the Party Wall Act
Planning and building regulations are two separate approvals. Plenty of extensions need no planning permission because they fall under permitted development — but essentially every extension still needs building regulations approval. Getting one and assuming it covers the other is the most common and most expensive misunderstanding on this kind of project.
The regs your build will be judged against include Part A (structure and foundations), Part L (insulation and heat loss), Part B (fire, including escape windows and protected routes on two-storey work), Part M (access) and Part P (electrical work). You can go the full-plans route, where drawings are checked before work starts, or a building notice, where inspection happens as you build. Full plans costs a little more time up front and removes most of the risk of being told to undo work.
The Party Wall etc. Act 1996 applies if you build on or at the boundary, cut into a shared wall, or excavate near a neighbour’s foundations. You must serve notice — two months for wall work — and if a neighbour dissents you will need a surveyor. It is not optional and it is not a formality: starting without it can stop the job.
At the end you should receive a completion certificate from building control. Keep it with the planning decision or lawful development certificate; a buyer’s conveyancer will ask for all of it, and reconstructing the paperwork years later is slow and expensive.
Check your specific project
What actually protects you on a build this size
An extension is usually the largest single payment a household makes to a contractor. We do not vet the builders who receive your enquiry, so the protection has to come from how you set the job up — and all of it is arranged before work starts, not after something goes wrong.
A written contract
For anything above roughly £20,000, use a proper contract rather than an emailed quote. A homeowner-scale JCT contract sets out the price, the programme, how variations are priced and what happens if either side wants to stop.
Stage payments and retention
Pay against completed milestones, never in advance of work. Holding back around 5% for six to twelve months after completion gives you real leverage on snagging, which is when most disputes actually happen.
Insurance and warranties
Ask for the public liability certificate and check it is current and in the same name as the contract. For larger builds a 10-year structural warranty is worth pricing — and unlike a builder’s own promise, it survives them going out of business.
Three checks worth making before you sign: the company at Companies House (how long trading, any prior dissolutions), the insurance certificate directly with the insurer, and two recent extensions you can actually go and look at. Any builder worth hiring expects all three.
Extension Builders Across 519 UK Towns
Each town page shows local extension builders, town-specific cost ranges and nearby areas.
House Extension FAQs
Question this page didn't answer?
Ask a specific question about your extension project. A member of our editorial team will answer and publish it (your email is never shown).
Complete your project
Homeowners planning house extension often line up these trades too — get free, no-obligation quotes in the same few clicks.
Our sources for this guide
Cost ranges, timelines and regulatory information on this page are compiled from:
- Federation of Master Builders — Single-Storey Extension Cost Guide
- RICS Building Cost Information Service (BCIS) — Q2 2026 quarterly cost data for UK construction
- Checkatrade — House Extension Cost Guide 2026
- Planning Portal — Extensions, Permitted Development & Planning Permission
- HMRC VAT Notice 708 — Buildings and Construction
- GOV.UK — Party walls and building works
- Best Builders 2026 Quote-Data Index — regional cost ranges aggregated from active quote requests across all 519 UK towns in our network, refreshed quarterly
Editorial standards & how to reach us
Are you an extension builder? List your business on BestBuilders and receive local extension enquiries.
This page is maintained by the Best Builders editorial team. Cost figures are reviewed quarterly against active quote data from active UK extension quotes. Regulatory information (planning, Building Regs, VAT, Party Wall) is checked against current UK government guidance at each refresh. We do not accept payment for editorial coverage; builder listings are earned through our vetting process, not bought.
If you spot an error, have feedback, or want to suggest content improvements, email editorial@bestbuilders.co.uk.
Last updated: 23 May 2026 · Next scheduled review: 23 August 2026