How Much Does a House Extension Builder Cost in London? (2026 Price Guide)
⏱ 8 min read
- Typical price range
- £5,800 – £145,000
- Average hourly rate
- £60 – £100 per hour
- Typical job duration
- 8–20 weeks
- Certification required
- Building Regulations approval; FMB member recommended
House Extension Builder Cost in London
If you need to hire a house extension builder in London, knowing what to expect to pay before making any booking is essential. London is located in Greater London, and house extension builder prices here typically sit well above the UK national average. This 2026 price guide covers typical job costs, hourly rates, the factors that drive price variation, and practical advice on finding a qualified, trustworthy house extension builder in London.
London's housing stock is predominantly Victorian and Edwardian across inner boroughs, with a high proportion of period flats and conversions that require specialist knowledge of older pipe materials, lath-and-plaster ceilings, and original sash windows. Clay soil across much of Greater London causes seasonal ground movement, making subsidence a recurring concern for older foundations — groundwork and drainage costs are typically higher here than in most UK cities. The London Building Act applies additional requirements for certain structural and drainage works beyond standard Building Regulations, and many inner London boroughs have extensive conservation area designations that affect permitted development rights.
House Extension Builder prices within London itself can vary between postcodes: properties in premium or central areas may attract a further 10–15% premium compared to less central parts of the city. Demand peaks between November and February, when prices can rise 10–20% and availability tightens — booking ahead is strongly advisable.
Average House Extension Builder Cost in London (2026)
House extension builder costs in London vary considerably depending on the type of work, its complexity, and whether standard or emergency rates apply. The prices below represent typical ranges for common house extension builder jobs in London in 2026:
Single-storey rear extension: £29,000 – £72,500
Double-storey extension: £58,000 – £130,500
Side return extension: £36,250 – £79,750
Wraparound extension: £65,250 – £145,000
Kitchen extension: £36,250 – £87,000
Orangery/glass extension: £43,500 – £108,750
Basement conversion: £43,500 – £116,000
Porch extension: £5,800 – £21,750
Garage to extension conversion: £21,750 – £58,000
Utility room extension: £21,750 – £50,750
Most homeowners in London pay around £36,250–£79,750 for a typical house extension builder job, though the final figure depends on the exact scope, materials, and access at your property.
Prices include labour. Materials may or may not be included — always confirm with your tradesperson. Emergency and out-of-hours work typically attracts a 30–60% surcharge on top of standard rates.
What Is Included in the Price?
A standard house extension builder quote should typically cover:
- Labour for groundworks, foundations, brickwork, roofing, and the full structural shell of the extension
- Building Regulations applications, staged inspections, and a completion certificate on sign-off
- Standard foundations, drainage connections, and a damp-proof course tied into the existing structure
- First-fix and second-fix electrics and plumbing where included, plus plastering and insulation to current standards
- Standard internal finishes, doors, and windows ready for decoration as set out in the agreed specification
Items generally not included unless explicitly stated:
- VAT (20%) — confirm whether your quote is inclusive or exclusive of VAT (new-build extensions are standard-rated)
- Architect's drawings, structural engineer's calculations, and planning application fees (arranged separately)
- Planning permission where the extension exceeds permitted development limits, and any associated planning conditions
- Party wall awards and surveyor fees where the work affects or sits near a neighbour's boundary or wall
- Kitchen units, bathroom suites, flooring, final decoration, and landscaping unless specifically itemised
Typical House Extension Builder Hourly Rates in London (2026)
Hourly rates for house extension builders in London depend on time of call-out, the tradesperson’s experience, and the nature of the work. The table below shows representative ranges for 2026:
| Time of Call-Out | Typical Hourly Rate (London) |
|---|---|
| Standard hours (Mon–Fri, 8am–6pm) | £60 – £100 |
| Evening (Mon–Fri, 6pm–10pm) | £80 – £130 |
| Weekend (standard hours) | £85 – £140 |
| Bank holidays & overnight | £115 – £190 |
Most house extension builders in London charge a minimum call-out fee equivalent to 30–60 minutes of work, regardless of actual job length. Always confirm whether call-out charges and VAT are included in any quoted figure before booking.
Factors That Affect House Extension Builder Costs in London
Several variables can significantly influence what you end up paying for house extension builder work in London:
- Type and complexity of work: Simple maintenance tasks cost a fraction of major installations or structural projects. Always request an itemised written quote.
- Urgency: Emergency same-day or out-of-hours call-outs in London attract surcharges of 30–60% on top of the standard rate. Booking ahead saves money.
- Materials and parts: Replacement parts are almost always charged on top of labour unless the quote explicitly states otherwise. Ask for a separate breakdown.
- Access and location: Difficult-to-reach areas — lofts, crawlspaces, confined spaces — increase labour time and total cost considerably.
- Regulatory requirements: Work requiring Building Regulations approval; FMB member recommended certification commands higher rates, reflecting the training, ongoing registration, and insurance obligations involved.
- Seasonality: Demand for house extension builders typically peaks in certain months (especially winter for heating and drainage work, and summer for exterior and garden work). Booking 4–6 weeks in advance secures better rates.
- Reputation and experience: Highly rated professionals with extensive verifiable reviews tend to charge more — but this often means fewer call-backs and better long-term outcomes.
- Location within London: Tradespeople further from the city centre may charge less in travel time and costs, yielding savings of 5–15% with minimal quality impact.
DIY vs Hiring a Professional House Extension Builder
Important: Certain house extension builder work is legally required to be carried out by a professional holding Building Regulations approval; FMB member recommended certification. Undertaking regulated work without the correct qualifications can invalidate your home insurance, breach building regulations, and — in serious cases — create significant safety risks. Never attempt to bypass these legal requirements to save money.
An extension is a major structural build that must be designed to a structural engineer's calculations and constructed in compliance with the Building Regulations, with Building Control inspecting key stages from foundations upward and issuing a completion certificate at the end. Self-managing trades is possible for an experienced project manager, but the structural design, foundations, steelwork, and damp-proofing must be done correctly — defects here are hidden, expensive to remedy, and will be flagged on a future survey. Confirm at the outset whether the extension is permitted development or needs full planning permission, and whether a party wall award is required before any work begins.
You should always hire a professional house extension builder for work that:
- Requires legal certification or involves compliance with building regulations.
- Affects the structural integrity or the safety systems of your property.
- Needs to be backed by a formal written guarantee or manufacturer’s warranty.
- Could cause significant or costly damage if performed incorrectly.
For small, cosmetic or inherently low-risk tasks — such as minor adjustments, surface painting, or straightforward component replacements — a competent DIYer may proceed safely. When in doubt, the cost of a professional is almost always justified against the potential expense of rework or repairs.
House Extension Builder Cost Comparison: London vs Other UK Cities (2026)
The table below compares typical house extension builder hourly rates across a selection of major UK cities in 2026, to help put London’s pricing in context:
| City | Average House Extension Builder Hourly Rate |
|---|---|
| Manchester | £40 – £65 |
| Birmingham | £35 – £65 |
| Leeds | £35 – £65 |
| Bristol | £45 – £80 |
| Edinburgh | £40 – £75 |
| Oxford | £50 – £85 |
| Cambridge | £50 – £85 |
| Glasgow | £40 – £65 |
| London (this guide) | £60 – £100 per hour |
London consistently commands the highest house extension builder rates in the UK. Cities in the North, Midlands, Scotland, Wales, and Northern Ireland tend to be lower. Hiring a house extension builder based just outside London’s central area may save 10–15% with no significant difference in quality or response time.
Tips to Save Money on House Extension Builder Work in London
- Obtain at least three fixed-price quotes against one detailed specification and drawing set — vague or unusually cheap quotes almost always become more expensive through variations once work is under way.
- Hold back a retention (commonly around 5%) until snagging is complete and the Building Regulations completion certificate is in hand, and tie staged payments to inspected milestones rather than calendar dates.
- Reuse the existing roofline and keep services (kitchen, bathroom) on the same side as existing pipework where the design allows — shorter drainage and supply runs cut groundwork and plumbing costs.
- Obtain at least three written quotes before committing. Use Checkatrade, Rated People, or MyBuilder to contact multiple vetted professionals in London quickly.
- Book during standard working hours — scheduling non-urgent work on weekday mornings avoids evening, weekend, and emergency surcharges.
- Ask about supply-and-fit options — sourcing your own materials or fixtures can save 15–30% on the parts element, though always confirm in advance that the tradesperson is comfortable with this arrangement.
- Request a fixed-price quote for complex or time-uncertain jobs to remove the risk of costs escalating if the work takes longer than expected.
- Schedule preventive maintenance — annual servicing and early-stage repairs invariably cost less than emergency call-outs or full replacements.
- Check for local authority or government schemes — certain energy efficiency, insulation, or statutory improvement works may qualify for grants or council-funded support. Check gov.uk for current programmes.
- Plan ahead and avoid peak demand — booking 4–6 weeks in advance, particularly before the winter rush, secures better availability and stronger negotiating position on price.
Questions to Ask Before Hiring a House Extension Builder in London
Before signing any agreement or paying a deposit, ask every prospective house extension builder these key questions:
- Are you fully qualified and certified to Building Regulations approval; FMB member recommended standard, and can you provide documentary proof?
- Do you carry public liability insurance, and to what level of cover?
- Can you provide a detailed written quote that itemises all work, materials, and costs before you begin?
- Is VAT included in your quoted price, and will you issue a formal VAT receipt or invoice?
- Do you charge a separate call-out or minimum visit fee, and how is this applied?
- What is your realistic timeframe for starting and completing the work, and how will you communicate any delays?
- Do you offer a workmanship guarantee, and for how long?
- Can you provide details of two recent customers I can contact as references?
Red Flags: Warning Signs of a Cowboy House Extension Builder
- Requesting a large upfront cash payment before any work has been started — a deposit of 10–20% is reasonable; anything more is concerning.
- Unable to produce proof of qualifications, insurance, or certification on request — any legitimate professional will have these documents readily available.
- Refuses to provide a written, itemised quote and insists on verbal-only pricing with no breakdown of costs.
- Significantly undercutting all other quotes — an unusually low price often indicates corner-cutting on materials, inadequate insurance, or undisclosed add-on charges.
- Pressuring you to make an immediate decision — a trustworthy tradesperson will always give you time to compare alternatives and think carefully.
- No verifiable online presence or reviews — check Google, Checkatrade, and Companies House registration. Refusal to supply references is a serious red flag.
How to Find a Trusted House Extension Builder in London
- Verify registration or accreditation using the official Federation of Master Builders online checker — this takes seconds and is the most important first step for any regulated trade.
- Use vetted platforms such as Checkatrade, Rated People, or TrustMark to find reviewed house extension builders in London.
- Ask for personal recommendations from neighbours, friends, or colleagues — word of mouth from people you trust remains the most reliable method.
- Check recent Google Business reviews for consistent positive comments on punctuality, tidiness, communication, and value for money — not just an overall rating.
- Confirm public liability insurance of at least £1 million before any work begins. Any reputable professional holds this as standard and will produce evidence promptly.
- Never pay the full amount upfront — a deposit of 10–20% is standard practice; the balance should only be paid once the work is completed to your satisfaction.
Frequently Asked Questions
How much does a house extension cost in the UK?
House extension costs in London range from £1,200–£2,500 per m² of new floor area for a standard specification. A typical single-storey rear extension of 20 m² costs £25,000–£50,000; a two-storey extension costs £45,000–£90,000. Final cost depends on finish specification, demolition work required, structural complexity, and regional rates — London and the South East typically cost 20–35% more. Always get at least three written quotes from London builders before committing.
Do I need planning permission for a house extension?
Many single-storey rear extensions fall under Permitted Development (PD) rights and do not require planning permission if they meet specific limits (e.g. no more than 3m beyond the rear of a terraced house, or 4m for a detached). A Householder Application is required for extensions that exceed PD limits, two-storey side extensions, or any extension in a Conservation Area or listed building. Always contact your London local planning authority or a planning consultant to confirm before starting.
How long does a house extension take to build?
A single-storey rear extension of 15–30 m² typically takes 10–20 weeks from foundations to handover, including all internal fit-out. A two-storey extension may take 18–30 weeks. Design, planning, and Building Regulations approval typically add 8–16 weeks before construction begins. The most significant delay risk is obtaining planning permission, which can take 8–13 weeks for standard applications.
What qualifications should a house extension builder have?
For a house extension, look for a London builder who is a member of the Federation of Master Builders (FMB), holds a relevant CSCS card, and has verifiable experience with residential extensions. Your architect or structural engineer should supervise the build against approved drawings. All electrical work must be certified by a Part P electrician, and any gas work must be done by a Gas Safe registered engineer.
How much value does a house extension add?
A well-designed house extension typically adds 10–25% to the value of a UK property, depending on location, the quality of the work, and how well the extension integrates with the original building. Open-plan kitchen-dining extensions and master bedroom suites with en-suites tend to deliver the highest return. In premium London postcodes, an extension can add £100,000–£300,000 to property value.
Price disclaimer: All prices on this page are estimates based on 2026 UK market research and publicly available data for London and the surrounding area. Actual costs will vary according to the specific job, access requirements, materials, and your exact location within London. Always obtain at least three written, itemised quotes from qualified, insured tradespeople before committing to any work. Last verified: February 2026.
Compare Quotes from Trusted House Extension Builders in London
Connect with vetted local house extension builders and get free, no-obligation written quotes.