SBP-logo
Contact Us
Updated January 2026 — UK & London Rates

Free Construction
Calculator Hub

Use our free construction cost calculator London to estimate any project in 2026. House extensions, loft conversions, new builds, refurbishments, stamp duty, bricks and concrete — all London-adjusted, all free, with instant results and no sign-up required.

✓ 2026 Rates
✓ London Adjusted
✓ Instant Results
✓ No Sign-Up
7Calculators
300+Projects Done
15+Years Exp.
FreeConsultation

Free Construction Cost Calculator — London & UK 2026

Our free construction cost calculator London tool is the UK's most comprehensive builder's pricing guide for 2026. Whether you need a free building cost calculator for a house extension, loft conversion, new build or refurbishment — or a stamp duty calculator for your next property purchase — every tool on this page gives you instant, London-adjusted results with no registration required. Furthermore, all tools are updated quarterly against live tender returns and BCIS data.

Each calculator adjusts for your location, build quality and project specification. As a result, you can walk into any contractor conversation knowing your rough budget before a single quote arrives. In addition, our stamp duty calculator covers SDLT, LBTT and LTT — so buyers across England, Scotland and Wales are covered.

Moreover, our brick and concrete calculators help tradespeople and self-builders work out exact material quantities, including wastage allowances. Simply select your calculator below, fill in your project details and get an instant result. No sign-up. No cost. Just honest numbers.

Select your project type using the tabs below. Our house extension cost calculator covers single and double storey rear extensions, side returns and wrap-arounds. The loft conversion cost calculator covers Velux, dormer, hip-to-gable and mansard types. Use the Total Project Cost toggle below to see your real all-in budget including VAT, professional fees and contingency. Rates reflect 2026 London and UK market pricing. For expanded FAQs and more detail, see our dedicated house extension cost calculator and loft conversion cost calculator pages.

📊 What would you like to see?
Build Cost Only — what your builder charges for construction. Excludes VAT, professional fees and contingency.
Total Project Cost — your real all-in budget. Adds 20% VAT + 10% professional fees + 10–15% contingency. Research shows total project cost is typically 40% above build cost.
Floor Area
30 m²
5m²50m²100m²150m²200m²
Estimated Build Cost
Select options
Fill in all fields for an instant estimate
2026 BCIS-aligned rates. Build Cost view excludes VAT, fees & contingency. Switch to Total Project Cost above to see your real all-in budget. Always get a written quote.
📋 Get a Free Quote 📞 +44 7404 931629
Usable Floor Area
30 m²
10m²25m²40m²60m²80m²
Estimated Build Cost
Select options
Fill in all fields for an instant estimate
Includes structural, roofing, insulation, windows, plasterwork & basic fit-out. Switch to Total Project Cost above to include VAT, fees and contingency.
📋 Get a Free Quote 📞 +44 7404 931629
Total Floor Area
80 m²
20m²100m²200m²350m²500m²
Estimated Cost
Select options
Fill in all fields for an instant estimate
Assumes typical 1970s–2000s UK residential. Structural, damp-proofing and asbestos removal costs are additional where required.
📋 Get a Free Quote 📞 +44 7404 931629
Total GIA Floor Area
120 m²
40m²150m²300m²450m²600m²
Estimated Build Cost
Select options
Fill in all fields for an instant estimate
Excludes land, planning, architect & engineer fees. Substructure varies by site conditions. VAT at 20% — self-build may qualify for zero-rating.
📋 Get a Free Quote 📞 +44 7404 931629

Our free stamp duty calculator 2026 covers SDLT (England and Northern Ireland), LBTT (Scotland) and LTT (Wales). Calculate stamp duty for first-time buyers, home movers, buy-to-let purchases and limited company acquisitions. Rates reflect the changes introduced on 1 April 2025. Enter your purchase price below for an instant banded breakdown.

Rates shown are effective from 1 April 2025. The temporary SDLT nil-rate band increase ended 31 March 2025. Standard rates have reverted. Always confirm with your solicitor before exchange. For official guidance visit GOV.UK Stamp Duty Land Tax ↑.
Stamp Duty / Land Tax
Enter price
Enter a purchase price to calculate
SDLT is payable within 14 days of completion. First-time buyer relief applies on purchases up to £500,000. Additional property surcharge is +5% on all bands.
📋 Free Property Consultation 📞 +44 7404 931629

Our free brick calculator UK works out how many bricks or blocks you need for any wall. Standard half-brick walls use 60 bricks per m². Full brick walls need 120 bricks per m². Concrete blocks use 10 per m². Enter your wall dimensions and openings below — the calculator automatically deducts windows and doors and includes mortar quantities with a 5% wastage allowance. For expanded FAQs, reference tables and ordering tips, see our dedicated brick calculator UK page.

A standard house brick is 215×102.5×65mm with a 10mm mortar joint. Thermalite/Aircrete blocks are 440×215×100mm. All quantities include 5% wastage allowance.
Materials Required
Enter dimensions
Enter wall dimensions to calculate
Quantities include 5% wastage. Premixed mortar 1 tonne bag lays approximately 1,000 standard bricks. Order from the same batch to ensure colour consistency. Always allow extra for cutting on corners and reveals.
📋 Free Site Survey 📞 +44 7404 931629

Our free concrete mix calculator tells you exactly how much cement, sharp sand and 20mm aggregate you need for any pour. Choose your concrete mix ratio — C10, C20, C25 or C30 — and get results in 25kg bags or bulk tonnes. All quantities include a 10% overage allowance. Enter your slab or foundation dimensions below. For a detailed grade guide, mixing tips and FAQ, see our dedicated concrete mix calculator UK page.

Path 75mm · Slab 100mm · Foundation 300mm+
For pours over 1.5m³ we strongly recommend ordering ready-mixed concrete. It is more consistent and typically more cost-effective than site-mixing. Water/cement ratio should be 0.45 to 0.55 for structural work. Mix design is based on BS EN 206 ↑ concrete specifications.
Materials Required
Enter dimensions
Enter dimensions to calculate quantities
Quantities include 10% overage. Mix concrete in small batches to maintain consistency. Use approximately 0.5 litres of water per kg of cement. Do not add excess water as it weakens the mix significantly.
📋 Free Project Advice 📞 +44 7404 931629
2026 Cost Reference

UK Build Cost Per m² Guide — London & Regions 2026

Typical cost-per-square-metre ranges for common construction projects. London commands a 15 to 30% premium over UK averages. All figures exclude VAT, architect fees and planning costs.

🏠

House Extension Cost

£2,300 – £4,000/m²

Single storey rear extension London 2026. Inner London 15 to 25% above outer boroughs. Side return and wrap-around extensions from £2,850/m².

🏗️

Loft Conversion Cost

£2,400 – £3,100/m²

Dormer loft conversion from £72k. Mansard from £100k. L-shaped dormer from £80k. Listed building and conservation area premiums apply.

🔨

Refurbishment Cost

£620 – £1,900/m²

Minor cosmetic refurb from £620/m². Extensive full-strip refit up to £1,900/m². Average 3-bed full refurb costs £52,000 to £125,000 in London.

🏢

New Build Cost

£2,600 – £5,800/m²

New build cost per m² from £2,300 in lower-cost UK regions. Inner London high-spec builds exceed £5,800/m² for bespoke finishes.

Know Your Numbers

What Is Included in These Estimates?

Understanding what is and is not covered ensures your project budget is accurate from day one. Furthermore, knowing what to budget separately helps avoid surprises once work starts.

✅ Included in Estimates

  • ✓Foundations, groundworks & drainage
  • ✓Structural frame, walls & roof structure
  • ✓Windows, external doors & glazing
  • ✓Insulation & airtightness measures
  • ✓First & second fix carpentry and joinery
  • ✓Plumbing & heating (standard specification)
  • ✓Electrical first & second fix
  • ✓Plastering, screeding & floor finishes
  • ✓Decoration (2-coat paint throughout)
  • ✓Mid-range kitchen & bathroom units (where selected)

❌ Excluded — Budget Separately

  • ✗Land purchase & legal/conveyancing fees
  • ✗Architect & planning consultant fees (£3,000 to £15,000+)
  • ✗Structural engineer fees (£1,000 to £5,000)
  • ✗Planning application & building regs fees
  • ✗VAT at 20% on most construction works
  • ✗Party wall surveyor costs where required
  • ✗Bespoke fitted furniture & wardrobes
  • ✗Landscaping, drives & external works
  • ✗Utility connection & diversion costs
  • ✗10 to 15% contingency buffer (always add this)
Common Questions

Construction Calculator FAQs

Answers to the most commonly searched questions about UK build costs, stamp duty, bricks, blocks and concrete mixes in 2026.

In 2026, a standard single storey rear extension costs £2,300 to £4,000 per m² in London, excluding VAT. A 25m² rear extension in outer London costs approximately £58,000 to £100,000. In inner London, the same project costs £68,000 to £120,000. Double storey extensions add 15 to 25% to the base m² rate. All figures exclude architect fees, planning costs and VAT.
A rear extension in London costs £58,000 to £120,000 for a typical 25m² single storey in 2026, depending on location and specification. At standard spec in outer London, expect around £68,000 to £78,000 all-in. High-spec inner London projects can reach £95,000 to £120,000. These costs include structural, roof, windows, electrics, plumbing and plastering but exclude architect fees, planning and VAT.
Loft conversions in London typically cost £2,400 to £3,100 per m² for a good-quality finish in 2026, before bathrooms. A standard 30m² dormer in outer London costs approximately £72,000 to £96,000. Mansard conversions in inner London start from £100,000 and frequently exceed £140,000. Velux-only conversions start from around £42,000 for a basic 30m² in outer London. An en-suite adds £8,600 to £14,200. Use our loft conversion cost calculator above for a personalised estimate.
UK building costs per m² in 2026 vary significantly by project type and region. Typical ranges are: Extensions £1,900 to £4,000/m², Loft conversions £1,600 to £3,400/m², Refurbishment £620 to £1,900/m², New build houses £1,900 to £5,800/m². London commands a 15 to 30% premium over the UK average. All figures exclude VAT, professional fees and land costs.
A new build house costs £1,900 to £2,600/m² for standard specification in lower-cost UK regions in 2026. In the South East and outer London, expect £2,300 to £3,400/m². Inner London and high-specification builds range from £3,200 to £5,800/m². A typical 120m² 3-bed self-build in outer London costs approximately £275,000 to £408,000, covering construction only and excluding land, design fees and VAT.
From 1 April 2025, a home mover buying a £300,000 property pays £5,000 in SDLT. This breaks down as 0% on the first £125,000 giving £0, 2% on the next £125,000 giving £2,500, and 5% on the final £50,000 giving £2,500. A first-time buyer pays £0 as the property falls under the £300,000 FTB nil-rate threshold. A buy-to-let buyer pays £20,000 due to the 5% additional dwelling surcharge applied across all bands. These rates remain in effect throughout 2026.
In 2026, first-time buyers pay 0% on the first £300,000 and 5% on the portion from £300,001 to £500,000. Properties over £500,000 receive no first-time buyer relief. For example, a £450,000 purchase results in 0% on £300,000 and 5% on £150,000, giving a total SDLT bill of £7,500. First-time buyer relief is unavailable if either buyer has previously owned property anywhere in the world. These rates were set on 1 April 2025 and remain current.
A standard UK brick is 215×102.5×65mm. With a standard 10mm mortar joint, a half-brick wall (102.5mm) uses 60 bricks per m². A full-brick wall (215mm) uses 120 bricks per m². Lightweight concrete blocks (440×215×100mm) use 10 blocks per m². Always add at least 5% for wastage, cuts and breakages. Order from the same batch to ensure colour consistency across the job.
For a garden path or patio, use C20 mix (1:2:4) at 75 to 100mm depth. For a driveway with car loading, use C25 (1:1.5:3) at 100 to 150mm. For heavy vehicle loading, C30 (1:1:2) at 150mm minimum is required. For house foundations, use C25 or C30 at the depth specified by your structural engineer. Never use C10 lean mix for any load-bearing application.
Order ready-mixed concrete for any pour over 1.5m³. It is more consistent, faster and usually more cost-effective at that scale. Ready-mix is also preferable where access allows and for time-sensitive pours in hot weather or for large slabs. For small DIY jobs under 1m³, bagged concrete or site-mixing with a mixer is perfectly practical. In London, ready-mixed concrete typically costs £120 to £195/m³ depending on grade and supplier.
A side return extension in London costs £3,500 to £5,500 per m² in 2026 — significantly more than a standard rear extension. The premium reflects the structural complexity: removing the original outrigger wall requires a heavy steel goalpost frame, access to the side return is typically very restricted, all materials must be carried through the house, and drainage diversions are almost always required. A typical 10m² side return in outer London costs £35,000 to £55,000 for the structure alone, before kitchen or fitting costs.
The total cost of a house extension is typically 40% higher than the builder's quote. On a £100,000 build cost, you should budget approximately: £10,000 contingency (10%), £20,000 VAT at 20%, and £10,000 professional fees at 10% — bringing the total to £140,000. Professional fees cover architect drawings, structural engineer calculations, building control fees and planning application costs. Use our Total Project Cost toggle above to see the all-in figure for your specific project.
Professional fees for a residential extension or loft conversion typically total 8% to 15% of the build cost. This covers: architect fees (£3,000–£15,000 for a standard package, or 8–12% for full service), structural engineer (£800–£2,000 for most extensions), building control fees (£700–£1,400), and planning application fees (£548 for a standard householder application in England from April 2026 — fees are now indexed to inflation annually). For a £80,000 extension, allow £8,000 to £12,000 for fees on top of the construction cost.
The Community Infrastructure Levy (CIL) is a charge levied by local authorities on new development to fund local infrastructure. For residential extensions, most homeowners are exempt from CIL if the development is self-contained (not a new dwelling) and does not create additional homes. However, new build dwellings attract CIL. Rates vary significantly by borough — in Kensington and Chelsea the 2026 rate can reach £890 per m², while Outer London boroughs typically charge £20–£50 per m² for the Mayoral CIL on top. Always confirm CIL liability with your local planning authority or architect before starting.
A mansard loft conversion in London typically costs £100,000 to £160,000+ in 2026 for a standard 30–35m² conversion. Mansards involve completely removing the existing roof and rebuilding it as a new storey with near-vertical (70-degree) walls, creating the maximum possible headroom and floor area. They almost always require formal planning permission, raise party walls on both sides, and carry party wall surveyor costs of £1,000 to £3,000 per affected neighbour. Inner London mansards in conservation areas can reach £200,000+ once all fees are included.
A dormer loft conversion projects vertically out from the existing sloping roof, adding a box-shaped addition with a flat roof. The majority of the original roof structure is kept. Dormers typically fall within permitted development rights and do not require planning permission. A mansard conversion replaces the entire roof structure, creating a new near-vertical wall and flat roof. This gives significantly more headroom and floor area than a dormer, but always requires planning permission, costs considerably more, and takes longer to build. In London, dormers are the most common choice for mid-terraced properties; mansards are typically used on end-of-terrace or detached properties where planning permission is more readily granted.
More Information

How to Use These Construction Cost Calculators

All results are indicative estimates based on 2026 London and UK rates. Furthermore, every project is different and site-specific factors can affect the final cost. Therefore, always follow up with a written quote from a qualified contractor before committing to a budget.

🏠 Build Cost Calculator

Our house build cost calculator uses 2026 BCIS-aligned cost-per-m² rates adjusted for your location, quality and project type. It covers rear extension costs, loft conversion costs per m², full house refurbishment and new build cost estimates. Results are typically accurate to plus or minus 15 to 20% and are best used as a feasibility guide before getting written quotes. For a fully dedicated tool with expanded FAQs, see our house extension cost calculator and loft conversion cost calculator.

💷 Stamp Duty Calculator 2026

Our SDLT calculator is updated with the rates effective from 1 April 2025 which remain in force throughout 2026. The nil-rate band reverted to £125,000 for standard buyers and £300,000 for first-time buyers. Moreover, we cover all buyer types including first-time buyer stamp duty, home movers, buy-to-let stamp duty, additional properties and limited company purchases in England, Scotland and Wales.

🧱 Brick & Concrete Calculators

Our brick calculator tells you how many bricks per m² you need. Half-brick walls use 60, full-brick walls use 120, and lightweight blocks use 10 per m². Our concrete calculator works out cement, sand and aggregate for C10 to C30 mixes based on BS EN 206 mix design ratios. In addition, both tools include wastage allowances and can output results in bags or bulk tonnes. See our dedicated brick calculator UK and concrete mix calculator UK pages for expanded guides.

About Our Construction Cost Calculators — UK & London 2026

All construction cost calculators on this page are maintained by Signature Build Properties, a London-based design and build contractor with 15+ years of experience across all London boroughs. Rates are reviewed quarterly against BCIS data, Federation of Master Builders surveys and live tender returns. As a result, our figures reflect current market conditions for 2026.

Our extension cost calculator London uses base rates of £2,300 to £4,000/m² with location multipliers for inner London, outer London and UK regions. Our stamp duty calculator reflects the April 2025 rate changes in full, including the reverted nil-rate bands and the 5% additional dwelling surcharge, which remain in force throughout 2026. Furthermore, our material calculators are based on BS EN 771-1 standard brick dimensions and BS EN 206 concrete mix design ratios.

If you would like a fixed-price quote for your project, our team covers Hayes, Ealing, Hounslow, Richmond upon Thames and Surrey. Contact us for a free site visit with no obligation.

Ready to Start Your Project?

Free Consultation
For Any Build Project — London Wide

Our design and build team will visit your property, assess the scope and provide a detailed fixed-price quote. No obligation. All London boroughs covered from our Hayes base.

📋 Book Free Consultation 📞 +44 7404 931629
✓Free consultation
✓Fixed-price quote
✓Design & build
✓All London boroughs
✓Reply within 24hrs
Signature-Build-footer-logo

Get In Touch

Contact us today to discuss your project and receive a no-obligation quote.

Contact Information

149 Ashford Ave, Hayes UB4 0ND, UK
contactus@signaturebuildproperties.co.uk
+44 7404 931629
Instagram X-twitter
© 2026 All Right Reserved Built Digitally