Written by Ben, Founder of BDC Construction Ltd. 20+ years building extensions across Kent.
Last updated: September 2026
| This house extension cost calculator gives Kent homeowners a 2026 price estimate in seconds. A single-storey extension in Kent costs £2,000 to £3,000 per square metre. A typical 20m² to 30m² build lands between £50,000 and £90,000 all-in. Double-storey builds run £85,000 to £160,000. |
Most cost guides give you a vague UK-wide figure. That figure helps nobody plan a real budget. This calculator uses Kent rates from 2026, so your estimate reflects local labour and ground conditions. Below the tool, you will see what the price includes and what sits on top.
How does the house extension cost calculator work?
| The house extension cost calculator applies 2026 Kent rates to your inputs. You choose your extension type, floor area, finish level and Kent location. The tool multiplies your square metres by the right rate. It then adds VAT, fees and contingency, and returns a low to high range. |
- Extension type: single-storey, double-storey, side return, wraparound, over-garage or kitchen.
- Floor area in square metres, or width by depth.
- Finish level: basic, standard or premium.
- Kent area, since west Kent runs higher than Medway or Ashford.
- Optional toggles for VAT, professional fees and contingency.
Your result is a planning-stage range, not a fixed quote. Accuracy improves with a site visit, which accounts for your ground and access.
How much does an extension cost per m² in Kent in 2026?
| In 2026, Kent house extensions cost £1,800 to £3,300 per square metre. Single-storey rear extensions run £2,000 to £3,000 per m². Double-storey builds run £1,900 to £2,800 per m². Side returns and wraparounds run £2,200 to £3,300 per m². Kent sits 15% to 25% above UK averages. |
| Extension type | Cost per m² (Kent, 2026) | Typical total |
|---|---|---|
| Single-storey rear | £2,000 to £3,000 | £50,000 to £90,000 (20m² to 30m²) |
| Double-storey | £1,900 to £2,800 | £85,000 to £160,000 (40m² to 60m²) |
| Side return | £2,300 to £3,300 | £25,000 to £45,000 (6m² to 12m²) |
| Wraparound | £2,200 to £3,200 | £70,000 to £110,000 (25m² to 40m²) |
| Over-garage or first floor | £1,800 to £2,500 | £40,000 to £65,000 (20m² to 30m²) |
Kent rates sit above the national picture. UK single-storey extensions average £1,800 to £3,000 per square metre in 2026, according to RICS BCIS and MyJobQuote data. Kent labour competes with London, and rural delivery adds cost. Central London still runs 20% to 30% higher than Kent.
Note: these figures cover the shell build with a standard finish. They exclude VAT, professional fees and kitchen fittings.
How much does a single-storey extension cost in Kent?
| A single-storey rear extension in Kent costs £2,000 to £3,000 per square metre in 2026. A 20m² kitchen-diner lands around £50,000 to £65,000 all-in. A 25m² build runs £58,000 to £78,000. A 30m² build runs £68,000 to £90,000. |
Typical single-storey extension costs in Kent for 2026:
- 15m² rear extension: £32,000 to £48,000
- 20m² rear extension: £50,000 to £65,000
- 25m² rear extension: £58,000 to £78,000
- 30m² rear extension: £68,000 to £90,000
Standard quotes cover foundations, steels, brickwork, roof, windows, doors, electrics, plastering and decoration. They exclude kitchen units, appliances, landscaping and VAT. Most single-storey projects take 12 to 18 weeks on site. See our full Kent house extension cost guide for a line-by-line breakdown.
How much does a double-storey extension cost in Kent?
| Double-storey extensions in Kent cost £1,900 to £2,800 per square metre in 2026. A 40m² two-storey build typically runs £85,000 to £115,000 all-in. It is not double the price of a single storey. A double-storey usually costs 50% to 70% more, because the foundations and roof are shared. |
Going up costs less per square metre than going out. You share the foundations and roof across two floors. That spreads the fixed costs over more space.
Total costs still run higher, because you add more floor area. Scaffolding, extra steels and upstairs plumbing push the bill up. Two-storey builds almost always need full planning permission. A semi or terrace will also need a party wall agreement.
Timelines run 20 to 30 weeks on site, reflecting more structural work and more finishing.
How much does a kitchen, side return or wraparound extension cost in Kent?
| Kitchen extensions in Kent add £15,000 to £35,000 on top of the shell build in 2026. That covers units, worktops and appliances. Side return extensions cost £2,300 to £3,300 per square metre. Wraparound extensions cost £2,200 to £3,200 per square metre. |
Kitchen extensions
Units, worktops and appliances add most of the kitchen cost. Mid-range kitchens run £10,000 to £15,000. High-end kitchens exceed £25,000. Budget £3,000 to £6,000 for installation and new plumbing runs.
Side return extensions
Side return extensions cost £2,300 to £3,300 per square metre in Kent. Totals run £25,000 to £45,000 for a 6m² to 12m² build. They suit Victorian terraces in Tunbridge Wells and Tonbridge. The higher rate reflects fixed costs spread over fewer square metres.
Wraparound extensions
Wraparound extensions cost £2,200 to £3,200 per square metre in Kent. Totals run £70,000 to £110,000 for a 25m² to 40m² build. An L-shaped layout combines rear and side space. Value per square metre improves once you pass 25m².
What does an extension quote include, and what is excluded?
| An extension build quote in Kent covers foundations, steels, brickwork, roof, windows, doors, electrics, plumbing, plastering and decoration. It excludes VAT at 20%, professional fees, kitchen fittings, landscaping and contingency. On a £70,000 build, these extras can add £12,000 to £25,000 to your final total. |
| Included in the build quote | Usually excluded |
|---|---|
| Foundations and groundworks | VAT at 20% |
| Structural steels | Architect and engineer fees |
| Brickwork and roof | Kitchen units and appliances |
| Windows and external doors | Party wall surveyor fees |
| Electrics and plumbing | Landscaping and driveways |
| Plastering and decoration | Contingency (10% to 15%) |
Value Added Tax applies at 20% on domestic extension work, as set by HMRC. Always check whether a quote is VAT-inclusive. Professional fees add another 7% to 15% of the build cost. A party wall surveyor costs £700 to £1,200 per neighbour.
Do you need planning permission for an extension in Kent?
| Many single-storey extensions in Kent fall under permitted development. A rear extension up to 3m for attached homes, or 4m for detached, usually qualifies. Building Regulations approval is always required. Conservation areas and Article 4 directions often remove permitted development rights. England’s householder planning fee is £548 from April 2026. |
Permitted development is a set of rights that allow certain building work without a full planning application. An Article 4 direction is a rule that removes those rights in a named area. Building Regulations are the mandatory standards for a safe, habitable extension.
Around 25% of Kent lies within the Kent Downs or High Weald National Landscapes. Many towns add conservation area status on top. In those areas, an Article 4 direction can force a full planning application.
England’s householder planning application fee is £548 from 1 April 2026, according to the Planning Portal. Listed buildings need Listed Building Consent, which can add 8 to 16 weeks and £5,000 to £15,000. Always check your address on the official Planning Portal before you commission drawings.
How accurate is a house extension cost calculator?
| House extension cost calculators give a reliable budget range, not a fixed price. They apply typical Kent rates to your size, type and finish. They cannot see your ground conditions, access or structural needs. Expect the real figure to land within the range shown. A site survey gives you a fixed quote. |
Our ranges come from real Kent projects, not scraped averages. That experience shows where budgets actually move. Clay soil across the Kentish Weald often needs deeper foundations. A narrow rural lane can slow every delivery and add labour hours.
According to Ben, founder of BDC Construction, in September 2026:
“The two things that move a Kent quote most are the ground and the access. A build on clay in the Weald, down a tight lane, prices very differently from a level plot. A calculator sets your expectation. A site visit sets your price.”
Get an itemised quote for your Kent extension
Extending a Kent home in 2026 is a large but predictable spend. Your cost depends on type, size, finish, ground conditions and location. Use the calculator above to set a realistic range, then confirm it with an itemised quote.
BDC Construction has built extensions across Kent for more than 20 years. For a fixed, itemised quote based on your actual property, call 01622 946189 or request a free site visit.
What size extension are you planning, and does your Kent budget match the range above?