How much does a single storey extension cost in Kent?

For 2026, a standard single storey extension in Kent typically costs £2,200–£3,200 per m² for a mid-spec build. A 20m² rear extension usually lands between £44,000 and £64,000 before VAT, kitchens or finishes.

How much does a double storey extension cost?

Double storey extensions cost roughly 50% more than a single storey of the same footprint — typically £3,000–£4,200 per m² in Kent, because you gain a second floor without doubling the foundations or roof.

What's included in the per m² price?

A mid-spec per m² rate normally covers structural shell, roof, windows and doors, plastering, basic electrics and plumbing first fix. Kitchens, bathrooms, premium glazing, landscaping and VAT are usually quoted separately.

Do I need planning permission for an extension in Kent?

Many single storey rear extensions fall under Permitted Development, but conservation areas, listed buildings and larger projects in Maidstone, Tunbridge Wells and Sevenoaks often require full planning. We help clients check this before quoting.

House Extension Cost Guide (Kent) — 2026 Prices

Wondering how much a house extension actually costs in Kent in 2026? This guide gives you realistic per-square-metre rates, a worked example, the factors that move the price up or down, and a simple way to sanity-check any quote you receive — written by a builder, not a comparison site.

House extension cost per m² in Kent (2026)

For a mid-spec build by a reputable Kent contractor, expect the following ballpark rates before VAT and before kitchen / bathroom fit-out:

Single storey extension: £2,200 – £3,200 per m²
Double storey extension: £3,000 – £4,200 per m²
Wrap-around extension: £2,600 – £3,700 per m²
Loft conversion: £1,800 – £2,800 per m²

Kent and the South East typically run 10–15% higher than UK averages because of labour and material logistics. Properties inside the M25 fringe (Sevenoaks, Westerham, Dartford) sit at the top of these ranges.

Extension cost calculator — by project type

Quick reference table. Figures exclude VAT, kitchens, premium glazing and landscaping.

Project	Typical size	Low	High	Notes
Single storey rear extension	20 m²	£44,000	£64,000	Most common Kent project — kitchen-diner add-on.
Single storey rear extension	30 m²	£66,000	£96,000	Open-plan with bi-fold doors.
Side return extension	12 m²	£28,000	£42,000	Victorian terrace infill, common in Tunbridge Wells.
Double storey extension	30 m² footprint	£90,000	£126,000	Adds bedroom + ensuite above kitchen extension.
Wrap-around extension	35 m²	£90,000	£130,000	Side return + rear combined.
Kitchen extension (mid-spec)	25 m²	£60,000	£85,000	Includes kitchen units & worktops at mid-range.
Garage conversion	18 m²	£18,000	£32,000	Existing shell — cheapest route to extra space.
Loft conversion (dormer)	25 m²	£45,000	£70,000	Adds bedroom + bathroom under the roof.

Worked example: 25 m² single storey kitchen extension

A typical Maidstone semi-detached client adding a 25 m² rear kitchen extension with bi-fold doors and underfloor heating, mid-spec finishes:

Shell, roof, glazing, electrics, plumbing first fix: ~£62,500 (£2,500/m²)
Kitchen units & worktops (mid-range): ~£14,000
Tiling, flooring, decoration: ~£6,500
Architect & structural engineer: ~£3,500
Building Control & planning fees: ~£1,200
Contingency (10%): ~£8,800

All-in budget: ~£96,500 + VAT. This is a representative 2026 figure for Kent — your own quote could be 15% lower or 25% higher depending on access, ground conditions and specification.

What moves the price up or down?

Ground conditions — clay or sloping sites push foundations up by £4k–£10k

Glazing — bi-folds and slim aluminium double the window line cost

Kitchen spec — £6k vs £30k is the single biggest variable

Steel beams — open-plan layouts add £3k–£8k in structural steel

Access — tight side returns add labour days for material handling

Listed buildings & conservation areas — bespoke materials & approvals

VAT — most domestic extensions are 20% standard rated

Finishes — engineered oak vs laminate, porcelain vs ceramic

Red flags in a quote

Quotes more than 25% below the ranges above — almost always missing scope.

No itemised breakdown — you can't compare like-for-like.

Large deposits before any work starts — 10–15% on materials is reasonable; 50% isn't.

No written specification — verbal "mid-range kitchen" means nothing on a contract.

How long does an extension take in Kent?

Single storey rear extension: 12–16 weeks on site
Double storey extension: 16–22 weeks
Wrap-around extension: 18–24 weeks
Loft conversion: 8–12 weeks

Add 8–14 weeks beforehand for design, planning and Building Regulations approvals — longer if you're in a conservation area in Tunbridge Wells, Sevenoaks or central Maidstone.

FAQs

Is it cheaper to extend or move?

In most of Kent, a £80–£120k extension adds £100–£180k to your property value and avoids ~£20k of stamp duty and moving costs. Extending almost always wins unless you've outgrown the plot.

Do I need an architect?

For anything over ~15 m² or any structural change, yes. Architectural fees of 8–12% of the build cost pay for themselves in planning success and avoided on-site changes.

Can I live in the house during the build?

Yes for most rear extensions — we'll seal the existing wall until the final break-through. Wrap-arounds and loft conversions disrupt more.

What about Permitted Development?

Many single storey rear extensions up to 6m (detached) or 4m (semi/terraced) fall under PD, but you still need a Lawful Development Certificate and Building Regs approval.

House Extension Costs in Kent