How much does a home extension cost in Kent in 2026? It is one of the most common questions we hear, and the honest answer is: it depends on the type, size, and specification of extension you want. But that is not particularly helpful when you are trying to budget. So here is a detailed breakdown based on the projects we have delivered across Kent over the last 20 years, updated with 2026 prices.
Extension Costs at a Glance
| Extension Type | Cost per sqm | Typical Total Cost |
|---|---|---|
| Single-storey rear (basic) | £1,500–£1,800 | £30,000–£45,000 |
| Single-storey rear (mid) | £1,800–£2,200 | £45,000–£55,000 |
| Single-storey rear (premium) | £2,200–£3,000 | £55,000–£75,000 |
| Two-storey rear | £1,400–£2,200 | £56,000–£88,000 |
| Wrap-around | £1,600–£2,500 | £56,000–£87,500 |
| Side return (terraced) | £2,000–£3,000 | £30,000–£45,000 |
| Over-garage | £1,400–£2,000 | £28,000–£40,000 |
| Orangery | £2,500–£3,500 | £50,000–£87,500 |
These figures include groundworks, structure, roofing, windows, internal finishes, electrics, plumbing, and decoration. They do not include kitchen or bathroom fittings — these vary so widely that quoting a meaningful average is misleading.
What Is Included in the Cost Per Square Metre?
When we quote an extension, our price per square metre covers:
Groundworks: Excavation, foundations (typically 1–2.5 metres deep in Kent, depending on ground conditions and proximity to trees), drainage connections, and oversite preparation.
Structural work: Steelwork for openings (RSJs), brickwork or blockwork walls, wall ties, cavity insulation, and damp-proof courses.
Roofing: Timber roof structure, felt and battens, tiles or flat roofing membrane, fascias, soffits, and guttering.
Windows and doors: Double or triple glazed units, including bifold or sliding doors where specified.
First fix: Electrical wiring, plumbing pipework, and heating connections roughed in before plastering.
Plastering and internal finishes: All walls and ceilings skimmed, ready for decoration.
Second fix: Sockets, switches, light fittings, radiators, and plumbing connections completed.
Decoration: Walls and ceilings painted (typically white emulsion as standard; upgraded finishes are priced separately).
Flooring preparation: Screeded and levelled, ready for your chosen floor finish.
Factors That Increase Costs
Ground Conditions
Kent has varied geology — London Clay around Tonbridge and Tunbridge Wells, Wealden Clay in the south, chalk in the North Downs, and alluvial deposits near rivers. Clay soils are particularly problematic because they shrink and swell with moisture changes.
Impact: Foundations in clay areas often need to be 1.5–2.5 metres deep (versus 1 metre in stable ground). Deeper foundations add £3,000–£8,000 to the groundworks cost. Properties near large trees may require piled foundations, adding £10,000–£20,000.
Structural Complexity
Removing load-bearing walls to create open-plan living requires structural steelwork. A single RSJ to support a standard opening costs £1,500–£3,000 installed. Larger openings or multiple removals can add £5,000–£15,000.
Specification and Finishes
The difference between a basic and premium extension is largely in the finishes:
| Element | Basic | Mid | Premium |
|---|---|---|---|
| Windows | Standard uPVC | Aluminium | Slim-frame aluminium |
| Doors | French doors | Bifold (3-panel) | Bifold (5-panel) or sliding |
| Flooring | Laminate | Engineered wood | Natural stone |
| Heating | Radiators | Underfloor (water) | Underfloor + zoned controls |
| Lighting | Standard pendants | Recessed downlights | Architectural lighting design |
| Kitchen | N/A | £10,000–£20,000 | £25,000–£50,000+ |
Access and Location
Restricted access (narrow side passages, no rear vehicle access) increases costs because materials must be carried by hand and waste removed manually. This typically adds 5–10% to the build cost.
Properties in conservation areas may require specific materials (handmade bricks, natural slate roofing, traditional timber windows) that cost significantly more than standard alternatives. This is common across Kent — Tonbridge, Sevenoaks, Tunbridge Wells, Hildenborough, and many rural villages have conservation designations.
Real Project Examples
Here are anonymised examples from recent Kent projects to give you a realistic picture:
Example 1: Single-Storey Kitchen Extension, Tonbridge
- Size: 22 sqm
- Spec: Mid-range — aluminium bifold doors, underfloor heating, engineered oak floor, quality kitchen
- Total cost: £52,000 (£2,364/sqm) excluding kitchen
- Kitchen: £18,000
- Build time: 14 weeks
Example 2: Two-Storey Extension, Tunbridge Wells
- Size: 38 sqm total (19 sqm per floor)
- Spec: Premium — slim-frame aluminium, natural stone floor, bespoke joinery
- Total cost: £82,000 (£2,158/sqm)
- Build time: 20 weeks
- Note: Deep foundations required due to mature oak trees, adding £6,000
Example 3: Wrap-Around Extension, Sevenoaks
- Size: 32 sqm
- Spec: Mid-to-premium — bifold doors, vaulted ceiling with rooflights, underfloor heating
- Total cost: £68,000 (£2,125/sqm) excluding kitchen
- Build time: 16 weeks
- Note: Conservation area — handmade bricks required, adding approximately £3,000
Example 4: Side Return Extension, Chislehurst
- Size: 12 sqm
- Spec: Premium — full-height glazing, polished concrete floor, bespoke steel and glass roof
- Total cost: £38,000 (£3,167/sqm)
- Build time: 10 weeks
- Note: London Borough of Bromley planning requirements
Hidden Costs to Budget For
Beyond the build cost itself, plan for these additional expenses:
| Item | Typical Cost |
|---|---|
| Architectural drawings | £2,000–£5,000 |
| Structural engineer | £500–£1,500 |
| Planning application (if needed) | £206 (standard) |
| Building Regulations fee | £400–£800 |
| Party wall surveyor (if applicable) | £700–£1,500 per neighbour |
| Drainage survey (CCTV) | £250–£400 |
| Kitchen/bathroom fittings | £5,000–£50,000+ |
| Landscaping reinstatement | £1,000–£5,000 |
| Contingency (10–15%) | Varies |
Our advice: Always budget 10–15% contingency. With older properties especially, opening up walls and floors can reveal unexpected issues that need addressing.
How to Get the Best Value
1. Be clear about your priorities: Know what matters most — size, specification, or budget. We can design to any of these priorities.
2. Get the design right first: Changes during construction are expensive. Investing properly in design and specification before building starts saves money overall.
3. Choose your builder before finalising design: An experienced builder can advise on cost-effective construction methods and materials during the design phase, before you commit to an approach that may be unnecessarily expensive.
4. Do not always choose the cheapest quote: If one quote is significantly lower than others, question what has been excluded or underspecified. We have rescued many projects in Kent where clients initially chose a cheaper contractor.
5. Consider timing: Spring and summer are the busiest periods for builders. Starting in autumn or winter (when groundworks are feasible) can sometimes offer better availability and pricing.
Financing Your Extension
Most Kent homeowners fund extensions through:
- Savings: The simplest option with no interest costs
- Remortgage: Often the cheapest borrowing rate, with the extension adding value that supports the increased mortgage
- Home improvement loan: Unsecured personal loans up to £25,000–£50,000
- Equity release: For older homeowners looking to improve their property
- Bridging finance: Short-term funding for larger projects, repaid through remortgage on completion
Important: An extension that costs £50,000 but adds £65,000 to your property value is a sound financial investment. Most extensions in desirable Kent locations deliver a positive return.
Ready to discuss your extension project? Carey Brothers & Sons provide free, detailed quotations for home extensions across Kent — from Tonbridge and Tunbridge Wells to Sevenoaks, Maidstone, Ashford, and beyond. Every quote includes a full cost breakdown with no hidden charges. Call 07879 447975 or contact us to arrange a free site visit.
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