How much does a house extension
in Kent cost in 2026?

For many homeowners, the thought of an extension starts with the realisation you're outgrowing your home

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Perhaps your kitchen feels too small for the demands of family life. Or maybe you're working from home more often and the "office" in the spare isn't cutting it.

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Whatever the reason, one of your first questions will be "how much will it cost?"

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It's a question we get asked often. The honest answer is it depends, based on the type, size and specification of your project. We know that's not helpful on its own – so in this guide we'll give you some general figures, explain what drives costs up and down, and help you build a realistic picture of what your project might involve.

What does a house extension cost in Kent in 2026?

The South East typically adds 20 to 40 per cent to national average build costs. This means that as a Kent homeowner, you should work from figures that reflect local labour and material rates rather than national headlines.

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As a general guide, here are typical all-in investment ranges for the most common extension types in Kent:

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​​​​​​​​​​Important notes on these figures:

• All ranges are inclusive of VAT at 20%. Most builder quotes are stated ex-VAT, so always add 20% to headline figures when you're comparing

• Ranges reflect standard to premium specification. A basic finish with uPVC glazing and a standard kitchen will sit at the lower end; aluminium bi-fold doors, a roof lantern, underfloor heating and a bespoke kitchen will sit toward the upper end

• Ranges include groundworks, structure, roof, first and second fix, and basic internal finishes. They don't include kitchen units or appliances unless stated

• Professional fees (architect, structural engineer, planning, building control) are additional – see below

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Cost per square metre in Kent

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The average house extension cost per m² in the UK in 2026 is £2,200–£3,200 for a single-storey rear extension at national rates. As we've touched upon, prices in Kent and the wider South East are higher. A practical working range is:

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​​​​​All figures exclude VAT and professional fees.

Larger extensions have a lower cost per m² because fixed costs – foundations, roof structure, scaffolding hire, skip hire – are spread over more floor area. A 10 m² extension might cost £2,200/m², while a 30 m² extension of the same spec could come in at £1,700/m². The same principle applies at Kent rates: building bigger is proportionally cheaper per square metre.

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Professional fees: the costs homeowners most often overlook

Something to remember is build costs are only part of the picture. Your project budget also needs to account for professional and statutory fees, which typically add 12–15% on top of construction costs:

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​For a £100,000 extension, this means a realistic all-in budget – including VAT and fees – is closer to £120,000–£125,000.

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Why two similar extensions can cost very different amounts

Two extensions of a similar footprint can carry very different price tags, so understanding why will help you avoid any surprises.

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Ground conditions: These are one of the most significant variables. Clay soils (common in parts of Kent), high water tables, tree roots near the foundation zone, or a sloping plot all increase the cost and complexity of groundworks. This is something your builder should investigate before quoting.

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Structural requirements:  Again, requirements vary considerably. A simple box extension with a flat or lean-to roof needs less structural steelwork than a wide-span open-plan space with large glazed openings. The more steel involved, the higher the cost.

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Specification choices:  Your specs will have a large cumulative effect. Add bi-fold doors (£3,000–£6,000), underfloor heating (£50–£80 per m²), a roof lantern (£1,500–£3,500), and a fitted kitchen (£8,000–£20,000+) and the per-metre cost can double.

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Access: How easy it is to access your property matters more than you might expect. Builders will need easy access to the work site for tools and machinery – tight access means more manual labour and higher costs. Many properties in Sevenoaks, Tonbridge and Tunbridge Wells have restricted rear access, which can add meaningfully to groundwork and materials costs.

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Conservation areas: Areas of outstanding natural beauty (AONBs) and conservation areas are particularly relevant in Kent. Tunbridge Wells and Sevenoaks sit largely within the High Weald and Kent Downs AONB, where permitted development rights are restricted. If your property sits within one of these areas, you'll likely need full planning permission rather than the simpler permitted development route. Factor his into the time and cost of the design and approval process.

Is it better to extend or move?

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This is a most common conversations we have with our prospective clients. Moving might seem like the obvious solution – but once the full cost of a move is calculated honestly, extending often makes more financial sense. Let's look at the numbers:

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That £35,000–£80,000 is money spent before a single improvement is made to your new home. For many families, it represents a significant proportion of what an extension would cost – and an extension also means staying in a neighbourhood you already know, close to the schools, friends and community you've built around you.

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What does a well-specified extension add to your home's value?

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In 2026, a well-executed house extension will add around 10–20% to your property value. Expressed in a different way, that's a typical return of £1.20–£1.50 for every £1 spent at current South East property values.

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Given average property values in Sevenoaks are £550,000–£700,000, while in Tunbridge Wells they're £450,000–£550,000, a 10–15% uplift represents a significant financial return alongside the benefit to your lifestyle.

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In our experience, the extensions that consistently deliver the strongest combined lifestyle and financial return are:

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Open-plan kitchen-diner extensions: These remain the most sought-after improvement among Kent homeowners. Creating a connection between the kitchen, dining area and garden transforms how a family uses their home day-to-day. This type of extension is consistently cited by estate agents as one of the highest-value improvements in the South East market.

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Double-storey extensions: These offer excellent value for money per square metre. By adding both ground-floor living space and first-floor bedrooms in a single project, they avoid the fixed costs of groundworks and scaffolding being incurred twice. For growing families who need both space and bedrooms, this type of extension is an efficient use of your budget.

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Rear extensions with garden connection: We've seen a demand for more indoor-outdoor living, particularly those extensions that also incorporate rooflights, structural glazing or roof lanterns. Our Mellows project is a good example of what's achievable: a glass apex rooflight flooding a new kitchen-diner with natural light, connected to a landscaped patio below.

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Planning permission and permitted development in Kent

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One of the first practical questions you need to ask is whether your extension needs full planning permission, or can be built under permitted development rights.

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Permitted development (PD) rights allow certain types of work without a formal planning application. For detached houses, rear extensions can extend up to 4 metres under standard permitted development, or up to 8 metres under the Prior Approval Neighbour Consultation Scheme. For semi-detached and terraced houses, the limits are 3 metres under standard PD, and up to 6 metres under Prior Approval.

However, Kent is split across 12 local planning authorities. Each authority applies the national rules within a local context. Parts of the Tunbridge Wells and Sevenoaks areas sit within the High Weald AONB, where permitted development rights are restricted. Similarly, conservation areas in Kent villages such as Brenchley, Matfield and Goudhurst can carry additional constraints. In practice, this means:

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• Most standard rear extensions on houses not in a conservation area or AONB can proceed under Permitted Development, subject to size limits

• Extensions in Sevenoaks and Tunbridge Wells should be checked carefully before assuming PD applies – AONB restrictions are commonly overlooked

• Any extension over the PD size limits, or in a listed building, will require a formal planning application – currently £528 for a householder application in England

• Always check with your local Kent council before committing to a design

At Reeve Renovations, our approach is to guide you through this process from the outset, helping you understand what's possible before significant time or money is invested in detailed drawings.

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What to budget: three realistic scenarios

To make this guide more concrete, here are three worked examples of the type of projects we regularly undertake across Kent:

Scenario 1: Family bathroom and kitchen extension, Tonbridge

A single-storey rear extension of 18 m² creating a new kitchen-diner, plus a full bathroom renovation upstairs. Standard to mid-range spec, permitted development, no structural complications. Typical all-in budget, inc. VAT and fees: £90,000 – £115,000.

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Scenario 2: Rear kitchen extension with rooflights, Tunbridge Wells

A 25 m² rear extension creating an open-plan kitchen-diner-living room with a roof lantern and bi-fold doors. Mid-range spec. Planning application required (conservation area). All-in inc. VAT, fees and kitchen fit-out: £120,000 – £160,000.

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Scenario 3: Double-storey side and rear extension, Sevenoaks

A double-storey side extension adding a ground-floor playroom and utility room, plus two first-floor bedrooms and an en-suite. Similar in scope to our Hawes Lane project. Full planning permission. All-in inc. VAT and fees: £175,000 – £250,000.

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Frequently asked questions

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Is £100,000 enough for a house extension in Kent?
Yes, at £100,000 you can achieve a well-specified single-storey rear extension of around 20–25 m² with a good standard of finish. If you're hoping to include a full kitchen fit-out with premium appliances, a larger floor area, or structural glazing, a budget of £120,000–£140,000 gives you more flexibility. We'll always tell you honestly what your budget can realistically achieve.

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Do quotes include VAT?
Most builder quotes in the UK are stated excluding VAT. Always check, and remember to add 20% to any figure stated ex-VAT. A quote of £80,000 excluding VAT is £96,000 once VAT is added – a significant difference.

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How long does a house extension take in Kent?

A single-storey extension of standard complexity typically takes 12–18 weeks on site from groundworks to completion. A double-storey extension runs closer to 20–28 weeks. Planning and design work ahead of a start on-site typically adds 3–6 months to the overall programme, depending on whether planning permission is required.

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Can I live in my home during the build?
In most cases, yes. We plan the programme deliberately to minimise disruption, and most of our clients remain in their homes throughout. The period when the kitchen is out of use tends to be the main practical challenge – we'll advise you on this before work starts, and help you plan accordingly.

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Will an extension add value to my property in Kent?
A well-designed and well-built extension typically returns £1.20–£1.50 for every £1 invested at current South East property values. The improvement to your lifestyle is immediate; you realise the financial return when you sell. 

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Do I need a party wall agreement?
If your extension is close to or on a shared boundary with a neighbour, you'll likely need to serve a party wall notice under the Party Wall Act 1996. Our full party wall agreement guide explains the process in straightforward terms.

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Thinking about an extension?

If you're in the early stages of exploring what's possible for your home and budget, we'd welcome an honest conversation.

At Reeve Renovations, we've been delivering design-led extensions across Sevenoaks, Tonbridge, Tunbridge Wells and the wider Kent area since 2010. Every project is overseen personally by Lawrence, with clear communication and transparent pricing throughout.

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There are no surprises, no hidden extras, and no pressure. Just an experienced team who care about getting it right.

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Get in touch to arrange a free quote

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