House Extension Costs in Kent: 2026 Complete Price Guide

House Extension Costs in Kent: What to Budget in 2026

The type of extension moves the budget more than anything else — our pages on single storey extensions and kitchen extensions cover the two most common projects in detail.

A house extension is one of the most significant — and rewarding — investments you can make in your Kent property. Whether you need more kitchen space, an extra bedroom, or a larger living area, an extension adds both usable space and substantial property value. But how much should you budget?

This guide gives you transparent, realistic pricing for house extensions across Kent, based on our experience building extensions in Tunbridge Wells, Sevenoaks, Tonbridge, Maidstone, and throughout the county.

Average House Extension Costs in Kent

Single-Storey Rear Extension (£30,000 – £55,000)

The most popular extension type, typically creating a new kitchen-diner or enlarged living space.

Typically includes:

Size guide: A typical single-storey rear extension in Kent is 3m–6m deep by the full width of the property (usually 4m–6m). That's 12–36 sqm of additional floor space.

Cost per sqm: £1,200–£2,000 depending on specification.

Double-Storey Extension (£50,000 – £90,000)

Maximises space by adding rooms on two levels — typically a kitchen-diner below and bedroom/bathroom above. See our double storey extensions page for how the two-level build runs.

Typically includes:

Cost per sqm: £1,000–£1,600 (better value than single-storey due to shared foundations and roof).

Side-Return Extension (£20,000 – £40,000)

Opens up narrow Victorian and Edwardian terraces by building into the side alley.

Typically includes:

Best for: Terraced and semi-detached homes in towns like Tunbridge Wells, Tonbridge, and Bromley.

Wraparound Extension (£45,000 – £75,000)

Combines rear and side-return extensions for maximum space. Our wrap-around extensions page covers how these L-shaped builds are planned and quoted.

Typically includes:

What Affects the Cost?

1. Size and Complexity

Larger extensions cost more, but the cost-per-sqm typically decreases as size increases. Complex shapes (L-shaped, wraparound) cost more than simple rectangles.

2. Foundations

Kent has varied soil conditions — from clay in the Weald to chalk on the North Downs. Clay soils often require deeper foundations (up to 1.5m), which increases costs by £3,000–£8,000.

3. Specification

A basic extension with standard finishes differs significantly from one with underfloor heating, bi-fold doors, skylights, and a bespoke kitchen. High-spec finishes can add 30–50% to the base build cost.

4. Structural Steel

Most extensions require at least one steel beam (RSJ) to support the existing structure where walls are removed. Steel typically costs £1,500–£4,000 depending on the span.

5. Planning and Professional Fees

Architectural drawings (£1,500–£3,000), structural engineering (£500–£1,500), planning applications (£250+), and Building Regulations fees (£500–£1,000) are additional costs to factor in.

Do You Need Planning Permission?

Many extensions in Kent fall under Permitted Development (PD) rights, meaning no planning application is needed. The key PD limits are:

You WILL need planning permission if:

We assess every property's PD rights during our free site survey and handle all planning applications if needed.

How Long Does a House Extension Take?

| Extension Type | Typical Build Time |

|---|---|

| Side-return | 6–8 weeks |

| Single-storey rear | 8–12 weeks |

| Double-storey | 12–16 weeks |

| Wraparound | 12–16 weeks |

Note: These timelines are for the construction phase only. Allow 4–8 weeks beforehand for design, planning, and Building Regulations approval.

Does an Extension Add Value?

Yes — a well-designed extension typically adds more value than it costs. Industry data suggests:

In Kent, where property prices range from £300,000–£800,000+, this translates to significant returns on your investment.

Our Extension Process

1. Free site survey — We visit your property, discuss your requirements, and assess the site

2. Design and planning — Architectural drawings, structural engineering, and planning applications

3. Detailed quote — Itemised, fixed-price quote with no hidden extras

4. Construction — Foundations, structure, roof, internal fit-out

5. Completion — Building Regulations sign-off, snagging, and handover

Why Choose Mighty Oak for Your Kent Extension?

We're a family-run building company based in Tunbridge Wells with extensive experience building extensions across Kent. We manage the entire project from design to completion, coordinating all trades under one project manager. No subcontractors, no surprises — just quality building work delivered on time and on budget.

Ready to discuss your extension project? Get a free quote or call us on 07850 357962.

House Extension Cost FAQs

How much does a wraparound extension cost in Kent?

A wraparound extension in Kent typically costs £45,000–£75,000. It combines a rear and side-return extension into an L-shaped or U-shaped floor plan, so the price reflects multiple structural openings as well as the larger footprint.

How much does a double storey extension cost in Kent?

A double-storey extension in Kent typically costs £50,000–£90,000, working out at £1,000–£1,600 per square metre. That is better value per metre than a single-storey build, because the foundations and roof are shared across two floors of new space.