Single-Storey Extension Costs in Kent: 2026 Complete Price Guide

Overview

Single Storey Extensions

Single-Storey Extension Costs in Kent: 2026 Prices

A single-storey rear extension is the most cost-effective way to add real living space to a Kent home — typically a kitchen-diner, family room, or open-plan living area.

Average Cost by Size

3m x 3m (9 m²) — £28,000–£42,000. Compact kitchen extension.

3m x 5m (15 m²) — £38,000–£58,000. Standard kitchen-diner.

4m x 6m (24 m²) — £52,000–£78,000. Open-plan family extension.

5m x 7m (35 m²) — £70,000–£105,000+. Large family living space.

These are finished prices including kitchen fit-out, flooring, decoration, and bi-fold doors to a mid-range spec.

What's Included

Architectural drawings and structural calculations

Planning application (or prior notification under PD)

Building Regulations submission and inspections

Foundations (typically trench fill, deeper on Kent clay)

Cavity wall construction (brick or render finish)

Warm flat roof or pitched roof with rooflights

Bi-fold or sliding doors (typically £4,000–£10,000)

Electrics, plumbing, heating extension

Plastering and decoration

Flooring

Kitchen fit-out (if extending the kitchen)

Building control sign-off

What Affects the Final Cost

Foundations — Kent clay often needs 1.5–2m deep foundations (+£3,000–£8,000)

Glazing spec — bi-folds vs sliders vs French doors makes £5,000+ difference

Roof type — flat warm roof is cheapest; pitched with vaulted ceiling adds £5,000–£12,000

Kitchen spec — £8k budget vs £25k high-end

Steel beams — knocking through to existing house adds £2,000–£5,000

Drainage diversion — if foul/surface water runs under the extension footprint

Party Wall Agreements — common on terraces and semis (£800–£2,000)

Permitted Development vs Planning

Most single-storey rear extensions in Kent are built under permitted development:

Up to 4m deep for detached, 3m for semi/terrace (standard PD)

Up to 8m deep for detached, 6m for semi/terrace (Larger Home Extension prior notification)

Maximum 4m height (3m within 2m of boundary)

Materials must match existing

Conservation areas and listed buildings have tighter rules.

Build Time

Typical Kent single-storey extension: 10–14 weeks from groundworks to sign-off.

Related Guides

Home Extension Cost Reigate

Kitchen Extension Guide Kent

Loft Conversion or Extension?

Call 07850 357962 or request a free Kent extension quote.