Kitchen Extensions UK: Costs, Design and Planning Guide 2025

A well-planned kitchen extension can transform daily life—more space, better light and flow, and a sociable hub for family and friends. This guide covers the benefits and types of kitchen extensions, when you need planning permission, the building regulations that apply, realistic 2025 costs, key design decisions, common pitfalls—and how Fixiz delivers compliant projects on time and on budget.

Benefits of a Kitchen Extension

Space and flow: Create an open-plan kitchen-diner with room for island seating and storage.
Light and garden connection: Add sliders/rooflights for daylight and inside-out living.
Everyday practicality: Integrate utility, pantry and improved circulation.
Value uplift: Quality extensions can boost saleability in space-constrained areas.

Types of Kitchen Extensions

Rear Extension

What it is: Build out to the garden to enlarge the kitchen-diner.
Why choose it: Most straightforward layout; often eligible for permitted development (PD) if limits are met. [Planning Portal] :contentReference[oaicite:0]{index=0}

Side Return

What it is: Infill the narrow side passage typical of Victorian/Edwardian terraces.
Why choose it: Big impact on kitchen width and natural light; tighter sites mean higher £/m².

Wrap-Around (Rear + Side)

What it is: Combines rear and side return for maximum re-planning of the ground floor.
Why choose it: Best for dramatic open-plan “family room” layouts; more complex structure and planning.

Planning Permission Requirements

Permitted Development: Many single-storey rear additions qualify as PD where strict size/height/placement limits are met. If limits are exceeded, apply for householder planning. [Planning Portal] :contentReference[oaicite:1]{index=1}
Kitchen-specific FAQs: A rear kitchen extension can be PD; external alterations (e.g., big roof changes) may require consent. [Planning Portal FAQ] :contentReference[oaicite:2]{index=2}
Designated land & Article 4: Conservation areas/Article 4 Directions can restrict PD—check early. [PD rights overview] :contentReference[oaicite:3]{index=3}

Building Regulations for Kitchen Extensions

Structure (Part A): Foundations, stability and correctly sized beams/lintels over wide openings.
Energy (Part L): Compliant U-values, airtightness and thermal bridge control for walls/roof/floor and high-performance glazing.
Ventilation (Part F): Kitchens require effective extract to outside; design airflow rates per Approved Document F. [Gov.UK Part F] :contentReference[oaicite:4]{index=4} [ADF Vol.1] :contentReference[oaicite:5]{index=5}
Safety (Part K/B): Stairs/guarding where levels change; fire separation/alarms as needed.
Drainage & moisture (Parts H/C): Foul/waste layouts, build-over consents, damp proofing.

Typical Costs in 2025

Per m² benchmarks (build only): Single-storey kitchen extensions commonly £1,800–£3,500/m²; double-storey often £1,650–£3,250/m². Side returns tend to sit toward the upper end due to access/complexity. [Livingetc 2025] :contentReference[oaicite:6]{index=6}
Kitchen-led examples: A 30 m² single-storey kitchen extension might total £66,000–£99,000 + VAT (build). [Homebuilding & Renovating 2025] :contentReference[oaicite:7]{index=7}
General extension ranges: House extensions frequently price at ~£1,800–£3,000/m² with typical 20–50 m² projects scaling accordingly. [Checkatrade] :contentReference[oaicite:8]{index=8}
Kitchen fit-out (separate from build): Mid-range kitchen supply & fit often £12,000–£25,000 depending on cabinetry, worktops and appliances. [Beams 2025] :contentReference[oaicite:9]{index=9}
Fees & contingency: Allow 10–15% for professional/statutory fees and at least 10% contingency. [Livingetc 2025] :contentReference[oaicite:10]{index=10}

Design Considerations

Layout & Workflow

Plan from the inside out: Fix zones (prep/cook/clean/store) before choosing doors or rooflights.
Island vs peninsula: Maintain circulation (ideally ≥1000 mm clear routes) and ergonomic work triangles.

Light, Glazing & Overheating

Balanced daylight: Mix vertical glazing with rooflights; consider shading/low-g glazing to manage summer gains.

Utilities & Services

Ventilation: Duct cooker hoods externally; size extract per Part F (boost rates and background ventilation). [ADF Vol.1] :contentReference[oaicite:11]{index=11}
Electrics & lighting: Layer task, ambient and accent lighting; ensure circuit capacity and RCD protection.
Plumbing & drainage: Plan waste runs early—especially for islands and utility sinks.
Heating & energy: Consider underfloor heating and upgraded insulation to meet Part L targets.

Common Mistakes—and How to Avoid Them

Designing shell before layout: Leads to awkward kitchens. Fix: Freeze layout and appliance plan first.
Underestimating structure: Wide openings without early engineering = cost/time creep. Fix: Get structural calcs pre-tender.
Assuming PD without checks: Designated land/Article 4 can remove rights. Fix: Confirm PD status early. [PD rights] :contentReference[oaicite:12]{index=12}
Ignoring ventilation: Recirculating hoods only can fail compliance. Fix: Provide ducted extract per Approved Document F. :contentReference[oaicite:13]{index=13}
Optimistic budgets: Forgetting VAT/fees/contingency. Fix: Add fees 10–15% and ≥10% contingency. :contentReference[oaicite:14]{index=14}

How Fixiz Delivers Kitchen Extension Projects

Feasibility first: We confirm PD vs planning, map constraints (drain runs, party wall, access) and set realistic budgets/programmes. :contentReference[oaicite:15]{index=15}
Design you can build: Architect-led layouts coordinated with structure and services, so openings, steels and drainage work on site.
Approvals handled: Full Plans with Building Control; ventilation and energy details aligned to Parts F and L for smooth sign-off. :contentReference[oaicite:16]{index=16}
Transparent pricing: Itemised proposals tied to current 2025 £/m² benchmarks and a separate kitchen fit-out allowance to avoid surprises. :contentReference[oaicite:17]{index=17}
Programme discipline: We sequence long-lead items (windows, kitchens) against approvals to keep the build moving.

Conclusion

The best kitchen extensions start with a clear brief, robust planning checks, engineered structure, and compliant ventilation/energy details—plus a budget that reflects 2025 realities. With Fixiz coordinating design, permissions, building control and delivery, you get a bright, practical space and a smooth journey from brief to breakfast bar.

Ready to plan your kitchen extension?

Speak to Fixiz today for feasibility checks, design, approvals and itemised pricing—so your kitchen extension is done right, first time.

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