How-To Guide · Updated June 2026 · UK Extensions

How to Plan a Kitchen Extension Step by Step in 2026

A kitchen extension is one of the highest-value improvements you can make - but the difference between a smooth build and an expensive headache is in the planning. This 2026 guide takes you through it step by step: checking feasibility and structure, confirming whether you need planning permission, meeting Building Regulations and drainage rules, setting a realistic GBP 40,000 to GBP 80,000 budget, and following a 10 to 16 week build timeline.

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6-step plan
Updated June 2026
GBP 40k-80k budget
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Step by Step · 2026

The 6 Steps to Planning a Kitchen Extension

1. Assess space and feasibility

Decide on a rear, side or wraparound layout. A usable family kitchen-diner needs about 18 to 30 square metres. Check where doors, windows and the existing kitchen services sit, and how the new space connects to the rest of the house.

2. Confirm the planning route

Many single-storey rear kitchen extensions are Permitted Development within the depth, height and coverage limits, or use the Larger Home Extension prior-approval route up to 6m or 8m. Conservation areas, listed buildings and two-storey or wraparound schemes need full planning.

3. Design the layout, structure and drainage

Position the run of units and island around the cooking triangle, plan glazing for light (rooflights, bi-folds or a lantern), and confirm the steel beam for any knock-through. Locate the soil and waste connections early, and arrange a build-over agreement if you build near a public sewer.

4. Submit Building Regulations

Lodge a Full Plans or Building Notice application (GBP 500 to GBP 1,000). Building Control inspects foundations, structure, thermal performance, drainage, ventilation, electrics and glazing. Serve any party wall notices at least 2 months before work starts.

5. Set the budget and specification

Allow GBP 2,000 to GBP 3,000 per square metre for the shell, plus GBP 8,000 to GBP 25,000 for the kitchen itself depending on units and appliances. Lock down glazing, flooring, heating and lighting up front to avoid mid-build changes.

6. Get 3 quotes and build

Use BestBuilders to compare 3 free quotes from vetted UK extension builders against the same brief. Check each includes drainage, Building Control liaison, the kitchen fit scope and a completion certificate.

Budget & Timeline

Kitchen Extension Cost and Timeline

SizeTypical 2026 costBuild time
Small (12-18 m²)GBP 30,000-45,0008-12 weeks
Medium (18-25 m²)GBP 45,000-65,00010-14 weeks
Large (25-35 m²)GBP 60,000-85,00012-16 weeks

London and the South East add roughly 15 to 25 percent. A roof lantern, bi-fold doors or underfloor heating push you toward the top of each range.

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FAQ · 2026

How to Plan a Kitchen Extension FAQs · 2026

Start by assessing feasibility and the size you need - a family kitchen-diner usually wants 18 to 30 square metres. Then confirm whether the scheme is Permitted Development or needs planning, design the layout, structure and drainage, lodge Building Regulations, set a GBP 40,000 to GBP 80,000 budget, and get three like-for-like quotes before committing.
Often no. Many single-storey rear kitchen extensions are Permitted Development if they stay within the depth, height and coverage limits, or use the Larger Home Extension prior-approval route up to 6m on a terrace or semi and 8m on a detached house. Full planning is needed in conservation areas, on listed buildings, and for two-storey or wraparound schemes. Building Regulations always apply.
A single-storey kitchen extension typically costs GBP 40,000 to GBP 80,000 in 2026 - roughly GBP 2,000 to GBP 3,000 per square metre for the shell plus GBP 8,000 to GBP 25,000 for the kitchen itself. London and the South East add 15 to 25 percent, and features like a roof lantern, bi-fold doors or underfloor heating push costs toward the top of the range.
Most kitchen extensions take 10 to 16 weeks on site, from foundations through structure, roof, glazing, first and second fix to the final kitchen install. Small extensions can finish in 8 to 12 weeks; larger or more complex builds with structural openings take longer. Allow extra lead time for planning and Building Regs before work starts.
Yes, always, even when the extension is Permitted Development. Building Control checks foundations, structure, thermal performance, drainage, ventilation, electrics and glazing. Expect a fee of GBP 500 to GBP 1,000 and inspections at key stages, with a completion certificate required to sell the property.
Plan the kitchen sink, dishwasher and any utility waste runs to the existing drainage early. If you build within 3m of a public sewer you will usually need a build-over agreement with the water authority. Your builder and Building Control will confirm gradients and connections as part of the application.
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Compare GuideHow to Compare Kitchen Extension Quotes →Planning GuideRear Extension Planning Permission 2026 →