Kitchen Extension: Planning, Costs and Design Ideas
Everything you need to know about planning a kitchen extension, from permitted development rules and costs to layout ideas and choosing an architect.
A kitchen extension is one of the most popular and valuable home improvement projects in the UK. Whether you want a bright, open-plan kitchen-diner, a family living space that opens onto the garden, or simply more room to cook and entertain, extending your kitchen can transform how you use your home.
Do You Need Planning Permission?
Many kitchen extensions can be built under permitted development rights without planning permission. The key limits for a single storey rear extension are:
- Detached houses: up to 4 metres beyond the original rear wall (or up to 8 metres with prior approval under the larger home extension scheme)
- Semi-detached and terraced houses: up to 3 metres (or up to 6 metres with prior approval)
- Maximum height: 4 metres (or matching the existing eaves height, whichever is lower)
- Maximum eaves height: 3 metres if within 2 metres of a boundary
If your extension is within these limits and meets all other PD conditions, you do not need planning permission. However, you may still want to apply for a Lawful Development Certificate to confirm compliance - particularly useful when selling your home.
You will need planning permission if:
- The extension exceeds PD size limits
- Your property is in a conservation area (where the larger extension scheme does not apply)
- Your home is a listed building
- An Article 4 Direction applies
- Your home is a flat or maisonette
How Much Does a Kitchen Extension Cost?
Kitchen extension costs in the UK vary widely depending on size, specification, and location. As a rough guide:
| Extension Size | Build Cost (exc. kitchen) | Total Budget (inc. kitchen fitout) |
|---|---|---|
| Small (10-15m²) | £25,000 – £45,000 | £40,000 – £65,000 |
| Medium (15-25m²) | £40,000 – £70,000 | £60,000 – £100,000 |
| Large (25-40m²) | £65,000 – £110,000 | £90,000 – £150,000 |
Costs are higher in London and the South East, typically 15–25% above national averages. For a detailed breakdown, read our guide to house extension costs.
Major cost factors include:
- Structural work - steel beams to create open-plan spaces can cost £2,000–£5,000+ each
- Roof type - flat roofs are cheaper than pitched roofs; roof lanterns add £3,000–£8,000
- Glazing - bi-fold or sliding doors to the garden typically cost £3,000–£10,000
- Underfloor heating - £50–£100 per square metre installed
- Kitchen units and appliances - from £5,000 for budget to £30,000+ for premium
Design Ideas and Layout Options
Open-Plan Kitchen-Diner
The most popular layout is an open-plan kitchen, dining, and living area. This creates a single, sociable space that is ideal for families. Key design considerations include:
- Positioning the cooking area with a view of the dining and living zones
- Including a kitchen island for prep, casual dining, and as a visual divider
- Placing bi-fold or sliding doors along the rear wall to connect with the garden
- Using consistent flooring throughout to create a sense of flow
Side Return Extension
For Victorian and Edwardian terraced houses, extending into the narrow side return (the alley between your house and the boundary) is an efficient way to gain space. Side return extensions typically add 2–3 metres of width to the kitchen, transforming a narrow galley kitchen into a spacious room. Most side return extensions fall within permitted development limits.
Wraparound Extension
A wraparound extends both to the rear and into the side return, creating an L-shaped addition. This maximises floor area and is particularly effective for corner plots or detached houses. Wraparound extensions often require planning permission as they combine side and rear elements.
Roof Lanterns and Skylights
Natural light is critical in a kitchen extension. Options include:
- Roof lanterns - a raised glass box on a flat roof, flooding the centre of the room with light
- Skylights - individual rooflights positioned over key areas (worktops, island)
- Glazed roof sections - larger areas of structural glazing for a dramatic effect
The Process: From Concept to Completion
- Feasibility and budget - decide what you want to achieve and set a realistic budget
- Appoint an architect - an architect will design the extension, prepare drawings, and manage the planning process
- Planning permission or PD confirmation - either submit a planning application or apply for a Lawful Development Certificate
- Building regulations application - submit detailed technical drawings for building control approval
- Structural engineer - commission structural calculations for foundations, steelwork, and any load-bearing changes
- Appoint a builder - get at least three quotes and check references. Find a contractor near you
- Construction - typically 8–16 weeks for a single storey kitchen extension
- Kitchen installation - usually by a specialist kitchen fitter, 1–3 weeks
- Building control sign-off - obtain a completion certificate
Building Regulations
Regardless of whether planning permission is needed, a kitchen extension must comply with building regulations covering:
- Foundations - depth and type depend on ground conditions (typically 1m+ deep)
- Structure - walls, floors, and roof must meet structural standards
- Insulation - walls, floor and roof must meet current U-value requirements
- Drainage - connection to the existing drainage system
- Ventilation - extractors and trickle vents as required
- Electrics - must be done or certified by a Part P registered electrician
How Much Value Does a Kitchen Extension Add?
A well-designed kitchen extension typically adds 5–10% to the value of your home - and potentially more if it creates an open-plan living space or adds a bedroom (through a two storey extension). In many areas, the value added exceeds the cost of the extension, making it one of the best returns on investment in home improvement.
A kitchen extension is a significant project, but with the right design and team it can be straightforward and hugely rewarding. Start with a clear brief, find a good architect, and plan your budget carefully - the result will transform your daily life at home.