An open plan kitchen extension can genuinely transform a home when it is planned around how a family actually moves, cooks and relaxes, not just how it looks in a photo. Budget realistically for roughly £2,400 to £3,400 per square metre outside London, check whether your project falls under permitted development, and confirm ventilation and structural requirements before you commit to a design.
TL;DR:
- Outside Greater London, single storey extensions typically cost £2,400 to £3,400 per square metre; London rates rise to £3,200 to £4,400.
- Budget about £82,500 for a 30 square metre mid range extension, then add 25% to 30% for fees and VAT and at least 10% contingency.
- Choose an island only if it leaves at least 1,200mm of clearance on every side; narrower extensions often suit a peninsula or galley layout.
- Standard permitted development covers rear extensions up to 4m for detached homes and 3m for others; conservation areas and listed buildings usually need planning consent.
- The shell build commonly takes 12 to 16 weeks; confirm drainage routes, structural openings, and kitchen dimensions early to avoid costly changes during construction.
Table of Contents
- Practical open plan layout options and glazing choices
- How much an open plan kitchen extension costs and how to budget
- When you need planning permission and what permitted development allows
- Regulatory must-haves: ventilation, fire protection and structural work
- A realistic project timetable and staged process from brief to handover
- Operational design tips: acoustics, storage, lighting and extraction
- How Extension Kings' managed design-and-build approach helps homeowners
- Working with your contractor without the disruption taking over
- Prioritise function over design flourishes
- Ready to plan your own kitchen extension?
- FAQ
- Sources
Practical open plan layout options and glazing choices
The right layout depends on how your household lives, not on what looks striking in a showroom. An island works well when you have at least 1,200mm of clearance on every side, giving you a social cooking zone without blocking the route to the garden doors. A peninsula suits narrower plots or side return extensions where a freestanding island would eat into circulation space. Galley-style runs still make sense in longer, narrower extensions where storage matters more than a central gathering point.
Think in zones rather than one undivided room: a cooking zone close to plumbing and extraction, a dining zone near the garden view, a soft seating pocket, and a utility or pantry area tucked out of sight for noisy appliances and overflow storage.
Glazing choices shape how the space feels and functions:
- Full-width bifold or sliding doors blur the line between kitchen and garden but can limit usable wall space for cabinetry.
- Rooflights bring daylight into the centre of a deep extension without sacrificing wall storage.
- Side windows maintain privacy from neighbours while still lighting a prep area.
Before committing, test the layout on paper or with simple tape marks on the existing floor, checking furniture footprints, walking routes and appliance door swings.
Pro Tip: Mark out your proposed island or peninsula with masking tape on the current floor and walk your usual cooking routine through it before finalising the design.
How much an open plan kitchen extension costs and how to budget
Build costs for single-storey extensions outside Greater London commonly sit between £2,400 and £3,400 per square metre, with London rates running higher at around £3,200 to £4,400 per square metre.
A mid-range 30 square metre kitchen extension can be budgeted around £82,500 excluding VAT, giving you a usable starting point before a surveyor or contractor quotes your specific site.
When building your budget, allow for:
- The shell: foundations, structural steel, brickwork and roof.
- Fit-out: kitchen units, worktops, flooring and decoration.
- Professional fees and VAT, which commonly add another 25 to 30% on top of the base build cost.
- A contingency fund of at least 10% for unforeseen issues once walls or floors are opened up.
Watch for provisional sums or prime cost allowances in builder quotes. These are placeholders for items like kitchen fittings that have not yet been chosen, and unless they are clearly defined in writing they are a frequent source of budget overruns. Ask for itemised, fixed-price allowances wherever possible, and agree staged payments tied to completed work rather than calendar dates.
When you need planning permission and what permitted development allows
Many single-storey rear and side extensions can proceed under permitted development rather than a full planning application, but the limits are specific.
- Standard permitted development limits allow single-storey rear extensions up to 4m for detached houses or 3m for other house types without needing full planning consent.
- Larger single-storey extensions can reach up to 8m (detached) or 6m (other house types) through the prior approval route, which involves notifying neighbours via the local council.
- Designated land exceptions apply: permitted development rights are restricted or removed entirely in conservation areas and for listed buildings, so these projects usually need a full householder planning application.
- Check before you design: use the Planning Portal's interactive guidance, speak to your local planning officer, and have scaled drawings prepared so any query can be answered quickly.
Even where permitted development applies, Building Regulations approval is still normally required, and you remain responsible for obtaining Final Certificates from Building Control, which matter later for conveyancing.
Regulatory must-haves: ventilation, fire protection and structural work
Building regulations shape far more of an open plan kitchen than most homeowners expect. Building-regulations guidance requires both purge and background ventilation for new kitchens, meaning opening windows sized to the floor area plus permanent trickle vents, and mechanical extract ventilation is required to control humidity and cooking odours.
Most extensions require Building Regulations approval even when planning permission itself is not needed, covering doors and windows, drainage, electrics, external walls and internal finishes.
Key points to plan around:
- Inserting a structural beam to create a large kitchen opening normally needs fire protection, such as fire-resistant boarding, around the exposed steel.
- Drainage, electrics and structural changes typically trigger a building-control inspection at key stages.
- A structural engineer is essential whenever you remove a load-bearing wall, calculating beam sizes and specifying padstones correctly.
- Ventilation strategy should be agreed at design stage, not retrofitted once the kitchen layout is fixed.
A realistic project timetable and staged process from brief to handover
Open plan kitchen extensions typically move through four broad stages, though durations vary with scale and planning route.
- Initial consultation and feasibility: establishing layout options, rough budget and whether planning permission or permitted development applies.
- Design and approvals: finalising drawings, structural calculations and any planning or prior-approval submission, generally taking several weeks before site work can start.
- Shell build: foundations, structure and roof, commonly running 12 to 16 weeks for a typical single-storey kitchen extension.
- Fit-out and snagging: kitchen installation, flooring, decoration and final checks before handover.
Lock in drainage routes, structural opening positions and the kitchen footprint as early as possible, since changing any of these mid-build causes expensive rework. Plan a temporary kitchen arrangement, even a simple kettle and microwave setup in another room, to reduce disruption while the main space is unusable.
Operational design tips: acoustics, storage, lighting and extraction
Open plan living amplifies noise, so soft furnishings, rugs and partial screens between the kitchen and seating area help absorb sound that would otherwise bounce off hard floors and glazing. Zoned ceiling treatments, such as a dropped bulkhead over the kitchen run, can also help contain cooking noise and cooking smells to one part of the room.
Storage needs careful thought once wall space is shared between cooking, dining and living functions:
- Larder or pantry pockets keep bulky items out of sight without eating into visible wall runs.
- Integrated appliances and pull-out or down-draw storage make the most of tighter floor plans.
- A separate utility room gives you somewhere to hide washing machines, tumble dryers and extractor noise away from the main living space.
Lighting works best in layers: ambient ceiling light for general use, task lighting over the island and prep zones, and accent lighting for the dining area. For practical guidance on planning these layers before your electrician first fix, see this kitchen lighting plan guide.
Pro Tip: Choose your extractor fan's extraction rate based on your hob's output, not room size alone, since undersized extraction is one of the most common complaints in finished open plan kitchens.
How Extension Kings' managed design-and-build approach helps homeowners
Our approach is to coordinate design, planning, building regulations and construction as a single process, so you deal with one accountable team rather than juggling separate architects, planners and builders. We aim to set realistic budgets early and keep communication clear throughout. This managed approach suits homeowners who want predictable costs and one point of contact for various types of extensions such as kitchen, single-storey, wrap-around and over-garage additions.
Working with your contractor without the disruption taking over
A good working relationship with your contractor starts before the first spade goes in the ground. Agree a written schedule of works, a payment plan tied to milestones, and a clear process for approving any variation to the original specification. Verbal changes agreed on site are the most common cause of disputes over final cost.
Keep a single point of contact on the build, whether that is a project manager or the lead contractor, rather than fielding separate questions from different trades. Weekly check-ins, even brief ones, catch small issues before they become costly delays.
Expect genuine disruption: dust, noise and restricted access to parts of your home for several weeks at a time. Protect flooring and furniture in adjoining rooms before work starts, and agree working hours with your contractor in advance, particularly if you have close neighbours affected by noise or site access.
If the works affect a shared wall, building over or astride a boundary, or excavations near a neighbour's foundations, Party Wall Act notice requirements apply and sometimes require detailed drawings to be shared with the adjoining owner. Sorting this early avoids delays once the build is under way.
Finally, agree a snagging process in writing before handover: a list of minor defects, a timeframe for fixing them, and a final retention payment released only once they are resolved.
Prioritise function over design flourishes
Get circulation, storage and ventilation right first. Glazing and finishes matter, but they only pay off once the basics work. Sketch your brief and arrange a site survey before choosing anything decorative.
— Raja
Ready to plan your own kitchen extension?
We offer design and build services for kitchen extensions, single-storey additions and wrap-around extensions, managing planning, building regulations and construction as one team.
If you want a realistic starting figure for your project, our West Midlands extension cost guide breaks down typical pricing by extension type. Get in touch through Extension Kings to arrange a site survey and discuss your brief.
FAQ
Do you need planning permission for a kitchen extension?
Many single-storey kitchen extensions can proceed under permitted development if they stay within standard dimensional limits, but larger extensions or those on designated land such as conservation areas usually need a full planning application. Building Regulations approval is still required even when planning permission is not.
What is the average cost of a kitchen extension?
Build costs for single-storey extensions typically range from £2,400 to £3,400 per square metre outside Greater London, with London rates running higher. A mid-range 30 square metre extension can be budgeted around £82,500 excluding VAT, professional fees and finishes.
What are some decorating ideas for an open plan kitchen diner?
Soft furnishings, rugs and layered lighting help an open plan kitchen diner feel warm rather than clinical, while a cohesive colour palette ties the cooking and seating zones together visually. For finish and soft furnishing ideas that also help manage noise near a kitchen diner, this living room decorating guide offers practical direction.
How do I close off part of an open plan kitchen?
Partial screens, sliding doors or a half-height partition let you separate a kitchen from a living area when needed without fully reverting to a closed-plan layout. Dropped ceiling bulkheads or a change in flooring material can also visually divide zones while keeping the overall space open.