Garden room kitchen extension: layout, light and cost
A garden room kitchen extension puts the cooking, the table and the garden in one bright room. Most are 20 to 30 m². The building itself costs £45,000 to £75,000 with VAT at 25 m²; the kitchen units, worktops and appliances are bought separately and sit on top of that.
Get a quoteIt suits you if
- The kitchen is at the back of the house and too narrow for a table.
- You want to watch children or the dog in the garden while you cook.
- A conservatory was added off the kitchen years ago and nobody eats in it.
- You are replacing the kitchen anyway, so the disruption happens once.
- The back of the house faces anywhere but due north. North-facing rooms work too, with more roof glass.
What the building costs
| Garden room kitchen extension, building only | Guide price with VAT |
|---|---|
| 20 m² (5 m by 4 m) | £36,000 to £60,000 |
| 25 m² (6 m by 4.2 m) | £45,000 to £75,000 |
| 30 m² (6 m by 5 m) | £54,000 to £90,000 |
| Architect or architectural designer, planning drawings | £1,000 to £2,500 |
| Structural engineer | £600 to £1,200 |
| Householder planning fee in England, if you need to apply | £548 |
Kitchen units, worktops, appliances and their fitting are not included. National prices. A guide, not a quote. Use the cost calculator for your own size.
Put the kitchen at the back and the table at the glass
The instinct is to put the new kitchen in the new room. Usually the better plan is the reverse. Keep the working kitchen in the deeper, darker part of the plan, near the existing drains and the boiler, and give the bright end to the table and a sofa. Cupboards along a glass wall block the view you are paying for, and low sun across a worktop makes chopping and reading a screen harder than you would expect.
An island or peninsula on the line where old house meets new room works well. The cook faces the garden, and the steel beam overhead has a reason to be there.
How much glass you are allowed
Building regulations cap the glazing in an extension. As a starting point, windows, doors and roof lights together may equal 25% of the new floor area, plus the area of any windows and doors that the extension covers up. A 25 m² room that swallows a 4 m² patio door therefore starts with about 10 m² of glass, which is roughly a 4 m sliding door and one roof light.
You can go beyond that. The designer has to show by calculation that the room loses no more heat than a version built to the standard figures would, which in practice means better glass, thicker insulation elsewhere, or both. It is routine for glazed kitchen extensions; it is also why triple glazing and well-insulated roofs appear on these quotes.
Steam, smells and the cooker hood
One open room means the kitchen has to clear its own air. The ventilation rules ask for an extractor that moves 30 litres a second if it sits over the hob, or 60 litres a second if it is elsewhere in the room, ducted to outside. A recirculating hood does not count. Decide the duct route before the ceiling is closed; through a flat roof is simple, across a long ceiling to a side wall is not.
Drains decide more than you think
Moving the sink more than a couple of metres means a new waste run under the new floor. Find out early where the existing drains and any manhole are. If a public sewer runs within 3 m of the new foundations you will need a build-over agreement from the water company, and a manhole inside the footprint has to be moved or sealed with a double cover. None of this stops a project. All of it is cheaper to know in week one than in week six.
Living through the build
A well-run job builds the new shell first and leaves the back wall of the house alone until the room is weathertight. The old kitchen keeps working through most of the build. The hard stretch comes at the end: once the wall comes out and the new kitchen goes in, plan for two to four weeks without one. A microwave, a kettle and a washing-up bowl in the dining room are the usual answer.
In Scotland the same job needs a building warrant before work starts, so allow for that in the timetable.
Get the building priced before you choose the kitchen.
Get a quoteHow a kitchen extension runs
Design, with the kitchen in it
The room and the kitchen layout are drawn together, so drains, ducts and sockets land in the right place.
Engineer and approvals
Beam calculations, building control, a build-over agreement if a sewer is close.
Shell first
Typically ten to fourteen weeks for footings, walls, roof and glazing while the old kitchen stays in use.
Knock through and fit
The wall comes out, floors are levelled, then first-fix services, plaster and the new kitchen.
Garden room kitchen extension questions
Can you put a kitchen in a garden room extension?
Yes. Because it is built to full building regulations and heated from the house, it is an ordinary room and can hold a kitchen. A conservatory is a poor place for one: it is too hot, too cold and too humid by turns.
How big should a garden room kitchen extension be?
For a kitchen, a table for six and a way through to the garden, 20 to 25 m² added to the existing kitchen is comfortable. Under 15 m² you are adding a dining end to the kitchen you have, which can be all it needs.
Will a glazed kitchen extension overheat?
It can if every surface is glass. A solid roof with one or two opening roof lights, solar-control glass to the south and west, and doors that open wide keep it comfortable. Cooking adds heat too, so the extractor matters.
Do I need planning permission?
Not usually, if the room stays within the permitted development limits for a single-storey rear extension. A flue or extract on a wall facing the road, or a house in a conservation area, can change that.
Is underfloor heating worth it?
In a room with glass where the radiators would go, yes. A wet system in the new floor slab runs off the boiler or a heat pump, frees the walls and takes the chill off a tiled floor. It needs deciding before the floor is poured.
How long will I be without a kitchen?
Two to four weeks on a job that is sequenced well, at the end of the build. Ask each builder how they plan that stretch and judge them partly on the answer.
Sources
- Approved Document L: conservation of fuel and power (GOV.UK)
- Approved Document F: ventilation (GOV.UK)
- Permitted development rights for householders: technical guidance (GOV.UK)
- Building regulations approval (GOV.UK)
- Building warrants (mygov.scot)
- Single-storey extension costs (Federation of Master Builders)
Get a quote for a garden room kitchen extension
Postcode first, then four quick questions about the room, then your contact details. It takes about a minute and costs nothing.
We are not a builder. We look for a firm that builds this kind of room near you and tell you its name. Nothing is passed on until you say so.
Got it, thank you.
- We look for a firm that builds glazed extensions around your postcode, then email or phone you with its name.
- If you are happy with that firm, we send your enquiry across. If not, it goes nowhere.
- The firm measures up at the house and gives you its price. You will not hear from us about anything else.