The short answer
The ideas that improve a kitchen extension most are often the cheap ones: a rooflight where the old house meets the new, a window seat, a pantry wall. The expensive ones are nearly all glass. Decide early which of each you want, because the time to choose is before the drawings are priced.
Most collections of kitchen extension ideas are picture galleries. This one is a price list of sorts. Each idea is marked by what it does to the budget, so you can pick the ones that matter to you and know what you are trading.
Ideas that save money
1. Keep the kitchen in the middle, put the table by the garden
The instinct is to put the new kitchen in the new room. The cheaper and often better plan leaves the units roughly where they are, near the existing drains, boiler and gas, and gives the bright end of the room to the table. You sit in the daylight and cook in the part that needed it least.
2. One large fixed window in place of a wall of doors
Bifold and sliding doors are sold on the idea of opening the whole back of the house. In practice they are fully open for a few weeks a year. A single door to the garden beside a big fixed pane gives the same view for much less, and it leaves wall space for a bench or a radiator.
3. A flat roof you cannot see
A warm flat roof with a parapet hides everything behind a clean line of brick. It costs less than a pitched roof and keeps under the height limits for permitted development.
Ideas that cost little
4. A rooflight over the join
Put a long rooflight where the extension meets the old back wall. It lights the darkest part of the plan, the middle of the house, and washes the old brickwork if you leave it exposed. One well-placed rooflight does more than three scattered ones.
5. A window seat
A deep window at seat height, set into the garden wall, adds a place to sit without taking floor from the room. Built in blockwork with a timber top it costs little more than the window.
6. A pantry wall
Give one windowless wall to full-height cupboards with a shallow walk-in pantry behind sliding doors. It takes storage out of the main run, so the kitchen itself can be smaller and plainer.
7. Exposed structure
If the steel beam over the opening has to be there, consider leaving it visible and painting it. It needs an intumescent coating for fire protection where it would otherwise be boxed in, so mention it to the engineer early.
Ideas that add real money
8. Slim-frame sliding doors
Three-metre panes on frames a couple of centimetres wide look superb and are the largest single upgrade most people make. They need a stiffer beam above so the track stays true, and they have long lead times.
9. A glazed roof or glass box
A fully glazed side return or a frameless glass link is beautiful and unforgiving. It runs up against the building regulations limit on glazing, which is roughly a quarter of the floor area plus the openings you cover up, so the designer has to prove by calculation that the room still holds its heat. Budget for solar-control glass and blinds as well.
10. Cladding that contrasts with the house
Zinc, charred larch or dark brick against a red-brick semi can look very good. Know that permitted development requires materials of similar appearance to the existing house. A contrasting finish usually means a planning application, with its fee and its eight weeks, on top of the cost of the cladding itself.
11. An island with the hob on it
A hob on an island needs an extractor above or beside it that is ducted to outside, because building regulations do not accept a recirculating hood as the kitchen’s extract. That duct has to cross the ceiling to an outside wall. It is simple if planned and awkward if not. Putting the sink on the island and the hob on the wall is cheaper and keeps the cook facing the room.
How to choose
Take one idea from the last group, the one you would miss most, and pay for it properly. Fill the rest of the room from the first two groups. An extension with a single generous move and good plain everything else looks better, and ages better, than one with five half-funded features.
Then put numbers on it. The calculator on our kitchen extension cost guide has three finish levels, and the gap between standard and high for the same floor area is, more or less, the price of everything in that third group.