The short answer
Allow 10 to 16 weeks of building for a single-storey kitchen extension. The part people underestimate is everything before the builder arrives: drawings, permission, building regulations and party wall notices usually add four to six months, so seven to ten months from first sketch to finished kitchen is a fair plan.
Before the builder: four to six months
Nothing on site can start until four pieces of paper are in order, and each has a clock that you cannot hurry.
Drawings. A designer needs to measure the house, draw what is there and then draw what you want. For a simple rear extension that takes four to eight weeks, most of it spent waiting for your decisions.
Permission. If the extension is permitted development you do not have to apply for anything, though a lawful development certificate is worth having and the council takes up to eight weeks to issue one. A householder planning application has the same eight-week target. The larger home extension route, for single-storey extensions up to 6 m or 8 m deep, gives the council 42 days.
Building regulations. Every extension needs approval. With a full plans application the council checks the drawings before work starts and must decide within five weeks, or two months if you agree to an extension. The structural engineer’s calculations have to be ready first.
Party wall notices. In England and Wales, if you are building at the boundary or digging near a neighbour’s foundations you must give written notice at least one month before starting, and two months for work to a shared wall. The neighbour has 14 days to reply. Silence counts as a dispute, and then surveyors have to be appointed.
Some of these overlap. Building regulations drawings can be prepared while planning is being decided, and notices can go out as soon as the design is fixed. Run in sequence they take most of a year. Run together, four to six months.
On site: 10 to 16 weeks
The build follows the same order on almost every job.
| Stage | Typical time | What you will see |
|---|---|---|
| Groundworks | 2 to 3 weeks | Digging, concrete foundations, drains moved, floor slab |
| Walls and roof | 3 to 4 weeks | Blockwork up, roof on, rooflights and doors fitted |
| Knock-through | About 1 week | Steel in, old back wall out, the house open to the new room |
| First fix and plaster | 2 to 3 weeks | Wiring, pipes, insulation, plasterboard, skim, screed |
| Kitchen and finishing | 2 to 4 weeks | Units, worktops, second fix electrics, flooring, paint |
Two of those rows hide a wait. Stone worktops are measured only once the units are fixed and take a week or two to arrive. And a sand and cement floor screed dries at roughly a millimetre a day, so a 65 mm screed needs about two months before a timber or vinyl floor can go down on it. Tiles can go down sooner. Ask your builder which screed they plan to use, because faster-drying mixes exist and cost more.
What stretches the programme
The ground. If building control looks into the trench and asks for deeper foundations, that is extra digging, extra concrete and often a week.
Glazing lead times. Large sliding doors are made to order. If they are not ordered on the day the opening sizes are confirmed, the shell stands finished and boarded up waiting for them.
Changes. Moving a rooflight on paper is free. Moving it after the joists are in costs days and money.
Winter. Concrete, mortar and render all dislike frost. A job that starts in November loses more days to weather than one that starts in April.
How long will you be without a kitchen?
Less time than the build. For the first half of the job the work is outside the old back wall and your kitchen carries on as normal. It goes out of use when the wall comes through, and it is typically four to six weeks from then until the new one is working. A microwave, a kettle and a washing-up bowl in another room cover the gap.
Planning the dates backwards
If you want to be cooking in the new room by a given month, count back the build, then count back the paperwork, and that is when to appoint a designer. Money follows the same calendar: builders are usually paid in stages as the work is done, so the kitchen extension cost you have budgeted is spread across those three or four months, not handed over at the start.