How Long Does a Kitchen Extension Really Take? 17–18 Weeks, Not 12

Ask three contractors how long your kitchen extension will take and you will very often hear the same answer: twelve to thirteen weeks. It is a comfortable number. It sounds professional, it fits inside a season, and it makes the quote easier to say yes to.

In my experience, on a straightforward single-storey kitchen or side-return extension in South West London, with no serious surprises, the realistic build time is seventeen to eighteen weeks.

That is not pessimism and it is not padding. It is what the work actually takes once you count the things a programme on paper tends to leave out — inspection hold points, drying times, lead times, and the ordinary gaps between one trade finishing and the next one starting. Almost every project I run lands in that window. Very few land in twelve.

Where the four to five "missing" weeks actually go

Here is roughly how seventeen to eighteen weeks breaks down on a typical job:

• Set up, strip out and demolition — 1–2 weeks. Scaffold, protection, waste, and taking down whatever is coming down.
• Groundworks and foundations — 2–3 weeks. Digging, building control inspections at open-hole stage, concrete, drainage runs and connections. This is the stage most exposed to weather and to whatever is found in the ground.
• Brickwork, blockwork and steels — 3 weeks. Up to damp-proof course, then up to wall plate, plus installing the structural steel and forming the opening into the existing house.
• Roof structure, deck and covering — 2 weeks. Joists, deck, membrane, rooflights, and getting the building watertight.
• Glazing installation — 1 week on site. But the lead time behind it is usually eight to twelve weeks from order, which is why the order has to be placed early, not when the opening is ready.
• First fix and insulation — 2–3 weeks. Electrics, plumbing, underfloor heating, insulation, plasterboard.
• Plaster and screed, plus drying — 2 weeks. This is genuinely uncompressible. Screed and plaster dry at the rate they dry at, and rushing what goes on top of them is how you get cracked tiles and lifting floors.
• Kitchen installation — 2 weeks.
• Worktop template and fit — 1–2 weeks. Templating cannot happen until the cabinets are actually in and level, and stone fabricators typically need ten to fifteen working days after that. Almost every optimistic programme I see has quietly forgotten this stage exists.
• Second fix, decoration and snagging — 2 weeks.

Add those up honestly, allow for the fact that trades hand over to each other rather than teleport, and twelve weeks stops looking like an ambitious target and starts looking like a different job entirely.

Why the optimistic number costs both sides

A twelve-week promise is not usually dishonest. Most contractors genuinely believe it when they say it — they are pricing the work, not the waiting, and the waiting is invisible until you are in it.

The problem is what the number does once it is said out loud.

The homeowner plans their life around it. Removals, a rental, school holidays, Christmas, grandparents visiting, the tenant moving out. When week twelve arrives and the plasterer has not started, none of those things move for free.

The builder starts defending the programme instead of building. By week six they know they are behind. From that point on, every conversation is about the delay rather than about the decision that actually needs making. Trades get overlapped that should not overlap. Corners appear — not out of malice, but because the fastest way to look on-programme is to stop doing the parts nobody inspects.

The relationship sours. This is the part that costs the most and shows up on no invoice. A project where both sides expected eighteen weeks and delivered eighteen weeks ends with a handshake. The identical project, sold as twelve, ends in a stand-off about who is to blame — and a homeowner who will not recommend a builder who actually did decent work.

The tension is manufactured entirely by the gap between the promise and the reality. Close the gap at the start and most of it never happens.

What I do about it

Setting an honest programme is only the first part. The seventeen to eighteen weeks then has to be protected, and that is the actual job.

I resolve day-to-day problems quickly. Something unexpected turns up on nearly every site — a drain run where the foundation needs to go, a wall with no foundation under it, a delivery short of two lintels. The cost of these is rarely the fix itself. It is the days the site sits half-working while everyone waits for someone to decide. Being reachable, being on site, and giving a straight answer the same day is what stops a two-hour problem from becoming a two-week one.

I make sure decisions are made in time. Tiles, taps, sockets, worktop, handles, the exact position of the extract. Every one of those has a last responsible moment, and it is usually weeks earlier than homeowners expect — the electrician needs the lighting layout before first fix, not when the plasterer arrives. I work the decision schedule backwards from the programme and chase it, so a choice nobody realised was urgent never becomes the reason the site is standing still.

I bring subcontractors in at the right time. Too early and they are on site with nothing to do, which you pay for one way or another. Too late and you have a gap, and their next job has already started. The skill is not booking the trades, it is sequencing them — and knowing that the glazing has to be ordered in week two even though it does not go in until week eleven.

I source the best price. Kitchens, glazing, sanitaryware, flooring and tiling are where the money is, and where a builder's supply markup is least visible. Buying those directly at trade prices, rather than through a supply-and-fit line on a quote, routinely saves more than my fee — and because I am ordering them, they are ordered early enough that the programme is never waiting on a delivery.

The honest version is the cheaper version

There is nothing clever about a long programme. The point is not that eighteen weeks is better than twelve — it is that eighteen weeks told at the start is dramatically better than twelve weeks that quietly becomes eighteen anyway.

The first version lets you plan, budget and stay on good terms with the people building your house. The second version costs you the same time, plus the stress, plus the arguments, plus whatever gets rushed at the end to make the number true.

If you want a realistic programme for your own extension before you sign anything, have a chat. There is no obligation and no fee for the conversation — I am happy to tell you what I think it will actually take, even if you go on to run it yourself.

Common questions

Is 12 weeks ever realistic? Occasionally — a very small, very simple extension, a builder with the whole team free, no glazing on a long lead time, and every decision already made before the first spade goes in. It is not the normal case, and it is not what most twelve-week quotes are describing.

Does the 17–18 weeks include planning and design? No. That is the build only, from first day on site to snagged completion. Design, planning permission, party wall notices and tendering sit in front of it and typically add several more months — I have written a full breakdown in how long an extension or loft conversion actually takes.

What pushes a kitchen extension past 18 weeks? Usually one of four things: something structural found once the ground or the existing wall is opened up, a long-lead item ordered late, a run of bad weather during groundworks or roofing, or decisions arriving after the trade that needed them has already left site. The last two are the ones most within anyone's control.

Can I live in the house during it? Most people do, with a temporary kitchen. It is manageable for a single-storey rear extension because the works are largely outside the existing footprint until the wall comes down — but plan for two or three genuinely disruptive weeks around the structural opening and first fix.