L-Shaped Kitchen Design: Why the Return Wall Decides It

An L-shaped kitchen is the default in London for a reason that has nothing to do with taste. Most kitchens in a terrace, a maisonette or a converted flat are simply too narrow to take units on two facing walls, and the L is the only layout that gets you a second run of worktop in that space. It is chosen by elimination far more often than it is chosen on merit.

That is fine, but it means the design decisions get made in the wrong order. People pick the doors and the worktop first, then discover that the return wall is too short to be worth turning the corner for, or that the hob has ended up somewhere the extractor cannot legally vent. Both of those are decided by the plan, and both are checkable with a tape measure before anyone quotes for anything.

Why the L fits where nothing else does

Approved Document M sets 1200mm as the clear space in front of and between kitchen units, and we have set out where that figure comes from and what it means for a two-run kitchen in the U-shaped kitchen guide. Applied to an L it produces a result worth stating on its own, because the L is the only layout whose two runs never face each other:

That 600mm gap between 1.8 and 2.4 metres is the whole story of the London L. A room 2 metres wide cannot take a galley or a U without breaking the clearance, but it can take an L in both directions, because the clearance only has to be measured once. There is more on working in genuinely tight rooms in our small kitchen design guide.

The return wall has to beat 1.2 metres

Here is the calculation nobody does before committing to an L.

With runs 600mm deep, a single run along a wall of length W gives you W metres of worktop. Turn the corner onto a return wall of length R and the second run cannot start until it clears the depth of the first, so it contributes R minus 0.6 metres. Total run is W + (R - 0.6).

Against that, the corner costs you. Where the two runs meet there is a 600mm square that can only be served from one side, and whatever unit you put there stores less per metre of frontage than a normal one. Treat the corner as consuming roughly 0.6m of effective run, which is generous to the corner rather than harsh on it, and the L breaks even when R minus 0.6 equals 0.6.

That puts the break-even at a return wall of 1.2 metres. Below that, turning the corner buys you a corner problem and almost no storage. It is the single most useful number in L-shaped planning and it is nowhere in the brochures.

In practical terms: a 3.0 x 2.4m London kitchen laid out as an L gives about 4.8m of run against 3.0m for a single wall, a net gain of 1.2m after the corner. Drop the return to 1.5m and the net gain falls to 0.3m, which is one 300mm unit, and you have paid for a corner solution to get it. At that point a single run with a tall bank of storage at one end is usually the better kitchen.

The corner is 252 litres and you will not get all of it

Two 600mm runs meeting at right angles overlap in a 600 x 600mm square. That is 0.36 square metres of floor, and with a typical 700mm internal carcass height it is about 252 litres of volume sitting behind the join. It is the most expensive storage in the kitchen, because it needs either a specialist mechanism or an acceptance that you cannot reach it.

There are three honest options.

A blind corner. The cheapest. One run simply runs past the corner and the space behind the adjacent unit is reached, badly, by feeling into it. It works if you decide in advance that it is where the slow cooker and the roasting tins live, and if you never need anything from it in a hurry.

A rotating carousel. Better, and it has a hard geometric ceiling. A circle inscribed in a square can only ever cover pi/4 of it, which is 78.5 per cent. So a carousel reaches at most about 198 of those 252 litres, and roughly 54 litres stay in the four square corners no matter how good the mechanism. That is the arithmetic, not a manufacturer’s caveat.

A pull-out corner mechanism. The type that swings the front shelves out and slides the rear ones forward. These reach closer to the full volume and are the only option that gets everything to the front, and they are the most expensive per litre of anything you will buy for the kitchen.

Whichever you choose, do not put the corner where you work. Our kitchen corner units guide covers the mechanisms in detail, and the carcass sizes that drive all of this are in the kitchen cabinet dimensions guide.

Where the hob goes, and the hood that does not comply

This is the one that costs money after the kitchen is in.

Approved Document F asks for 30 litres per second of extract with a hood venting outside, or 60 without, and states in terms that “a recirculating cooker hood on its own does not provide a means of ventilation that complies with Part F of the Building Regulations”. We have covered those rates and what they mean for an open-plan room in the open-plan kitchen guide.

What is specific to the L is that the layout decides where the hob can go, and it usually decides badly. The L pushes the hob onto whichever leg has the room, and in a London terrace one of those legs is very often the party wall. That matters more here than in any other layout because the L pushes the hob onto whichever leg has the room, and in a London terrace one of those legs is very often the party wall. you cannot duct through a party wall, and you cannot duct through a neighbour’s flat. In a mid-terrace or a flat conversion that leaves three options: a long horizontal run to the nearest external wall, a ceiling void that may not exist, or a recirculating hood that does not comply on its own.

Decide the hob position from the duct route, not from the plan drawing. If the only workable route is short and straight on one leg of the L, that leg has the hob, and everything else arranges itself around it. Doing it the other way round is how a kitchen ends up with a five-metre duct run, a hood that never clears the steam, and a plasterboard bulkhead nobody wanted.

Two details from the same document decide whether the hood works once it is in, and both are routinely missed:

• The hood should span at least the full width of the cooker (note to Diagram 1.1). A 600mm hood over a 900mm hob is undersized by the document’s own standard, and it is a very common specification.
• Where the manufacturer gives no figure, the hood should sit between 650mm and 750mm above the hob surface (paragraph 1.21). Higher than that and the capture rate falls away; lower and it is in the way.

The refurbishment clause worth knowing

If you are replacing an existing kitchen rather than building a new one, Approved Document F is gentler than most people assume. Paragraph 3.30 says that where building work is carried out in a kitchen, “any existing fans (including cooker hoods, where they extract to the outside) should be retained or replaced”. Paragraph 3.31 then adds: “If there is no ventilation system in the original room, it is not necessary to provide one in the refurbished room.”

So a straight refit of an old London kitchen that never had extract is not forced to add it. What you cannot do is remove or downgrade what was already there. Paragraph 3.32 adds that if an extractor fan or cooker hood is replaced and uses the existing cabling, it does not need to be notified to building control.

None of this is an argument for skipping extract. A kitchen without it is a damp kitchen. It is an argument for knowing which parts of the specification are legally fixed and which are yours to decide, which changes what you should be paying for.

Getting the rest of the plan right

Put the sink on the longer leg, under the window if there is one, and keep the dishwasher immediately beside it on the side you do not stand. The sink is the busiest point in the kitchen and it wants the run with the most space around it.

Keep the corner between the sink and the hob, not beyond them. If your working stretch crosses the corner every time you cook, the layout is fighting you. Sink on one leg, hob on the other, and the corner sits inside the triangle where it does least harm.

Only add an island if the return leaves you 1200mm clear on every side. With 600mm runs and the AD M figure, that needs a room roughly 3.6m wide before an island is anything other than an obstacle. The kitchen island guide has the dimensions.

Sort the services before the units. Moving a soil stack, a gas run or a consumer unit is the difference between a straightforward fit and a significant job, and in a flat it may need the freeholder. Our London kitchen design cost guide and the new kitchen cost guide cover where the money actually goes.

Frequently asked questions

What is the minimum room size for an L-shaped kitchen? About 1.8 metres in both directions. That is a 600mm-deep run of base units plus the 1200mm clear space that Approved Document M, Volume 1 paragraph 2.24(b) requires in front of and between kitchen units. The same figure means a galley or U-shape needs 2.4 metres, which is why the L is the layout that fits London rooms nothing else fits.

Is an L-shaped kitchen always better than a single run? No. Turning the corner only gains you worktop once the return wall is longer than about 1.2 metres. Below that, the second run contributes less than the corner unit costs you in usable storage, and a single run with tall units at one end usually gives a better kitchen for less money.

How much storage do you lose in a kitchen corner? The contested space is a 600 x 600mm square, roughly 252 litres of carcass volume. A rotating carousel is limited by geometry to about 78.5 per cent of a square it sits inside, so around 54 litres stay unreachable however good the mechanism. A blind corner loses considerably more in practice, because you cannot see into it.

Can I put the hob on the party wall in an L-shaped kitchen? You can position it there, but you cannot duct through a party wall, so the extract has to run horizontally to an external wall or through a ceiling void. If neither is possible you are left with a recirculating hood, and Approved Document F states that a recirculating hood on its own does not comply with Part F. Work out the duct route before you fix the hob position.

Does a new kitchen need an extractor by law? For new work, Approved Document F Table 1.1 asks for 30 litres per second with a hood venting outside, or 60 litres per second without. For a refit, paragraph 3.31 says that if there was no ventilation system in the original room it is not necessary to provide one, though any existing fan or externally venting hood must be retained or replaced. Regardless of the rules, a kitchen without extract is a condensation problem.

Where should the sink go in an L-shaped kitchen? On the longer leg, ideally under a window, with the dishwasher next to it. Keep the sink and the hob on different legs so the corner falls between them rather than at the end of your working stretch, and never put the sink immediately next to the corner, where the adjacent door or drawer will foul it.

Regulation text quoted from Approved Document F, Volume 1, 2021 edition and Approved Document M, Volume 1. Run-length and corner figures calculated for 600mm-deep units. Checked 27 August 2026.