Measure your garden before you read any further. If it is under 10 metres deep, one of these three options is probably already off the table, and knowing which changes everything that follows. Plot dimensions decide a kitchen extension far more than budget does.
The three types buy different things. Width, depth, or both, at very different costs.
Side Return: Buying Width
The side return is the narrow strip of outdoor space running alongside the back addition on a Victorian or Edwardian terrace. In most London terraces it sits somewhere between 1.5 and 2.5 metres wide, and in most houses it does nothing except collect bins and rainwater.
Infilling it converts dead outdoor space into kitchen. A galley that was 2.2 metres across becomes around 4 metres across, and 4 metres is roughly where a room stops being a corridor you cook in and starts being somewhere you can put a table.
The significant advantage is that you lose no garden. On a plot where the garden is already short, that matters more than any amount of extra floor area.
The cost characteristic is worth understanding. Per square metre this is the most expensive of the three, because you are building three new walls and a roof to enclose a small area. A 12 square metre infill at market rates of roughly £2,400 to £3,800 per square metre across the South East lands somewhere between £29,000 and £46,000 on construction alone.
Roof design is where these schemes succeed or fail. The new roof has to meet the existing back addition wall cleanly, and a flat roof with a heavy parapet detail on a period terrace tends to read badly.
Rear Extension: Buying Depth
A rear extension pushes straight back into the garden across the full width of the house. It buys depth, and it buys more floor area per pound than a side return does.
Under GPDO 2015 Class A, a single storey rear extension is limited to 3 metres beyond the original rear wall for an attached house, and 4 metres for a detached one, where permitted development rights survive. The Larger Home Extension Scheme allows 6 metres and 8 metres respectively through a prior approval route, which involves a 42 day neighbour consultation period and adds time to the programme.
Two further limits apply regardless of depth. Maximum height of 4 metres, dropping to 3 metres at the eaves where any part sits within 2 metres of a boundary. And the extension cannot cover more than half the land around the original house, counting existing outbuildings.
The trade is straightforward. A 3 metre rear extension on a 5 metre wide terrace gives roughly 15 square metres. A side return gives 12 at best. But the rear option takes 3 metres of garden and the infill takes none.
There is a design risk that people underestimate. Push back far enough and the middle of the plan goes dark, because rear glazing only lights the last few metres of a room. Beyond about 4 metres of depth, overhead glazing stops being an upgrade and becomes the thing that makes the room usable.
Wraparound: Buying Both
A wraparound combines the two, wrapping around the corner of the house in an L shape.
It solves both problems in one build programme. One set of scaffolding, one planning application, one period of disruption. And because the L shape wraps a corner, you get glazing on two sides rather than one, which is why wraparounds often feel considerably larger than their floor area suggests.
The cost premium is real and it sits almost entirely in the corner. Two roof planes meeting at right angles creates a valley that needs forming, lining and draining. Beams run in two directions and meet at a fabricated corner connection. External wall length per square metre of floor is higher than a rectangle. You are also working on two elevations at once, which means two sets of make good work where new meets old.
On planning, wraparounds sit across two different permitted development categories. The rear element falls under Class A. The side element is separate, limited to single storey, no higher than 4 metres, and no wider than half the width of the original house.
Critically, side extensions are not permitted development in a conservation area at all. Given how much London terrace stock sits within a designation, that rules out the wraparound route for a lot of properties before dimensions come into it.
The Sequence That Gets This Right
Work through these in order rather than starting from a preferred type.
First, ask what is actually wrong with the ground floor. If the answer is that the kitchen is too narrow to move around in, depth will not fix it. If the answer is that there is nowhere for a dining table and the living room is cut off from everything, width will not either.
Second, measure the garden. Losing 3 metres from a 9 metre garden is significant. Losing 3 metres from an 18 metre garden barely registers. This single measurement often makes the decision.
Third, measure the side return. Under about 1.5 metres and an infill produces a wider corridor rather than a room. It is not worth the build cost.
Fourth, check the planning position on your exact address. Conservation area status and Article 4 directions are separate controls that often overlap, and either can remove the side extension route entirely. Previous extensions also count against the 50 per cent curtilage allowance, measured against the original dwelling as it stood on 1 July 1948 or as first built if later.
Fifth, decide where daylight comes from, including overhead. This has to happen before the structure is set, because rooflight positions depend on where beams land.
Layout comes last. It is the easiest thing to change and the last thing that should be fixed. A kitchen layout chosen in week one gets redrawn when beam sizing comes back, or when planning caps the depth.
How This Looks on a Clapham Terrace
South London stock is heavily Victorian and Edwardian, typically 4.5 to 6 metres wide, with a two storey back addition and gardens that vary considerably street to street.
On a mid terrace with a short garden and an unused side return, the infill usually wins. You gain the width that actually fixes the room and keep the outside space that buyers look at.
On a plot with a longer garden and a functioning kitchen width, a rear extension makes better sense, because the problem is space rather than proportion.
Conservation area coverage across parts of Lambeth and Wandsworth is significant, and it changes the answer rather than the design. Anyone looking at house extensions clapham side of the river should confirm designation status and any Article 4 direction on the specific address before committing to a type, because a wraparound designed for a conservation area property is a wraparound that needs a full application from the start.
Extension Architecture’s approach is to settle the plot constraints and the daylight strategy before any layout work begins, since a layout drawn against the wrong extension type is a layout that gets drawn twice.
