Extensions · South & West London
House extensions in London: four kinds, and the hard part is knowing which one your house wants
We build side return, rear, wraparound and side-and-rear house extensions across south and west London. Our completed projects show the structural and layout decisions; a free site survey helps establish which options suit your property.
Side return, rear, wraparound, side and rear. They are not interchangeable, and the right one depends on the shape of your house rather than the size of your budget.
More house, without moving
An extension is the usual way to get more house without moving, and in London it is normally the cheaper option by a wide margin — no stamp duty, no agent, no chain. What it is not is quick or simple, and anyone who says otherwise is selling something.
Ground floor extensions are the bulk of what we build: side returns, rears, a wraparound, and a side and rear, on terraces and semis across south and west London. The difference between them is not scale, it is geometry — and choosing wrongly is how people end up with more floor area and a worse house.
The question worth asking at the outset is not how much bigger the house gets. It is what shape the ground floor ends up in, and what happens to the rooms the extension is attached to. Every extension takes something from the rooms behind it. The design either accounts for that or ignores it.
Four types, and what each one is for
Side return
The alley down the side of a Victorian terrace is dead space. Nobody sits in it, nothing is stored in it, and it is doing nothing except keeping the kitchen narrow. Filling it squares the ground floor into a single room across the width of the house. On a side infill in SW18 the whole point was to make the room wide enough for an island to sit at the centre rather than pressed against a wall, which is the actual difference between a galley you pass through and a room the household lives in.
Rear extension
Straight out into the garden. This is the type that buys depth, and depth is the thing to be careful with: past a point you are trading a bright garden-facing room for a dark middle of the house. On a family home in Richmond a rear extension let the living room grow, merged the kitchen and dining area into one room over the garden, and made space for a ground floor bathroom — the least photogenic thing in the project and the one the household would miss first.
Wraparound
Side return and rear combined in one build. The groundwork, the scaffold, the party wall process, the structural design and the disruption are shared once rather than paid for twice. On a mid-terrace in Merton we removed a tired conservatory and extended the full width of the rear, producing an open plan kitchen and dining room with a ground floor WC folded into the design. If there is any prospect of eventually wanting both, doing them together is almost always the better decision — not because the build is simpler, but because doing it in stages means living through the whole process twice.
Side and rear
The largest thing we build on a ground floor. On a family home in SW18 it bought a utility room, a pantry, a ground floor WC and an open plan run of seating area, kitchen and dining space. Those unglamorous items are the ones people ask about after the job is finished and it is too late to add them.
Permitted development or a planning application — and sometimes both
Many single-storey rear extensions fall under permitted development, which means no planning application, although prior approval may still be required and the rules are tighter on flats, in conservation areas and on listed buildings. Anything larger, or a wraparound, usually needs a full application through your borough.
The two are not mutually exclusive. On a house in SW18 we took what permitted development allowed at the rear and applied for planning permission on the side, which produced a wraparound larger than either route would have permitted on its own. It is not a loophole and it is not unusual. It is simply an option most people are never offered, because it takes more work at the drawing stage than defaulting to one route.
If a builder tells you your extension is limited to what permitted development allows, ask whether a combined approach has been looked at. It changes the drawings, the time before work starts and who needs to be involved, so it is a conversation to have at survey stage rather than after somebody has already submitted something.
You will need building regulations approval whichever route you take. If you are attached to a neighbour, or building up to a shared boundary, you will need a party wall agreement — a legal process with fixed notice periods, and the most common single reason a start date slips. We handle building control, and we will tell you when a party wall surveyor is needed rather than leaving you to find out.
The order things happen in
- Set up and protection, then demolition and groundwork
- Foundations, structure and steels, then the roof
- Watertight: glazing in, first fix plumbing and electrics
- Plastering, second fix, kitchen and flooring
- Decoration, snagging and building control sign-off
The sequence matters because several decisions have to be settled well before the trade that depends on them turns up. A kitchen layout has to exist by first fix, because the sockets and the waste runs follow it. Underfloor heating goes in before the slab and is one of very few things that genuinely cannot be added later without starting the floor again. Glazing carries the longest lead time on the job, and full-width glazing changes the structural design, so it has to be settled before steel is ordered rather than after.
You get a fixed, itemised quotation after the survey and the drawings, not an estimate over the telephone. During the build there is one team, one project manager and a weekly update. We tell you about problems on the day we find them, and we tell you before the work is done when something we have found changes the cost.
What actually moves the work
Structural complexity. A single opening across the full width of a house asks considerably more of the beam over it than an opening with an intermediate support. That affects its size, how it is supported at each end and how it is concealed within the ceiling. It is settled by the structural engineer long before anyone chooses a door.
Glazing. Slim-framed crittall-style doors and large rooflights are the two things that most often lift a specification, and the two things people most want. Think about where the doors go when they are open: bi-folds stack to one side and that stack has to live somewhere, sliding doors leave a fixed panel, and hinged crittall-style doors need swing space. All three look identical in a photograph taken with them closed.
What is already on the site. Building on a conservatory base is almost always a false economy. Those bases are built to carry a lightweight glazed structure, not a masonry wall with a solid roof and a floor above it, and they are typically shallow and often unreinforced. Assume the foundations are being redone and treat it as good news if the survey says otherwise.
What is behind the plaster. On a Victorian house nobody knows until it is off, and a neighbour's drainage will be found somewhere it does not appear on any drawing. That is normal. What matters is whether your builder has a plan for it and tells you the day it happens.
Finish. On a side return in SW17 the owners asked for exposed brick and exposed steel rather than plasterboarding everything, which costs less than covering it all up. But it is a decision made at drawing stage: steel that will be seen has to be specified, finished and fire-protected differently from steel that disappears behind boards, and brickwork on show has to be laid to a standard plaster would have forgiven.
Common questions about house extensions in London
Do I need planning permission for a house extension in London?
Often not. Many single storey rear and side return extensions on a London terrace fall under permitted development, which means no planning application. You lose those rights if the house has already been extended, if it is a flat, if it sits in a conservation area, or if the council has an Article 4 direction covering your street. We check which of those applies to your address before any drawings are made, because the answer changes what is worth designing.
What is a side return extension?
A side return extension fills the narrow alley running alongside the back room of a Victorian or Edwardian terrace. That strip is usually wasted ground, and building across it widens the rear of the house rather than lengthening it. It is the most common extension on a London terrace because it gains useful width without taking much garden.
What decides how long a house extension takes?
The structure, the ground and the services, rarely the building itself. A wide opening needs steel, and steel needs fabricating and temporary support before it lands. Shallow foundations next door mean deeper digging. Moving a soil stack or a gas main brings in a third party who works to their own schedule. Waiting on a decision, a survey or a utility is usually the slow part.
Can I stay in the house while an extension is built?
Usually yes for a ground floor rear or side return extension, because the work happens outside the existing wall until the opening is formed. The disruptive period is short and predictable, and it is the point at which the kitchen is out of use. We tell you when that window falls before work starts, so you can plan around it.
Do you handle party wall agreements?
Yes. Excavating near a neighbour’s wall or building up to the boundary triggers the Party Wall etc. Act, which means serving notice on the adjoining owner. We tell you at survey stage whether your job triggers it, and we work with the surveyor so the notice period runs alongside the design rather than after it.
See the work in real homes
Side and rear ground floor extensionView the project →
Ground floor wraparound extensionView the project →
Start with a survey, not a guess
Book a free site survey. We will tell you which of the four types your property suits, whether permitted development gets you there, and what your existing rooms will be like once the extension is on. There is no obligation afterwards.
“Communication is second to none, always providing proactive and transparent updates.”Dylan Titherley · Read the Google reviews
From the portfolio
Extensions we have completed
Wandsworth, SW18 · Side & rear extensionSide and rear ground floor extensionTwo planning routes, used together, to get one bigger extension.
Merton, SM4 · WraparoundGround floor wraparound extensionOne trip round the back, rather than two jobs a few years apart.
Richmond, TW2 · Rear extensionGround floor rear extensionA downstairs bathroom, which changed the house more than the extra room did.