Side Return or Rear Extension: Which Is Right for Your London Home?

Short answer: a side return gives you a better-shaped room, a rear extension gives you a bigger one. If your kitchen is a dark L-shape with a useless alley beside it, fill the alley. If the room is already square and just too small, go out the back.

That covers most cases. The rest of this is for when it isn’t obvious.

What each one actually gives you

Side return

The side return is the narrow strip running down the side of a Victorian or Edwardian terrace, between the rear outrigger and the boundary. It’s usually between 1.5 and 2.5 metres wide, and it usually holds bins, a drain and something that died in a pot.

Filling it in doesn’t add much floor area. What it adds is width — and width is what turns a corridor kitchen into a room you can put a table in. The awkward L becomes a rectangle.

It costs you no garden at all. That’s the part people undervalue until they’ve seen the alternative.

Rear extension

Straight out the back, across the full width of the house or part of it. Simpler to build, simpler to get approved, and it adds more square metres per pound than a side return does.

The trade is garden depth. Three metres out is three metres of garden gone, and on a London terrace that can be a third of what you’ve got.

Space gained — the honest numbers

A side return on a typical terrace adds somewhere around 10 to 18 square metres. A rear extension of the usual depth adds 15 to 25.

But raw area is the wrong measure here, and it’s why people who compare only the numbers often choose wrong. A side return usually transforms how the existing room works, while a rear extension mostly adds more of what you already have.

If the problem is that your kitchen is dark and badly shaped, more depth at the back doesn’t fix it — you just get a longer dark room. If the problem is that four people can’t sit down at once, depth is exactly what you need.

Cost compared

Broad London build costs, before kitchen units, appliances and VAT:

Look at those side by side and the side return seems poor value — less space for not much less money. There’s a reason for that, and it’s worth understanding rather than arguing with.

A side return is a fiddly job. Access is through the house or over a wall, because there’s no side gate wide enough for a digger. The drains are almost always in the way, so they get diverted or built over. You’re working tight against a party wall for the whole length, which means hand-digging where a machine would be quicker. And the new roof has to meet the existing outrigger wall in a way that will never leak.

A rear extension is a more straightforward piece of construction. Same materials, easier conditions, more square metres for the effort.

So the cost per square metre is genuinely higher for a side return. Whether that’s bad value depends on whether the square metres or the shape were the problem.

Planning permission compared

Both are often permitted development, but for different reasons and with different traps.

Rear extensions have clear numbers attached. Generally up to three metres beyond the original rear wall for a terrace or semi, four for a detached house, with a larger scheme available through prior approval that takes it to six and eight. Height is capped at four metres.

Side returns are usually treated as side extensions, which means the width can’t be more than half the width of the original house — rarely a problem for a narrow alley — and single storey only, with an eaves limit near the boundary.

The trap on both is the same: conservation areas remove most of these rights, and a large part of residential London sits inside one. Check that before anything else. Our planning and design team does this as a first step, because it determines whether you’re looking at eight weeks of council time or none.

Building regulations apply either way, and that’s a separate approval from planning.

Disruption and build time

A rear extension runs roughly ten to sixteen weeks on site. A side return, despite being smaller, often takes about the same — ten to fourteen — because the difficult conditions eat the time the smaller footprint saves.

The disruption is different in character. With a rear extension the back of the house opens up, usually all at once, and the kitchen is out of action for most of the build. With a side return you keep more of the house usable for longer, but you’ll have a party wall being worked against and access running through your hallway.

Neither is pleasant. Both are survivable if the sequence is planned properly, which is what our pre-construction stage is for.

When a wraparound beats both

Sometimes the answer to side return or rear extension is both.

A wraparound fills the alley and extends across the back as one project. You pay once for the scaffolding, once for the drainage work, once for the roof, and you get the shape fix and the extra depth together. If you’re already close to the budget for a generous rear extension, it’s worth pricing.

We’ve written that comparison up separately in our guide to wraparound and double storey extensions.

So which one?

Stand in the room and work out what’s actually wrong with it.

Dark, narrow, badly shaped, and there’s an alley outside — side return. Sound in shape but too small, with garden to spare — rear extension. Both problems and the budget to solve them — wraparound.

The most expensive mistake is choosing the bigger option because it sounds better value, then discovering the room still doesn’t work. Square metres are easy to price and easy to compare. Whether the room functions is neither, and it’s the thing you’ll live with.

Frequently Asked Questions

Is a side return cheaper than a rear extension?

Usually slightly cheaper in total, but more expensive per square metre. Side returns involve restricted access, drainage diversions and hand-digging against a party wall, all of which cost time. You’re paying for difficulty rather than size.

Which adds more value to a London house?

Both add value; neither reliably returns more than it cost on its own. A side return that turns an unusable galley kitchen into a proper family room often has more effect on how quickly a house sells than a rear extension that simply makes a working room larger.

Do I need planning permission for a side return?

Often not. Side returns usually fall under permitted development as a single-storey side extension, provided the width stays under half the width of the original house and the eaves height is respected near the boundary. Conservation areas are the main exception.

Can I do a side return and a rear extension at different times?

You can, but it costs considerably more than doing both at once. Scaffolding, drainage works, roof detailing and the disruption all get paid for twice. If both are likely eventually, price the wraparound before committing to either half.

How long does a side return extension take?

Ten to fourteen weeks on site for a typical job, plus design and approvals beforehand. The tight working conditions mean it rarely goes faster than a larger rear extension, despite the smaller footprint.

Will a side return affect my neighbour?

Yes, and they have rights about it. You’ll be building against or close to the party wall, which means serving notice under the Party Wall Act — two months for most work. Speak to them before the notice arrives rather than after.

Not sure which your house wants?

That’s a normal place to be, and it’s a question best answered in the room rather than over email. We’ll look at the shape, the drains, the boundary and the light, and tell you which option actually solves your problem — including when the answer is neither.

Force Builders Ltd has been building house extensions across London for over 25 years. Call 077 6525 5189.