Side return or rear extension: how to choose

Most people arrive at this decision with a shape in mind, not a problem. They have seen a side return in a neighbour’s house. Or they saw a rear extension in a magazine. They want that. The better question is which one your house is actually asking for.

They are not interchangeable. They cost different amounts and take different routes through planning. They solve genuinely different problems.

What each one actually is

A side return fills in a narrow alley found on Victorian and Edwardian terraces. The alley runs along the back half of the house. It is the strip of dead ground beside the original back addition. You are not pushing into the garden. You are claiming land you already own and currently use for nothing.

A rear extension pushes the back wall of the house further into the garden. You gain depth across the full width of the house. You lose garden in exchange.

A wrap around does both. It is a side return and a rear extension in one build. It is the option most often chosen when the ground floor must change completely. It is not about getting bigger.

The costs

Both are priced as a build rate per square foot of new space. Our own rates cover a rear extension, side return, wraparound and loft. They also cover a full renovation and a basement. They are published by specification in the NU Build Cost Calculator. Take the band from there before you compare any quote.

The side return costs more per square foot than a rear extension. That surprises people, because it looks like the smaller job. The reason is structural. A side return usually means removing a substantial part of the original external wall. The load above it is then carried on steel. A rear extension often leaves more of the existing structure intact.

In London, a loft conversion is normally the least expensive way to add space. The roof and the walls are already there. A basement is the most expensive, because neither is.

Those are London rates for the standard of work we do. They are not national averages. They are not the cheapest quote you will find.

For the detail behind two of those bands, see rear extension cost in London. Also see loft conversion costs in London.

How to choose

Choose a side return if the back of your house is dark. The kitchen is narrow, and there is a useless alley beside it. This is the classic London terrace problem. The side return is the classic answer. You keep your garden. You get width where the house currently pinches.

Choose a rear extension if the garden is deep enough to lose some. What you need is a bigger room rather than a wider one. A rear extension gives you depth across the full width. That suits a house that is already reasonably wide but shallow at the back.

Choose a wrap around if the whole ground floor is wrong. You must also be prepared to rebuild how it works. It costs the most and disrupts the most. Of the three, only it genuinely changes the plan of the house. The others add to it.

The three things people underestimate

Light is not a function of floor area. A badly glazed extension can make a kitchen darker. It buries the original back window under a new roof. Where the glass goes matters more than how much of it there is.

The party wall is a process, not a formality. You may be building up to or along a shared boundary. If so, you will need a party wall surveyor. Your neighbour will need notice. Start that conversation early and it is administration. Start it late and it is a delay.

Planning is not the only permission. Building control and structural calculations sit alongside it. On many terraces, so does your neighbour’s agreement. A scheme can have planning permission and still not be ready to build.

The party wall process is explained in our guide. Read party wall agreements, what they cost and who handles them.

Which one adds more value?

The honest answer is that neither adds value reliably on its own. What adds value is a ground floor that works. So do light where you spend time and storage where you need it. So does a plan that suits how the household actually lives. We have seen small, well-resolved side returns outperform large, poorly planned rear extensions.

If the extension is the whole plan, it is usually the wrong plan.

How we approach it

We are a design and build contractor in Fulham, West London. We work across Chelsea, Kensington, Fulham and the surrounding prime postcodes. Architecture, interior design, project management and construction sit under one contract. So whoever designs your extension is accountable for what it costs to build.

You may be choosing between a side return and a rear extension. If so, we would rather look at your house than guess. That conversation costs nothing.

Weighing a side return against a rear extension on a specific house? Fill out the contact form or call 020 7731 6841. Let’s get you booked in for a free call with Nick. Send us the area and the footprint. We will tell you honestly what we would do with it.