How much value does a house extension add?

A well-designed house extension adds space and value to a London home. The costs page notes that a well-designed extension typically adds around 1.5× the build cost. The exact figure depends on the house, the room you add, and whether the new space joins the old plan properly.

Which type of extension adds the most value?

The type that fixes the shortage on your house. A kitchen-diner with light and a garden door is the usual strong outcome on a terrace or semi. A double-storey adds living space and a room above. The shape — rear, side return or wraparound — should follow the kitchen and the garden, not the other way around.

Does a rear extension add more value than a side return?

Not as a rule. A rear adds depth and a wider garden opening. A side return widens a thin kitchen. A wraparound is both, and is the layout that most often has room for an island, a table and a utility. The better scheme is the one that makes the ground floor work. Rear versus wraparound and the side return guide are the layout pieces.

Does a House Extension Add Value in London?

Q: Is an extension a good investment?

It is when you need the room and the house will take it. Typical bands on the costs page, standard specification including VAT: a side return £55,000–£100,000+, a rear £60,000–£120,000+, a wraparound £80,000–£160,000+, a double-storey £100,000–£190,000+. Those are ranges, not a from-£, and not a quotation. Many people stay and extend rather than move, because stamp duty, an agent and leaving the street add up. It isn't a rule. If the real shortage is a bedroom, compare a loft.

Does a house extension add value in London? Yes. A well-designed one adds space you actually use — a kitchen you can eat in, a door to the garden, sometimes a bedroom above. On our costs page we note that a well-designed London extension typically adds around 1.5× the build cost. Whether that holds on your house depends on the room you add, how it joins the old plan, and the street.

The picture is usually this. A terrace or a semi. A thin kitchen in the old rear addition. No diner. A step down to the garden. You stay put rather than move, and you want the extra room to be worth the spend — not a larger version of a poor kitchen.

Key Takeaways

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Yes — a well-designed extension adds value to a London home. The costs page notes it typically adds around 1.5× the build cost
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The stronger outcome is a usable kitchen-diner with light and a garden door, not floor area for its own sake
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Typical bands on the costs page, standard specification including VAT: a side return £55,000–£100,000+, a rear £60,000–£120,000+, a wraparound £80,000–£160,000+, a double-storey £100,000–£190,000+. Ranges, not a from-£, and not a quotation.
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A double-storey adds living space and a room above. If you need a bedroom and want to keep the garden, compare a loft
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Full cost bands sit on the extension cost guide and the cost calculator — this piece is the value picture

What Actually Adds the Value

The value is in the room you can use, not in the fact of having built out. A thin kitchen that becomes a kitchen-diner — with a table, daylight, and a door you actually walk through — is what you live with, and what a buyer reads later. A larger, dark room that still feels like a corridor doesn't do the same job.

Layout matters as much as size. The island, the diner and the garden opening need to be sketched before you freeze the footprint. How much of the 1.5× you see depends on the street and whether the new room joins the old house properly.

Worth knowing: The 1.5× figure on our costs page is for a well-designed London extension. It isn't a valuation of your house. Price the actual room.

Kitchen-Diner, Rear, Side Return, Wraparound

A kitchen-diner at the back is the usual value move on a London terrace or semi. You take the thin kitchen, add depth or width, and put cooking, eating and the garden in one room. Rear, side return and wraparound are shapes of that same job, not three different products.

A rear extension pushes the back wall into the garden. You gain depth, a wider glazed opening, and a clearer line from the house to the garden. The published band is typically £60,000–£120,000+, including VAT.

A side return fills the alley that runs along many Victorian and Edwardian terraces. That strip is often only used for bins. Building over it widens the thin kitchen enough for a proper worktop run, and on some houses an island. The published band is typically £55,000–£100,000+, including VAT.

A wraparound is both: an L-shaped ground floor. It's the layout that most often has room for an island, a dining table and a utility without stacking everything in one line. The published band is typically £80,000–£160,000+, including VAT.

The layout decision sits on the type pages, not here. Rear versus wraparound sets out when a rear-only plan is enough. The side return extension guide covers which homes a side return suits. If the room you're adding is a kitchen, the kitchen extension guide is the layout piece.

Double-Storey

A double-storey adds space on both floors. Typically a larger kitchen-diner on the ground floor and a bedroom — sometimes with an en-suite — above. The published band is typically £100,000–£190,000+, including VAT.

You're adding living space and bedroom count. That's a different job from a single-storey kitchen-diner, and a different cost. The house extensions page is the service view. For the number on your house, use the cost calculator.

Loft Conversion or Extension

People often ask which adds more value. There isn't a single winner.

An extension is the stronger route when the kitchen, the diner and the garden connection are the problem. A loft is usually the route when you need a bedroom or a bathroom and you want to keep the garden.

Cost, planning, disruption and which shortage you're actually solving sit in loft conversion versus extension. How a loft itself affects value is in how much value a loft conversion adds.

What the Work Costs

This isn't a second cost guide. Typical London bands on the costs page, standard specification including VAT: a side return £55,000–£100,000+, a rear £60,000–£120,000+, a wraparound £80,000–£160,000+, a double-storey £100,000–£190,000+. Those are ranges, not a from-£, and not a quotation. The costs page publishes project ranges, not a £/m².

Kitchens, bathrooms, flooring and decorating usually sit on top of the shell figure. The full picture — what moves the total, what sits outside the build, how long it takes — is in how much a house extension costs in London.

Many people stay and extend rather than move. Stamp duty, an agent and leaving the street add up. It isn't a rule. If you're giving up most of the garden for a kitchen you still don't like, or the real shortage is a bedroom, look at a smaller rear — or a loft.

Example Project

Full renovation, extension and loft conversion — Isleworth

This West London house was reworked as one scheme: a side extension, a double-storey rear extension, a loft conversion and a full internal refurbishment. Structural steel opened the kitchen, dining and living areas into one room. A contemporary kitchen with an island and large glazed openings sits on that ground floor. The loft added an extra bedroom.

View this project →

If you're weighing value against the house, book a consultation. We can look at the thin kitchen, the side return, and the garden you keep or lose, and tell you which scheme is realistic before you commit to drawings.

Common Questions