Single storey vs double storey extension: which is right for your home?

By HK Builders | 15 July 2026

Quick answer: A single storey extension is ideal for enlarging a kitchen or living space with less cost and disruption. A double storey extension costs more overall but is often better value per square metre because you add a second floor. The right choice depends on the space you need, your budget and how much disruption you can accept.

If you have decided to extend rather than move, the next big question is usually whether to build a single storey or a double storey extension. Both can transform how a home works, but they suit different needs, budgets and properties. This guide compares the two across the things that matter most, cost, space, disruption and value, so you can make a confident decision.

Single storey extensions

Single storey extensions are the most common choice for homeowners, and they are especially popular for creating open plan kitchen, dining and family spaces at the rear of a house. They tend to be quicker to build, less disruptive to live through, and more likely to fall under permitted development, which can remove the need for a full planning application. For many families, a single storey rear or side return extension delivers exactly the light filled, sociable ground floor space they are after.

Double storey extensions

A double storey extension adds space on two floors at once, typically enlarging the ground floor living area while adding a bedroom or bathroom above. The great advantage is value. Because the foundations and the roof serve both floors rather than one, the cost per square metre is often noticeably lower than a single storey extension. If you need both more living space downstairs and an extra bedroom upstairs, a double storey extension is frequently the most efficient way to get it.

Comparing cost

The headline figure for a double storey extension is higher, but the value per square metre is usually better. The ranges below give a sense of the difference.

Project	Indicative cost
Single storey extension	£30,000 to £70,000
Double storey extension	£55,000 to £120,000

Figures are indicative UK ranges to help you budget and are not a quote. Actual costs depend on size, specification and site conditions.

For a fuller breakdown of what drives these figures, see our detailed guide on house extension costs.

Comparing disruption and time

A single storey extension is generally the less disruptive of the two, as it usually affects one part of the ground floor and can often be sealed off from the rest of the house. A double storey project touches more of the home, sometimes including bedrooms, and takes longer to build. Our guide on how long an extension takes sets out realistic timelines for both.

Comparing value added

Both types can add significant value when they are well designed and well built. A single storey extension that creates a modern open plan kitchen is a strong selling point, while a double storey extension that adds a bedroom and bathroom can move a property into a higher bracket. The key in both cases is quality of design and build, which is why choosing the right builder matters so much. Our guide on how to choose a builder explains what to look for.

Other factors worth considering

Cost and space are the headline considerations, but a few others are worth weighing up. Light is one: a single storey rear extension with roof lights and large doors can flood the ground floor with natural light, whereas a double storey extension can sometimes overshadow parts of the existing house or garden, so the design needs care. Garden space is another; a single storey extension takes up more of your footprint at ground level, while a double storey adds much of its space upstairs and preserves more garden. Neighbours matter too, as double storey extensions are more likely to raise questions about overlooking and light, which can affect both planning and goodwill. Finally, think about how long you plan to stay, since a larger investment such as a double storey extension makes most sense when you intend to enjoy it for years to come. A good design balances all of these against your budget.

Which should you choose?

As a simple rule of thumb, if you mainly want a bigger, brighter ground floor, a single storey extension is usually the answer. If you also need extra bedrooms and plan to stay in your home for the long term, a double storey extension is often the more efficient investment. Every home and family is different, though, so the best next step is a conversation. We are happy to talk through both options for your property as part of our house extensions service, and you can see completed projects on our case studies page.

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Frequently asked questions

Is a double storey extension better value than a single storey?

Per square metre, a double storey extension is often better value, because you gain a second floor of space for a relatively small increase over the cost of the foundations and roof. However, it is a larger overall investment and more disruptive.

Which is less disruptive to live through?

A single storey extension is generally less disruptive, as it usually affects one part of the ground floor. A double storey project touches more of the home and often takes longer.

Do I need planning permission for a double storey extension?

Double storey extensions are more likely to need planning permission than single storey ones. We confirm the requirements for your property before starting.

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