As moving gets more and more expensive, people are looking to improve their homes rather than go through the hassle of trying to find a cheap mortgage and spend money on stamp duty. One way to improve your home and give you more space is to build a single storey extension.

On average, a single storey extension costs £1,800-£3,000 per square metre to build – but a number of factors can affect the cost. Let’s take a deeper look into how much a single storey extension costs.

How much does a single storey extension cost?

A single storey extension is a ground-floor extension that is usually built at the back or the side of a property, although these are often called side return extensions. People often use single storey extensions to extend their kitchen, create a second living room or add a study to their homes.

For an average 20 square metre single storey extension, expect it to cost anywhere between £36,000 and £60,000. This price includes labour and materials, but usually won’t include decorating or plastering.

HaMuch has a large database of hourly and daily rates for extension builders across the country, so make sure you take a look at our table further down the page to get an idea of how much the average single storey extension will cost in your area.

The larger you build your extension, the more likely it is that you will make some savings on material costs. Here’s how much to expect to spend on larger extensions:

30 square metres: £54,000-£84,000

40 square metres: £70,000-£104,000

50 square metres: £90,000-£125,000

Single storey extension cost calculator

When you decide build a single storey extension, you need to be aware of other costs involved. While our price estimates above include all your internal stud walls, utilities, electrics, windows and doors, there are some costs that won’t be included.

Our cost calculator below can help you work out the total cost of your single storey extension:

Job type	Average cost
Single storey house extension	£1,800-£3,000 per square metre
Plastering	£10 per square metre, plus £100-£150 per day
Painting and decorating	£9-£18 per square metre (not including paint)
Carpet fitting	£5-£10 per square metre (installation only)
Wooden flooring installation	£20-£30 per square mere (fitting only)

What size single storey extension can I build without planning permission?

Single storey extensions are permissible under permitted development rights, meaning you don’t have to apply for planning permission. There are different rules for side extensions and rear extensions:

Side extensions

• Must have a maximum height of 4 metres

• Must not exceed half the width of the original house

• Must not face the road

Rear extensions

• Must not be longer than the rear wall of the original house by more than 3 metres for a semi-detached house, or 4 metres for a detached house

• Must not exceed 4 metres in height

You can also use a rule called ‘prior approval’ to double your allowance for a single storey extension, allowing you to build a single storey extension of up to 6 metres for a semi-detached house or 8 metres for a detached house.

Do I need an architect for an extension?

There’s no law to say that you have to have an architect to build an extension. If your single storey extension is a simple extension with no special eco features or no party wall issues, you might be able to get away with not employing an architect.

However, it’s always good to have designs or drawings done before you start an extension project. You can hire architectural designers that cost slightly less than a registered architect to help you design the best extension based on your budget, advising you where you can save money. They can also help you with planning permission applications, building regulations and more, so it might still be worth looking for someone to advise you.

How deep do foundations need to be for a single storey extension?

Your builder should have all this in hand, but for a single-storey extension using strip foundations, the concrete foundation base should be a minimum of 150mm. The trench itself should be at least 1 metre deep with the brickwork sitting on top to make it up to 50mm.

If you have trees near your property, you may need to have deeper foundations. The general rule is if you have a tree within 30 metres of where you want your single storey extension, your foundations will need to be deeper. This is because deep roots can affect the moisture in the soil that supports your property.

Is it cheaper to have an extension or a conservatory?

It’s normally cheaper to build a conservatory than an extension, because you usually don’t have to apply for any type of planning permission and may not have to have building regulations sign-off. However, it’s worth remembering that a conservatory isn’t as versatile as an extension. Conservatories are made mostly of double glazing, so they can get very hot in the summer months. In the winter, they can be too cold to enjoy because they’re poorly insulated.

If you want to use your new single storey extension all year round, you might consider that an extension is more cost effective as you’ll get more use out of it. It’ll also depend on what you want to use your room for – for example, if you want your extension to be a bedroom, a conservatory won’t be suitable. However, if you want it to be an extension of your kitchen, a conservatory could offer good value for money.

If you’re ready to kick off your single storey extension project, post your job on HaMuch now to get in touch with available builders in your area that can give you a quote.

Estimates for common extension builder jobs;

Rates for other trades