Two-storey extension costs explained: how much will you pay?

If you’re trying to budget for a two-storey addition to your home, you’ll need to know how much a two-storey extension costs. After all, adding an extension of this size promises more than just extra space. It can offer the opportunity to take the look back in a way that suits the way we want to use our homes in the 21st century. But, transforming a house by building on it is of course a major investment.

Whether you expansion ideas ask for a basic, good or premium spec when building an extension on two floors, it’s important to get your finances in order.

Find out how much a two-story addition can cost and compare it to a single-story version, and it can even help you decide if the sizing of your home is right for you. it is a better option than moving, which comes with its own. costs.

How much does a two storey extension cost?

In order to create a budget, it is important to be aware of what you can expect to spend. “Costs for a two-storey extension can vary greatly depending on location, complexity and quality of materials,” explains Rachel Moors, managing director of home conversion experts. Adamsons. “However, as a general guide, UK homeowners can expect the following per square metre: basic specification: £1,850 per square metre; good spec: £2,200 per sq m; premium spec: £2,600 to £3,500 per square metre. These price bands reflect the level of finish and materials used in the extension,’ she says.

As these are costs per square metre, the final bill will be influenced by whether the extension has a small, medium or large footprint, with the latter being the most expensive.

Exterior of the house with two-storey extension

(Image credit: Future/Spike Powell)

It is important to know what is included in these guide costs in order to build your budget. “Costs per square meter cover the main structure and basic features, which vary by specification level,” says Rachel, defining them as follows:

Basic: a plastered case with pendant lighting, white UPVC windows, several electrical points and a radiator.
Good: a plastered shell with recessed lighting, colored window frames (eg anthracite), designer radiators and high-quality LVT or tiled flooring.
Premium: recessed air and LED lighting, anthracite colored window frames, underfloor heating, potential Velux windows and premium interior finishes. They can also include a vaulted ceiling, oak or high-end doors, LVT or tile flooring and a fully fitted bedroom or bathroom if the budget allows.

“A reputable company should offer an all-inclusive package covering architect, design, planning and structural calculations,” she adds.

Rachel Moors

Rachel Moors is managing director of home conversion experts Adamsons, first established in 1984 by her parents Colin and Susan Moors. Adamsons is a second generation family business that has completed hundreds of double storey extensions across Greater Manchester and Cheshire.

What other costs should be considered?

In addition to the budget for the structure, you should consider additional costs. Rachel suggests the following:

Architect: £1,000 to £8,000 depending on their level of involvement, from initial design to full project management.
Structural engineer: £300 to £1,200 for structural calculations and ensuring compliance with building regulations.

And you should also set aside money for fitting out the new rooms that the expansion will create, which Rachel suggests are in the following ranges:

Kitchen: £20,000 to £60,000, depending on specification.
Bathroom: £15,000 to £35,000 for a fully fitted bathroom with premium finishes.
Bedroom: £5,000 to £12,000 depending on design and quality.

What about heating? “This is usually included in the cost per square metre, usually covering radiators or underfloor heating,” she says.

If you need planning permission for extensionthe fee is £258 in England and your local planning office can tell you the costs where you live. Although Permitted Development (PD) construction does not require an application for planning permission, it is worth obtaining a Legal Development Certificate before proceeding. Fees are usually half the cost of planning permission. The local planning authority can confirm the costs.

What factors affect the cost of a two storey extension?

A two-story extension requires more materials and more labor than a single-story version because of its proportions, and there are other factors that influence cost.

“The additional weight and complexity of the building will require more structural work,” says architect Theo Petrides, director A21architects.

Unless you’re building under PD, you’ll need formal permission and, as Theo points out, compared to a single-storey extension, ‘the project will be more prominent, so applying for planning permission will take longer and it will be more complex”.

Two storey modernist extension with brick and cladding

(Image credit: Future/Rachael Smith)

The size of a two-storey extension also influences the cost. “There will simply be more to build, more materials to get on site, more time to build and plan the job,” says Theo.

Also consider the room type and scale. “Where costs can increase is if the design includes new bathrooms on the first floor and/or a new staircase,” says architect Melanie Clear.

However, while you might think that its fundamentals would be a significant factor, this is not the case. “Nowadays, foundations are not designed for just one story, but more for soil conditions and tree preservation,” says Melanie.

Theo Petrides

Theo Petrides is a RIBA chartered architect and director of A21architects. Theo’s approach to home design and extension architecture is rooted in a deep engagement with clients to understand their unique needs and aspirations. His extensive experience of working in and around London, where space is limited, gives him the conviction that it is almost always worth expanding, with the added benefit of providing opportunities for vastly improved interior fit-outs.

Melanie Clear

Melanie is the founder of Clear Architects. She has worked on numerous projects that require reconfiguration and that sometimes means the need for a two-story extension to maximize room space. She always looks at the whole space and designs any extension as part of the overall flow rather than just an add-on.

Frequently Asked Questions

Is a two storey addition more cost effective than a single storey extension?

A two-storey extension usually costs slightly less than a single-storey version per square meter because the foundations and a roof are common to both, and what’s extra are the walls and floors. “Normally, the second floor only adds about 50% to the cost of the first, making it a more efficient choice for extending the space,” says Rachel Moors.

There are several ways that adding two floors affects costs. “With two-storey extensions, the footprint will often be the same compared to a single-storey extension, so the structural work will be similar, with the added benefit of the extra level,” explains Theo Petrides.

“Two-storey extensions also benefit from economies of scale with repeated elements and details, so you get more construction from less design work compared to a single-storey extension,” he points out.

In addition, labor costs can be reduced. “It’s generally more cost-effective to have tradesmen, from plasterers to electricians, working on a larger surface area, and they can usually work more efficiently on two levels at a time on a site, reducing labor costs per square foot” , Rachel explained.

Of course, this means the final bill for a two-storey addition is higher than a single-storey addition of similar specification, as the extension has a larger square footage, but it does mean it’s a more cost-effective option.

Will a two storey extension add value to your home?

A two-storey extension can add value to your home. Extending both the ground floor living space and adding a bedroom or bathroom upstairs is a good way to make a home worth more, and research by Nationwide has shown that an extension incorporating a large double bedroom and a bathroom can add up to 25% to the value of a three-bedroom, one-bathroom home.

However, note that the added value depends on the size and quality of the extension. Remember, too, that local circumstances matter, so it’s worth getting estate agents to value your home and suggest what its selling price might be based on what you’re aiming for.