How much is an extension going to cost?

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How much is an extension going to cost?

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Ground Floor Extension, Drury Rd Casas de estilo clásico de London Building Renovation Clásico
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Home extension costs can skyrocket quickly if you're not careful and worse still, projected extension costs could put you off considering improving your home altogether and that simply won;t do, which is why we thought it would be helpful to put together a comprehensive guide to building an addition. After all, we can all use a little extra space in our homes, whether for a new kitchen or a larger living room, and we must not let rumoured extension costs per sq ft stop us from putting out some tentative feelers with a few architect firms! Whatever your questions about home extensions and their assumed costs, we think we have the answers for you, right here, so let's take a look!

1. A simple extension on the ground floor.

Ground Floor Extension, Drury Rd Casas de estilo clásico de London Building Renovation Clásico
London Building Renovation

Ground Floor Extension, Drury Rd

London Building Renovation

As a general rule, we suggest that you estimate your extension costs per sq ft to come in at between 600 and 750 dollars. This is a pretty accurate assessment of how costs have increased in recent years, but don't forget that the location of your property will also play a part, as urban locales always cost more than rural ones with easy and expansive access options. In order to give an idea of what an averagely sized single-storey extension of 12 x 6 feet would amount to, we think you should get comfortable with amounts in the region of around 40,000 – 55,000 dollars, plus the additional costs such as architects' fees, registration and any taxes.

2. Two-storey extensions.

The Cube, Winchester Casas modernas de Adam Knibb Architects Moderno
Adam Knibb Architects

The Cube, Winchester

Adam Knibb Architects

The same calculation used for single-storey extensions can also be applied to those that extend over several floors. Naturally, an extension over two floors would increase by 50 per cent of the costs and would be a minimum of around 50,000 dollars, plus the additional costs mentioned above. How simple or convoluted your design is will have a huge impact on your home extension costs and if structural concerns need to be addressed or altered, we could be talking BIG money! Especially if load-bearing walls are involved!

3. A new kitchen or bathroom extension.

Bright, clean, contemporary Cocinas de estilo moderno de homify Moderno

Bright, clean, contemporary


When a space is being adapted to house a new kitchen or bathroom, it's a given that your home extension costs will increase. For a bathroom, you should expect to spend an extra 10,000 – 12,000 dollars, for new sanitary ware, tiles, plumbing and electricity, but kitchens will cost more. For a small or average kitchen, we think you need to have around 15,000 dollars extra to play with.

4. Details to consider within your extension.

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If you're going to be investing a fair amount of money in a new home extension project, you need to be sure that you're not going to do the final result an injustice by choosing subpar materials and installations. It's the main features that need to be gorgeous, such as kitchen worktops and suite items!

5. What if I have difficult conditions?

Existing 1900s Family Home in Hindhead, Surrey de ArchitectureLIVE Moderno

Existing 1900s Family Home in Hindhead, Surrey


Alas, not every home extension project is straightforward or easy to complete, which means that extra costs will be incurred. Common issues include:

- Every extension needs a solid foundation. Depending on your soil type and ground conditions, these can be realized either simply or through complex activities. 

- Is access to the construction site simple or complicated? If access is limited or tricky, you can expect your home extension costs to increase, significantly!

- Will the structural conditions or walls, roof areas or windows have to be changed?

- Which pipelines and drainage systems must be modified during the extension process.

6. Think about how location impacts on your design.

Forest View Balcones y terrazas de estilo moderno de Clear Architects Moderno
Clear Architects

Forest View

Clear Architects

You might not realize this, but the location of your home might play a far larger role in your extension design than first thought! If your house is in a premium location, for example, in a sought after neighborhood or district with great infrastructure, it is worth investing a bit more in your extension, to get the right look.

7. Materials and construction will have an impact.

What you decide to build your extension out of will have a dramatic impact on how much the finished project actually costs! This really is one of those 'how long is a piece of string' questions and we dread to think how many times architects are asked 'how much is an extension?', as bricks will incur a different cost to wood and a standalone extension will be impossible to match up to a lean-to cost!

8. How to manage the costs.

Modern Garden Room Anexos de estilo moderno de ROCOCO Moderno

Modern Garden Room


In order to manage your extension project in the best possible, in terms of time and costs, it makes sense to involve a professional architect right from the start. Bringing experience, expertise and professional contacts into the mix, your architect will be an invaluable source of money-saving potential. For example, an architect can call in a number of deals from various craftsmen, in order to compare alternative plans and costs and this give us, as the homeowners, a bit more security as to what the final price will actually be. To avoid nasty surprises and unexpected extension costs, it makes sense to always have contracts in place with your craftsmen and builders and again, your architect can help with this.

For some extension inspiration, take a look at this article: A kitchen extension to end them all!

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