Basement conversions are a popular way of increasing space and square footage and adding value to your home, especially where building up is not an option. We have built several basements in Central London, allowing families to expand their living area, avoid being uprooted and save the prohibitive costs of moving home. In fact, the value to cost ratio of building a basement is more favourable than many people expect.
We thought we’d share some of our insights on the factors that will affect the cost of converting a basement.
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Existing cellar
Do you already have an existing space in your basement that you want to convert into something habitable? If a space already exists, this is the best-case scenario of a basement conversion as the heavy-lifting has already been done. The cost of converting an existing cellar into something more usable would be approximately £2000 per m2, depending on the specs you choose. The costs will increase if you need to increase the head heights or lower the floor.
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Basement excavation
If you need to excavate a basement, naturally the costs will be higher simply because the amount of work required will be more. The specific areas that will need to be costed are:
- Removal of excess material under the home. You will need to factor in digging equipment, skips and additional labour.
- Tanking and waterproofing. This is the single most important aspect of a basement conversion. Find out why.
- Underpinning walls
- Rerouting drains
- Adapting to ground conditions which may only be revealed once your builder starts excavating
- Adapting to water table levels.
You should expect the cost of a new basement excavation to be approx. £3000-4500 per m2.
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Use of Basement
What will the room be used for? This is a vital factor in determining the cost. Basements are used for a variety of rooms including, gyms, cinema rooms, garden rooms, kitchens, playrooms, swimming pools and other. The cost of building any of these will depend on the specs you specify. Obviously, installing a swimming pool, state of the art cinema room or a kitchen will be more expensive than the cost of installing a gym.
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External Access
Do you require external access to the basement? This will add to your cost as a separate entrance and full access path will have to be excavated and created. It would be more cost-effective to have access from within the house, however, that may not always be desirable if, for example, your basement is going to be used for work (consulting rooms), where you don’t want your clients going through the house.
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Other costs
There are other costs you need to consider and factor in your overall cost of build. These are costs that are usually incurred even before a single stone is broken.
- Architect Fees – Please read our guide on Choosing the Right Architect.
- Planning Applications
- Structural Engineer Fees
- Building Regulation Fees – Find out about more about Building Regulations for Basements.
- Party Wall Agreements
- Insurance
A basement conversion can add valuable space to your property, however, it’s important to consider all the elements mentioned above when you are working out the costs. If you’d like a handy tool to help you plan your project, please download our FREE project management checklist.
If you’d like to have a look at some of the basements we’ve built (and we’ve done a fair few), please visit our Projectspage on our website.
And if you’d like to pick our brains on a basement conversion you are thinking about, please do not hesitate to get in touch. You can either book a FREE consultation where we’d be happy to pop around to your property and share some of our thoughts and recommendations or give us a call on 0208 191 7595to have a quick chat.
