Basement conversion

Basement conversions are a popular method of increasing your home’s living space, particularly in urban areas where there is less space for conversions. Depending on the state of your basement a conversion can be relatively cheap, though many jobs require excavating additional space beneath your home to make sure there is enough headroom, and can add thousands of pounds to a quote. The key is careful planning in order to get an approximate estimate of the costs of a basement conversion and to avoid potential problems taking you by surprise.

Is my property suitable for a basement conversion?

Existing cellar

If your property already has a cellar, converting it from a storage room into living space can be a relatively simple and cheap procedure.

Excavating additional space

To make your basement liveable your conversion may require the excavation of the basement floor. In this case there will be a lot more factors to consider: waterproofing your basement, party walls, removing your ground floor, and so on. These conversions are much more expensive and will take a greater amount of time.

Doing work that alters the volume of your property will likely require planning permission. It is best to discuss this with your tradesmen. Be sure to do a Full Plans Application rather than sending in a Building Notice, as this will take all necessary factors into account in advance.


Things to consider for my basement conversion

Cost vs value

Basement conversions are becoming much more popular in urban areas as a way of creating more living space. They can add a lot of value to a property, but you will need to compare the cost of the conversion against property values in your local area. The properties in your location may have maximum values, which you are not likely to be able to go over regardless of how much money you invest. The best things you can do are talking to a local estate agent and looking at examples of previous conversions in your area. These should be available on the websites for tradesmen and companies specialising in basement conversions and you may even be able to find out how much these particular jobs cost.

How much do basement conversions cost?

Simple conversions

It may be that your current basement or cellar is suitable to be converted without the need for any excavations. In this case, you could expect to pay around £750 to £1200 per square meter.



Excavating additional space in your basement in order to accommodate a conversion can be very expensive; more so if you run into certain obstacles.

If your ground floor is a concrete oversight slab, rather than traditional floor joists, then it will need to be removed for the conversion process and replaced. You may need to divert your property’s drains. The ground around your property can also cause problems, such as if it is made up of solid stone, clay or sand. If your area has a high water table, your tradesmen may need to keep pumping the basement dry during the conversion.

As a minimum, a basement conversion requiring excavations can cost between £2000 and £3000. Any of these problems can add thousands to your quote. You will also need to pay to have your basement properly waterproofed.

Do your research beforehand and have a budget in place. Once you have spoken to an architect or other specialist and have an estimate, make sure you can match it. Waiting to begin your conversion will be better than going through with it without the necessary funds.


What planning permissions are required for basement conversions?

Once again, things are much simpler if you have an easily-convertible basement already in your home. If you are just renovating a basement like this you should not need planning approval.

A conversion requiring excavation work will almost certainly need planning permission as you will be altering the structure and volume of your property.

You will almost certainly need Building Regulations approval. Building Regulations cover the minimum standards for construction work to ensure that your building is sufficiently safe, hygienic and energy efficient. You may be exempt from this rule if you are just renovating an existing basement. You will also need to deliver a building notice to your local council. An inspector will come to survey your conversion multiple times, and at the end of the project should provide you with a completion certificate.

If you share walls with a neighbour you will need to seek a party wall agreement to make sure your conversion work does not disrupt their property. If you fail to inform your neighbour about your conversion work and reach an agreement on it, the work can be suddenly halted.basement

Before beginning the conversion, submit a Full Plans Application. This is better than relying on Building Notices, as it will cover all the necessary safety elements in advance, minimising the likelihood of your project being halted.

Remember that in conservation areas, or if your property is a listed building, there will be much more stringent planning application rules. Check with your Local Planning Authority before doing anything else to find out if you can go through with your job.

What safety advice will I need to follow for a basement conversion?

Ceiling height

If your basement does not have adequate headroom you will need to have the floor lowered. Building regulations do not list a strict minimum for the height of a basement ceiling, but a good target is 2400mm. Remember that if you fail to provide enough headroom it will be easily noticeable, and your expensive conversion will not add value or convenience to your property.

Excavations can sometimes reach ground that has been contaminated with gas. If this is the case the ground will need to be ventilated and the new floor gas proofed with a special membrane in order to protect your property.


A basement conversion requiring significant excavation work, waterproofing and so on can take several months to complete. If your basement does not have external access, tradesmen will be walking to and from your basement carrying tools and waste materials throughout the job. Certain jobs such as replacing a concrete ground floor can make your property unliveable.

Discuss how much of a disruption will be caused by the job whilst you are still in the planning stage. Ask your tradesmen whether you will need to find temporary accommodation and how long for. You should also make sure to ask about how they will dispose of waste materials. If you are eager to save some money with DIY work, getting rid of this material can be a job for you.


What type of tradesmen do I need for a basement conversion?

It is a good idea to speak to a specialist company about your basement conversion. Such companies will have a well established team of specialist tradesmen on hand, which is a big bonus if you have not organised a project like this before. Structural surveyors and builders will be required, but depending on exactly what you are converting your basement into, you could also require an electrician, a carpenter and so on. If your ideal conversion is particularly ambitious, you may even require a specialist designer. A specialist company will also likely have a number of examples that you can look over on their website. 

basementThe main thing that matters is making sure of the background and qualifications of your tradesmen. Even if you choose a 'specialist' company, you should still take the time to look over their workers. They should at least have completed an apprenticeship or equivalent qualification, and may have passed additional industry courses. Check their experience too: have they worked on a lot of projects similar to yours in the past, and were their customers satisfied? The best thing you can do when looking for quotes is to give your potential hires as much information as possible on exactly what you want. They will let you know if they can facilitate your request with the specialists they have, or if you will need to look elsewhere.

Waterproofing is an essential part of converting basements and cellars. Water tables can put a great deal of pressure on your basement, which can cause significant structural problems. To avoid this, ensure that the tradesmen assigned to your waterproofing work are registered with the British Structural Waterproofing Association. Your other tradesmen may also belong to other national organisations. This is a great sign, as such groups enforce high standards on their members.

When planning home improvement work it is important that you can look for tradesmen with the right expertise, and that you get multiple quotes to compare. Doing this can be long and tedious, but Plentific can help you get your search done in no time at all. The Plentific website can quickly create a bespoke contact list of trusted specialists near you with the skills to complete your job. Each Plentific Pro also has a profile displaying their qualifications, experience and customer reviews, making comparing your potential hires simple and easy. The Plentific Guarantee, which can cover your entire project, will also become available if you hire a 'verified' Plentific Pro. Whatever your ideal basement conversion looks like, Plentific is ready to help you find your ideal hire.

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