Home extensions and renovations Converting or creating a basement
It can be simple and cost effective to convert a basement
If you already have a basement, then converting it to a useable room is a fairly simple and cost-effective procedure. If, however, you are creating a basement from scratch, the work will take a lot of time, be very disruptive and cost an enormous amount of money in comparison with other ways of creating extra space.
As a result, if you are thinking about creating a new basement, and one doesn’t currently exist, check first the feasibility and costs of creating the space you need elsewhere and only go down this route if it is absolutely what you want or there is little other choice.
Converting a basement
In most cases, you won’t require planning to convert an existing basement. Contact your local planning office in writing so they can confirm formally that you can go ahead with the work – it’s useful to have proof that planning wasn’t needed if you sell your property.
The key to a successful basement conversion is that it's waterproof. To do this, you need to ensure that the basement is well ventilated. You must also adhere strictly to the building regulations – especially to make sure that the area is structurally sound. Only a qualified and experienced surveyor can do this for you.
Ideally, your basement will also be 2.4m or more high – the standard tends to be around 2.7m high. There aren’t any limits on width as long as it’s within your boundary.
Creating a new basement
Creating a basement is an enormous task, that costs a lot of money.
The key consideration is the type of land that your home is sitting on. If there is a high water table that may cause flooding, the cost of preventing this from happening may be out of your reach. If mains drainage runs underneath your house, it would be an enormous task to try to re-route it. It is likely, too, that this would cause problems not just for you but your neighbours, whose pipes may be affected.
Once you have checked these factors out, ensure the foundations are either good enough to cope with the excavation, or that they can be underpinned for safety’s sake. If you are in a terraced property, this is particularly important to understand as you will need a Party Wall Agreement to planning permission/party wall section with your neighbours.
Key questions to ask if you're converting a basement
How will the basement be lit?
If it is impossible to get any natural light in, you may want to have a dark room, cinema room or space for parties. If, however, you are looking to create a kitchen, extra sitting room or a study, you need to think very carefully about whether you can live without natural light.
Choose a reputable contractor – even if it costs you more
If you can’t, then a small extension out into the garden area may allow you to add light pipes. These are cylindrical devices put in the ground that use reflective surfaces to pipe light into the room downstairs.
Another option is a window well, which is a double-glazed window that lays flat on the ground and passes light through to the basement. The key benefit of a window well is that it can also improve ventilation.
How will you heat your basement?
Ideally, get the cleanest, safest form of heating to help keep you warm. This will invariably be electricity, as any gas services require a flue to discharge emissions. As with loft conversions, it may be best to create a separate ring main for the electricity so you don’t overload your existing system.
How will you damp proof the basement?
When you come to damp-proof your basement, there are two main methods – make sure that you choose the best for your project.
Cement-based system This stops any water from entering your basement. It sets a bond with the masonry substrate, creating an impervious barrier.
Water membrane system A membrane is sealed to the walls, ceiling and floor and then covered with plasterboard, screed or a floating timber floor. This system allows water to drain away, often with the help of a pump and drainage channel.This is particularly suited to waterproofing old Victorian basements.
Choosing a contractor
There is a massive benefit to getting a reputable company in – even if it costs you more – as you will get good guarantees with their work, for 10 years or more. This is worth having as a basement that goes wrong will cost a lot to put right.
Look for companies that are recommended by the Basement Information Centre which runs Accredited Contractor Schemes, and the Federation of Master Builders
For underpinning and water-proofing or damp-proofing, there are organisations such as the Association of Specialist Underpinning Contractors and the Structural Waterproofing Group.