A guide to converting your basement space

It seems that as a nation, the UK has taken to heart the suggestion “don’t move, improve”.

With stamp duty hikes and property prices creeping ever higher, growing numbers of homeowners have decided to dig deep, not just into their bank accounts but into their basements to create extra space.

While the multi-million pound mega-basements hit the headlines creating ‘iceberg’ homes (bigger below than above), most Brits are aiming for something more modest like a basement kitchen, playroom, laundry or bedroom. Some houses – particularly Victorian and Georgian terraces – have full basement suites of rooms already in place that, if not already in use, can be converted into standalone basement flats.

Simple cellar conversions

A basement or cellar conversion can be as complicated or straightforward as you want to make it, but depends on the space you already have available, how much disruption you can put up with, and how much you want to spend.

If you have an existing room below and just want to make it habitable, you just have to take a few steps to make sure that the damp stays out and that there is proper access. This might only take a few weeks and involve adding a membrane lining (also called tanking), digging out the sump and adding in a staircase.

Just improving the existing space may limit what it can be used for – ceilings may be low and there is unlikely to be any natural light. With no windows, you will also have to consider that in an emergency, the only way in and out will be by a single staircase. Tanked walls also mean you can’t fix anything to them, not even carpet tacks. All furniture, pictures and lighting will have to hang from the ceiling or be free-standing.

You won’t need planning permission if you’re not digging out any new space but you will need building regulations approval if the space wasn’t already liveable in before you owned the house. This will check the safety of the basement’s construction and any new additions you make to it. 

Structural basement conversions

Expanding the space in cellar conversions is a bit more involved. You could be digging down to create more headroom, or sideways to make more space or rooms. You may even extend into the garden so you can fit windows and gain access to the outdoors.

In all these cases you will need architect’s plans, planning applications and possibly even party wall agreements if the work you’re doing affects your boundary with next door, even below ground.

Excavating underground is also around twice as expensive as creating the same amount of space in a loft so you should work out beforehand why it’s better to go down rather than up. Will it add the same amount of value to your house? Basement buildings only generally add value if they have plenty of ceiling space and natural light.

When you start tampering with a previously unused underground part of your house, it’s essential that you get the right surveys done and make sure that everyone involved, including you, is properly insured.

The basement is part of the foundation where the whole rest of your house sits and if something goes wrong, it can have a catastrophic impact on the rest of your home. Fortunately, disasters are rare but you want to make very sure you’re looked after if something does happen.

Basement flats

Creating a basement apartment adds a whole new interesting dimension because it brings another asset to your house. If you can create a self-contained flat with its own access underneath your own home, you can either use it as a granny flat for your own family or create income by letting it out.

Again, you will require planning permission and building regulations whatever you decide to do because even if you don’t do anything structural to it, you are almost certainly changing its use, which involves the council. It’s even more complicated if you’re in a conservation area or your home is listed.

If you are going to let it out once you’ve finished, you need to think about the typical landlord requirements such as gas and appliance safety, and fire doors if necessary. If the basement flat has its own entrance, then your tenant will be on a different type of rental agreement than if they come through your house to get to their rooms. Check out our information for landlords to find out more.

The final thing to consider when converting a basement into a flat is the maths. How much is it going to add to the value of your home compared to how much it will cost to do? Will it add value at all (some people don’t like the idea that strangers could live in the floor below them)? Are there other properties like this in the area? When you come to put it on the market, could you even sell both house and flat separately? Would that make it a good investment? What would you need to include while converting to make this possible?

It may seem like there are lots of questions to ask when converting your basement. Try to think of everything before you start and look for advice in as many places as possible. Then you stand a chance of creating somewhere great to live and possibly making a bit of money from it too!

Find out more about Home Insurance from MORE TH>N.

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