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Important Considerations for Basements

Date: 02/06/05
Water level
An important element of the decision as to whether to progress with a basement conversion is the height of the water table around your house.
Steve Bushell suggests digging a test hole up to 2 metres below where you want your foundations to stop, to test the water level. It’s also worth talking to the local water board. “You can tank and damp proof your basement, but if your water table is too high, the costs may be prohibitive,” Steve adds.

Planning permissions:
You don’t usually need planning permission for a cellar conversion unless you significantly alter its usage or add a light well, which will change the external appearance of the property. You will however need planning permission to create a new basement. It is always worth checking with the local authorities in all cases to make sure you comply with Planning Permissions.

Party wall agreements:
Your neighbours will worry about the possibility of subsidence when you begin work on your basement, so it is important to draw up Party Wall agreements with your neighbours, before you start interfering with their walls and foundations. Under the Party Wall Act, they are entitled to the services of a surveyor to look after their interests at your expense.

Building regulations:
Structural work needs Building Regulations approval. This can also apply to electrical wiring, safe access, a fire escape route, ventilation and damp proofing.

If the basement is correctly tanked and damp proofed and well ventilated, then there should be no problems. However it’s worth remembering that a basement will have no direct sunlight so will be naturally cooler and require more heating.

In terms of Building Regulations, if you have an open staircase into the basement, this is deemed to be adequate ventilation. However if the basement has doors separating it from the stairs or it houses a bathroom, bedroom or kitchen, then Building Regulations would require a natural airflow, for example through an air pipe from outside.

There will be little natural light coming into the basement area, so it is important to consider how you want to light the downstairs area. It is possible to dig out from the front or back garden and use paving lights to bring the natural light into the basement. You can also position the staircase to bring natural light downstairs.

Basements do cost more than loft conversion or extensions, because of the effort involved in digging down to the foundations. Where you have to start from scratch, the costs will be around 60% greater than for converting an existing cellar or basement.

Steve Bushell added: “As with all building projects, it is important not to underestimate the costs. When you have calculated your budget, we recommend that you add a 10% contingency to allow for the unexpected and to reduce the consequent stress.” said Steve. (
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