Building Underground: What could you do with a Basement Building Extension?

If you can not extend outwards or upwards, there is another way, downwards. Use the ground beneath your house to gain that valuable extra space. Refresh UK can assist you in getting planning permission, meeting building regulations and understanding the type of soil you're excavating.

undergound renovations uk

Do you need extra space, but aren’t in a position (or don’t want) to move house? If you can’t extend outwards or upwards, there is another way. You could consider a basement building extension or basement conversion, using the ground beneath your house to gain that valuable extra space.
Simon Kelliher from Refresh Renovations says, “With house prices as they are, extending or converting a basement is now becoming a viable option for those needing a bigger home. The space created can be fantastic and modern glazing options can really bring in loads of natural light.”

Why you should consider a basement building extension

Basement building extensions are becoming increasingly popular in the U.K. for several reasons. The prohibitive cost of climbing the housing ladder, along with stamp duty rates, estate agency fees, and conveyancing costs mean that extending an existing property is an appealing option for those looking for extra space. It’s often possible to add the cost of an extension on to your mortgage, especially if you have a good amount of equity in your property.
A basement building extension also adds value to your house, making it a great opportunity for homeowners and investors alike.
undergound house built in UK
It’s not uncommon for older houses to have basements that are relatively unused and ripe for renovation. As Simon says, renovating a basement like this, “can be relatively cheap when compared with an extension, and does not need to impact the size of your garden and outdoor space.”

What can a basement building extension be used for?

Well, the limit is really your imagination (and budget!). From a practical point of view, basement building extensions and basement conversions are great for playrooms, living and dining areas, and kitchens. If you work from home, a basement office provides much-needed quiet. For a growing young family, basement bedrooms will give you the space you need. With grown-up children increasingly living at home for longer, or older relatives to take care of, a basement building extension could also be used as a granny flat or bedrooms, a living room and bathroom for teenagers.
Luxurious bathroom built underground
If you’re looking for extra space to accommodate a luxurious lifestyle rather than your in-laws, basement building extensions can be put to epic use. Think home gyms, swimming pools, saunas and hot tubs. You can entertain friends in your personal cinema room, games room or bowling alley, before sampling the best vintages from your wine cellar.  
If you have a number of cars, expensive models which need to be secure, or simply have difficulty finding a parking space, this can be solved with a basement garage. Options here include a car lift, which will take your car down to basement level; and pivoting car platforms, which turn your car on a turntable.

The pros and cons of building a basement extension

As with any building work, building a basement extension or converting an existing basement has its pros and cons.
UK undergound house


  • Basements are a great option if you can’t extend out into your garden or up into your loft.
  • Contrary to what you may think, it’s possible to flood basements with natural light by using borrowed light. This can come from external light wells, sun tunnels, double height spaces and glazed floors.
  • As well as providing borrowed light, you can also create a courtyard garden, and have glass doors opening onto it.
  • Basements are a great option to build rooms which don’t need natural light – cinemas, wine cellars, utility rooms, garages and bathrooms, for example.
  • If you have an existing basement, even if it needs work or has a low ceiling, it is cheaper to convert it than it would be to build an extension to your house. ### Cons:
  • Let’s be realistic, the cost of building a basement extension can be high. However, if you live in an area where you can’t build outwards or upwards and house prices are high, basements can actually be the financially viable option.
  • The building process for either a basement conversion or extension is difficult, messy, loud, and disruptive (not unlike any building work). ### Which type of basement extension is right for you? There are three ways of building a basement extension:
  • Conversion or refurbishment of an existing basement – a straightforward option.
  • Adding a basement an existing property – requires extensive excavation. A good option for when there’s no other way to gain extra space.
  • Building a new basement as part of a new house build – another straightforward option and a fantastic way of making the most of the land you have to build on. building in uk ### Technical considerations when building a basement extension There are a number of technical considerations when building or converting a basement. Primarily, this includes getting planning permission, meeting building regulations and understanding the type of soil you’re excavating. Once these necessities are in order, you need to consider natural light, ventilation, circulation, and waterproofing. underground renovations Andy Aitken from DK-Architects says, “Key issues are waterproofing and structural stability both of the basement itself but critically also of the existing property above. It’s essential to involve specialists in the design of your basement as they will ensure the success of your project.” Simon agrees, saying, “Digging out a new basement under a house can be a tricky affair. We would recommend using companies that have done basements before as the risks involved are very high, especially in terraced housing where it’s not just your house that is at risk.” You might be interested in reading this case study of Refresh: Going Under – A Home Excavation. ### Get in touch with Refresh to discuss your home renovation project If you would like to discuss home renovation options for your next renovation project, please use the enquiry form on this page to provide us with your contact details. We will get in touch with you at a time that suits you to discuss your project. If you would like to provide us with more information about your project, we have a more comprehensive enquiry form on our "Get in touch" page too.
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