Design & Build: Edit #5 – BASEMENTS: The Lowdown

Last Updated on : 9th November 2018
Design & Build: Edit #5 - BASEMENTS: The Lowdown

Welcome to our Design & Build: Edit #5 – Basements: The Lowdown

Enjoy the benefit of hindsight before you start your big dig with these insightful tips from NappyValleyNet’s local basement experts. From hidden costs to damp-proofing, how to maximise the space to what to put down there, we’ve got it covered.

While the thought of excavating under your home can be terrifying (how deep, how much, how long?), the literal fear of the unknown doesn’t have to keep you up at night. By turning to a specialist, you can maximise your living space with a well-planned, contemporary addition that will enrich your lives as well as add value to your home. Utility rooms, wine cellars, spare bedrooms, wet rooms, not to mention the storage options – the list of possibilities you can put down there is endless. So if you’re thinking of going underground, read on.

Do I need to have an existing cellar or small basement in order to have a basement conversion?

Contrary to popular belief, no! Believe it or not, an actual basement can be created purely from the ground beneath your home. It is important to choose a basement specialist, which is what we are, to carry out your project due to specialist requirements with underpinning and waterproofing your space.

Simply Basement

How can I integrate my basement in to my house?

It can be difficult to integrate a new basement with the existing house, to ensure it doesn’t become a separate, isolated space. However, with a creative design, new basement spaces can be connected to the house above through atriums and double-height spaces. This creates a dialogue between the new and old parts of the house, ensuring the basement doesn’t feel like a separate addition.

BTL Property

How can I maximise the space?

Think hard about what you want to use the space for. Some people approach basements as a land grab operation – to simply to build the most space possible – but if you haven’t actually thought about what you need the space for, you can end up with a ‘ballroom’ downstairs that never gets used. Many love the idea of a wine room or cellar. It’s a great idea but it does use up a lot of space that could be better lent to, say, a utility room. A good compromise is to have a bespoke wine cupboard or wine wall instead of a dedicated room.

Good London Builders

What are the benefits of going under the garden?

Creating a basement under your garden offers some exciting design opportunities. Overhead light can be achieved through large panels that make the rooms below feel incredibly airy and spacious. Currently, we find the trend

is to extend the existing basement into the garden as far as possible to gain superb quality space without losing any precious garden area.

Advantage Basements

I want to build a basement but I am concerned it will feel damp.

There is no reason why a basement should now be a damp room underneath the rest of the house as long as the waterproofing has been well considered and well designed. In our basement conversions, specialists install a cavity membrane system which works on the principle of allowing water to continue to penetrate the structure but control it in an air gap and then divert it to a suitable drainage point. The advantage of this is that there are no potential weak spots, which can

lead to leaks, stained walls and an odour associated with the cementitious

tanking system.


What are the costs I need to be aware of?

There is a huge price variation quoted for basements ranging from under £2,500 per sqm to over £3,500 per sqm, so check carefully what is included. The answer is complex, but these are the basic things you should check are in the cost estimate/quote:

  • Space planning design
  • All surveys required to support the planning application
  • Planning application fees
  • Detailed architectural and structural engineering and interior design post planning approval
  • Party wall costs (yours and your neighbours’) and movement monitoring throughout construction
  • Thames Water build-over agreement (if required) and drain re-routing
  • Project management of all the on-site building works
  • Insurance backed guarantees, not just the builder’s guarantees
  • Minimum internal finished ceiling height 2.7m and ideally 3.2m
  • Structural waterproofing design and installation fully compliant with BS8102:2009
  • Watertight shell and core construction
  • Glazing and lightwell features
  • Connecting details between the basement and your house
  • Fit out building works and all fixtures and fittings
  • 5%-10% contingency for the “unexpected”
  • And remember, you will need to allocate a furniture budget to fill your new space


We wish you luck with your basement build and if you want any more inspiration, why not get a copy of our Design & Build Guide? Please send me an email with your address to


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