Architects FAQs on basements

We are the leading basement experts in the South East and London (and probably the country, if we’re being honest). This means that we are the first port of call for many of our colleagues in the general architectural sector for advice when they pick up basement projects; quite often we end up doing the work on their behalf.

Whether you’re designing a retrofit basement for the first time or planning for your 100th project, there’s plenty to think about. After all, when it comes to subterranean architecture and design each space is as unique as the building under which it is going.

Luckily, we’re experts and walk our clients through every step. The questions we get from homeowners about basements tend to differ from those we get from our colleagues in the construction and design industry, so we have compiled a few of the most common.

If you would like to speak to a member of our team about your basement options, give us a call on 01628 826066 or email us.

Can I retrofit a basement?

If you have the plot and the footprint, almost anything is possible. Obviously, the project needs to be feasible and financially worthwhile to the homeowner. You wouldn’t dig an underground gym and swimming pool for a two-bedroom terraced home in the north of England where property value would be less than the cost of the works.

The best option when planning a retrofit basement is always to consult with an experienced specialist. There are many considerations that go into this type of project, including ground level and soil types in order for it be successful; although there may also be certain limitations depending on the existing structure which would need addressing before starting anything.

How much does a retrofit basement cost?

The cost of a new basement in London can vary greatly depending on what you want. The average price for digging out the necessary space and finishing it off with drywall is about £4,500-£5,500 per square metre but this number will change based upon variables such as materials used to build your home’s structure- from concrete block walls all the way up towards expensive stone finishes or other complexities that may be required if the property is listed.

Can I dig externally?

Yes, you can. The term ‘digging externally’ refers to when you are building a subterranean space outside the footprint of the existing building. In this instance keeping the structure stable and secure with pile positioning is vital, combining this with a solid soil retaining solution will ensure that the project is undertaken safely.

Waterproofing and the pumping systems are one of the most important aspects of basement excavation. Digging a retrofit basement doesn’t necessarily affect the water table but it is more important for you to have a solution that redirects the flow of water in order to keep your basement dry and free of damp.

How to use piles in basement excavation

The number of piles you will need depends on where the basement will be. If you are digging outside the footprint of your home then more piles will be essential for supporting the retaining walls.

However, if you are building directly under an existing structure you will need to underpin as you go in order to strengthen and secure the foundation of the building; this should be calculated by a structural engineer and distributed at critical load points.


Water damage is devastating and for that reason ensuring adequate waterproofing is one of the most important elements in the basement industry. The most common and reliable technique of basement waterproofing is the installation of cavity drainage systems to the external perimeter basement walls & floors.

Our experience tells us that it is almost impossible to stop the ingress of water in the long-term, therefore we allow the water to flow naturally into sump pumps which then discharge automatically to the existing external drainage system as and when required leaving the internal spaces completely dry.

Common planning issues

Planning permission can be a fairly major hurdle to get over – we have often spoken about planning issues in our previous blogs and, while there are hundreds of things that can delay a project, more often than not it’s the planning permission stage. Even though there has been talk of reform in the planning application process, there are still a number of other permissions which need to be granted before ground can be broken.

Get in Touch

If you are thinking about undertaking a basement project, extending your property, or you are an architect who needs some help with a basement project make sure you give us a call. We are the leading specialists in basement conversions and design. You can call us on 01628 826066 or email us. You can also follow us on Facebook, Twitter, Instagram, and LinkedIn for all the latest updates.

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