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Should one enlarge ones home by digging?

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Knight Frank
London and Country specialist property buying agents
19 Jul 2017  |   Philip Eastwood

With the costs of moving so high, and the ability to build another floor on a house limited by strict regulations from many central London councils, when clients want to have more space, they will often consider digging out a basement.

Just a few years ago, London’s streets were covered with excavation works digging out larger and deeper basements. Since then, councils have stepped in to introduce tighter measures. Today, it’s more challenging and expensive to gain planning permission for a basement than it once was but it’s by no means impossible.

When clients ask me to recommend an architect, I often turn to Hodgkinson Design. The west London-based practice has an excellent track record of residential projects and is headed up with the multi-disciplinary award-winning designer, Andrew Hodgkinson.

Chartered architect Chris Pring of Hodgkinson Design has a great deal of experience working on listed buildings and on projects within conservation areas and covenanted private estates such as the Phillimore Estate, Grosvenor Estate, Bedford Estate and Hampstead Garden Suburb Trust. Here he explains the process of building a basement in London.

“Basements are a good option for someone looking for extra space but it’s fundamentally important is to get the right professional team in place before starting otherwise you could end up making some expensive mistakes.

The main reason that they’ve become so popular is because it’s more and more difficult to secure planning permission to add an extra floor to a house—particularly in central boroughs such as RBKC (Royal Borough of Kensington and Chelsea) and Westminster. Even if there is a precedent in the street already and even if you can’t see the floor from the street level, this doesn’t always lead to permission being granted; a basement, in contrast, is more simple.

Up until recently, the building of basements in London fell within Permitted Development and were an easy way to gain that extra space, albeit at a cost. However, in the last few years, in response to protests against so-called ‘iceberg’ basements (multi-storey basements), that has changed.

Today, you need to provide a full basement impact assessment before you submit your planning permission which involves going to the expense of instructing a structural engineer. Once planning is secured in principal, you have to seek party wall agreements–in itself this can be challenging especially if the property adjoins a house or building containing multiple flats as each of the owners needs to sign a party wall accord–and get building control involved. Planning permission for basements involves a large financial outlay which only the very serious will be prepared to undertake.

As a rule of thumb, basements cost between £200 and £300 per sq ft to build the box—where costs go from there depends entirely on the client and what they have in mind. The largest basement that we’ve done is 3,500 sq ft in north London which went under the footprint of the house itself as well as part of the large garden. We built a pool of 10m x 5m, a cinema room, party room, gym and sauna area.  We’ve also done more modest ones which give the owners space for a gym or cinema room, pool or games’ rooms. If you can get natural light and ventilation into the basement, then it’s possible to make the space into extra bedrooms and living rooms.

They are quite complicated projects and require a lot of thought but are a good solution for those needing extra space. A well-designed basement won’t feel like a basement—it’ll feel just like another room in the house.”

Basements can add value but it is important that the basement extension benefits from natural light. The key to a good basement extension is that the extra rooms are desirable rather than just increasing the square footage. The Buying Solution will often consult with clients post purchase on these matters providing comfort that their proposed plans are sensible.

Hodgkinson Design (020 7221 7557;

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