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DIG DEEP - Can I go underground with an extension?

DIG DEEP - Can I go underground with an extension?

Running out of space? Kids getting bigger? No more room to extend up or out – what about extending underground?

Underground Extension

In recent years, more and more homeowners have turned to subterranean extensions as a way of retaining garden space yet also providing additional rooms.

But it comes at a price and is usually only spotted in the rich enclaves of famous footballers, Russian millionaires and in certain high-end roads in London. Excavating the ground under your home to create a basement involves major works, high costs and may well require planning permission.

The good news is that the vast majority of local authorities will let you dig deep under planning rules known as Permitted Development Rights. However, there are limits to how deep you can dig and how far out.

In 2016, a High Court case clarified the rules to say you can extend your house under permitted development rights by adding a basement, as long as it is only one-storey and extend no more than three metres from the back wall of your house (and leave seven metres between the end of your basement and the boundary of the neighbour opposite). Anything more will require full or specific planning permission.

Two-storey basements or ‘Iceberg’ homes (where the basement space underground is significantly more than the house that appears on the surface) are generally not allowed, although the London Borough of Kensington and Chelsea did approve one at the Oman Embassy in London in 2015.

You also have to consider whether your plot or property is even suitable for a basement. Some situations might mean digging deep is not a viable option, for example if you have;

  • High Water Table
  • Unsuitable bedrock
  • Existing structures and services
  • Archaeological finds

Ultimately, if well designed and executed, basements can create new and amazing spaces for growing or multi-generational families. Basement conversions can be used as bedrooms, games rooms or wine cellars and can often present a workable solution for people wanting more room without eating into their garden space.