London's latest trend sees home owners digging deep for extra space; we explore the difficulties of basement conversions and extending underground.

Words Nigel Lewis

Basement conversions in London are at an all-time high as homeowners expand their homes rather than move and face a substantial Stamp Duty bill. Despite increased planning restrictions, the number of applications to convert basements has doubled over the past two years which, as builder Billy Heyman of BTL Properties explains, is not surprising.

“It’s a no-brainer, really,” he says. “Our typical customer is living in a £2m house but to move up the ladder locally usually requires a spend of £3.5 plus a Stamp Duty and agent fee bill of nearly £400,000.”

The cost of a basement is much less than that. But getting permission for a basement conversion is getting more difficult as many London borough planning departments crack down on the more ambitious projects. This year Westminster established a ‘sub squad’ team to process complaints about basement conversions, and introduced a tax to be levied on each conversion. This is fast reducing the number of high-profile basement conversions being completed, including those undertaken by Foxtons founder Jon Hunt, composer Andrew Lloyd-Webber, actress Nicole Kidman and oligarch Roman Abramovich, many of whom have added up to four storeys underneath their houses.

“A lot of the councils are tightening up the planning process to try and create as many barriers as possible,” says Simon Haycock of Michaelis Boyd Associates. But the second type of basement conversion continues to boom. These are the one-storey dig-downs that are easy to spot outside a home. Usually, an electric conveyor pokes out of a downstairs window, wet clay clattering from the netherworld below into a skip.

“The really big projects that you see in the papers are all about having a basement swimming pool or cinema, but most of our work is about freeing up space and making a period property a usable family home,” says Simon Haycock.

“Quite often our projects are about moving the utility areas of a house downstairs and therefore freeing up the family areas above.”

If you’re about to take the plunge and go big below, there is plenty to think about. Creating a basement from scratch is a significant engineering project and some experts say it can be more complicated than building a new home.

But if you can get it right and complete your project, then the benefits of a basement conversion are more than just aesthetic. Trevor Abrahamson, of estate agent Glentree, says that while it costs approximately £300 per foot² to build a basement, it can add between £1,000 and £6,000 per foot² to the value of the property, when complete.

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