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Lords call for new legislation on basement extensions

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A private member’s bill has been tabled to combat the ‘rapid growth of unregulated’ underground extensions

The Subterranean Development Bill, introduced in the House of Lords last week by Lord Selsdon, calls for better protection for neighbours from underground redevelopment and sets out a proposed code of practice.

In recent years there has been a large hike in the number of ‘iceberg homes’ being built - there have been 700 applications for basement excavations in the London borough of Wandsworth alone in the last three years.

Because planning permission is not needed if the extension is within the footprint of a single-family house, and is less than three metres deep, subterranean expansion is becoming increasingly tempting to homeowners - especially in London.

Disruption to neighbours, as well as concerns over effects on the local environment, have led to increased complaints to local councils, prompting the proposed legislation.

Jim Cook, Buro Happold principal and group director for ground engineering said: ‘More control within the industry regarding the construction of basements is welcome.’

He added: ‘There are a number of issues around the construction of basements under existing dwellings, including disruption to neighbours, damage to properties, health and safety matters, and their effect on local utilities and services.’

Others raised concerns about the imapct on the water table. Michael Coombs, senior partner at Alan Baxter said: ‘There are varying groundwater conditions near the surface in London which are to do with perched water… and the mainly lost rivers which drained London’s rainwater. In many areas these underground flows continue and must be considered when designing new basements.’

While a single basement may not have any effect on the local water flow, problems may be caused by the snowball effect of more landlords opting to build basement extensions.

‘Large basements or a continuous run of basements could cause problems by blocking the flow of underground perched water, leading to raised water levels and problems nearby,’ Coombs said.

‘Isolated local basements will not do this, so the issue is how does one safeguard against a series of isolated basements in the same street which in time join up.’

There are fears that further regulation could discourage building projects and reduce work for the construction industry. “There is a danger that there could be a knee-jerk reaction to this issue,’ Coombs said: ’This could not only adversely affect the workload of architects and engineers but it could affect London’s property market.’

Robert Adam, director of Adam Architecture said: ‘There might be a case for asking for a check on the water table and there should be building regulation approval for construction work.’

But he criticised the proposal, and said: ‘This [Bill] is an incredibly poorly thought out knee-jerk response to ill-informed NIMBYs turned into red tape nightmare – just the sort of thing I thought the Conservative Party was going to stop.’

Adam linked the trend of building basement extensions to the difficulties in the property market. ‘People choose to extend their properties downwards because there is not enough property of the right size. The fact that people are doing it is a secondary issue - the primary issue is the property market and that there is a shortage of housing. As the value of property goes up, people will want to build down.’

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