When to dig deep to build your investment

Posted by Sara Hanrahan on
For the rich and famous of London they have become de rigueur.

It was obvious really – when you can’t go up any higher and there’s no room to extend sideways, then the only option is to dig down.

Largely confined to the wealthier areas of London, ‘mega basements’ or ‘iceberg’ homes have become increasingly popular as owners try to increase their living space and investment value without infringing on strict planning controls.

What started as single storey conversions have quickly developed into two even three-storey basements providing space for indoor pools, private cinemas and living quarters for staff.

Some fear the trend has become out of control, causing years of disruption to neighbours with major engineering works. So much so that a new draft by-law – the controversial draft Core Strategy Policy CL7 – has been developed to give local authorities a way to keep them in check.

Some London boroughs, including the Royal Borough of Kensington and Chelsea (RBKC), are already introducing the policy.

Blake Morgan Partner Sara Hanrahan, who specialises in urban redevelopment, explains the effect that the controversial policy will have on people wishing to extend their homes and where there may be mitigating circumstances.

“Policy CL7 (b) makes it clear that basement development ‘must not comprise more than one storey’ and should be applied to all new basement development,” she says.

 “It is recognised that although basements are a useful way to add extra accommodation to homes there are concerns on the impact on the quality of life of neighbours.

 “As a result RBKC has already decided to rule out the development of double basements, however with the right advice there may well be extenuating circumstances and there are boroughs who are judging each application on a case by case basis.

“In restricting the size of basements the Council seeks to ‘protect residential living conditions in the Borough by limiting the extent and duration of construction and by reducing the volume of soil to be excavated’.  

“However, there is an exception for ‘large sites’ (more than one storey and greater than half the garden or open part of the site) which may be permitted in certain circumstances.   

“We accordingly anticipate a number of applications for double basements to proceed in reliance on this exemption but great care will be required to fall precisely within the permitted circumstances.”

Top 10 tips

  1. Policy position - Research what current local policies are in place for basement builds and whether there are any restrictions; if restrictions are in place see if any exemptions may apply and beware that large basements may trigger an affordable housing contribution so check the thresholds
  2. Team - Make sure the team assembled to carry out the works are all properly qualified
  3. Party Walls - If the works are likely to affect party walls employ a specialist party wall surveyor
  4.  Application - It is strongly advisable to submit a pre-application enquiry first to check that there will be no problems with a full application and so avoid a potential refusal
  5. Neighbours - It is recommended that you discuss any plans with neighbours before submission to see if the design can accommodate any concerns eg minimise light wells to avoid light pollution
  6. Construction Method Statement - Generally some sort of statement addressing ground conditions and ways to minimise disturbance will be required with an application
  7. Traffic report - A draft report looking at traffic flow and highway safety will need to be commissioned
  8. Listed building - If the property is listed extra care will be needed to address heritage issues. Employing a heritage expert is useful
  9. Flooding - Flooding is always an inherent problem with basements so a suitable pump will be required
  10. Trees - If the proposed works could affect existing trees a full survey should be obtained from an arboricultural specialist



About the Author

Sara specialises in urban redevelopment projects, particularly advising in relation to compulsory purchase and affordable housing schemes.

Sara Hanrahan
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020 7814 5407

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