Shilpa Mathuradas: Insider Tips For A Smooth Basement Development

Although basement excavations are expensive and fraught with logistical difficulties, in Central London and its suburbs extension of a home’s square footage in a downwards direction can increase its value by up to 15%.

Newly developed basements in the London homes of the super-rich have become a status symbol and a way to increase returns on property investment. These homes, known to many as ‘iceberg houses’ due to the fact that most of the living space is under the surface, boast glamourous features such as swimming pools, gyms, multi-car garages and wine cellars.

Here are some important factors to consider when completing your (or your clients) basement conversion:

Neighbours Objections

Firstly, it’s important to note that it can take up to two years to excavate and construct basements on this luxurious scale.

Unfortunately for long-suffering neighbours, the disruption caused by such work can be significant. Take for example the recent story reported in Camden New Journal, in which BBC weatherman Stav Danous officially objected to a new excavation proposal for a house close to his own home in Swiss Cottage.

The area has already experienced several of these major basement excavation projects, and Danous has had enough of the intrusive site traffic and inconvenience, ‘”There have been three excavations on my side of the road…resulting in continuous disturbance and disruption…the amount of noise…is completely unacceptable.”

In some cases however, disruption of peace and routine is a minor issue when compared to the concurrent damage caused to the foundations of neighbouring homes, damage which can result in significant subsidence and cracking.

Another frequent complaint from neighbours is that most of the house owners who commission these extensive and intrusive works are absent from their London home for most of the year.


“Typically when basement development planning permission is granted to one property, other property owners in the area also apply for and receive permission for similar builds”

Basement Developments 101

If you are considering a basement conversion for your development or your own home, there are a number of practical considerations that must be taken into account:

  • Does the location of the prospective site have sufficient access for work machinery such as JCB diggers?
  • What is the state of the building’s current foundations? Can they withstand the work without suffering subsidence? Will underpinning be required?
  • If there is a high water table or mains services running underneath your building, this could prove tricky and expensive to overcome. In London, the main underground material is clay, which doesn’t permit water flow. For this reason there is a risk that any excavation may expose the build to the upper aquifer. Consequently, it is likely that a pump will need to be fitted in order to keep the basement dry.
  • Like any build, unforeseen circumstances could put your initial budget in jeopardy. Basement excavations take much longer than similar sized, above ground extensions.

Legal Aspects

There will also be important legal issues to consider.

As well as obtaining planning permission for the proposed development, building regulations approval will be required.

As many readers of DMZ will already know, consideration will also need to be given to obligations under the Party Wall Act 1996.

Planning Precedent

Over the past decade, thousands of homes within London have been granted planning permission for basement excavation.

What is more, there continues to be a surge in growth of the basement excavation industry within the city. There is a clear pattern: when basement development planning permission is granted to one property, other property owners in the area also apply for and receive permission for similar builds.

Due to increasingly vocal concerns from disgruntled neighbours, some local authorities in London have reworked their planning regulations to take into consideration the rise in demand for this type of construction.

Even so, I cannot see an end to the popularity of basement conversions in London, not only for the super-rich but for more modest earning households too.


Shilpa Mathuradas is an experienced property litigator for Osbornes Law, specialising in all aspects of residential and commercial property disputes including freeholder/leaseholder disputes, rent review disputes and property related professional negligence.