A High Court ruling this month suggests that excavating a new basement may not count as "permitted development". This could have a much wider effect on town planning beyond the domestic.
Background – the basement trend
Where space is scarce, basement extensions have become popular, with press accounts of "iceberg" basements extending beneath rear gardens. But this month's decision in Eatherley v London Borough of Camden was not about these. It was about a small, windowless basement restricted to the footprint of an existing terraced house in Camden.
Did this basement need a specific planning permission? The owner of the house, Mr Ireland, thought not, and the local authority agreed. But a number of neighbours led by a Mr Eatherley argued that the work could not go ahead without a specific planning application.
What is "permitted development"?
Most building operations or changes of use are treated by law as "development" for which planning permission is needed. However, the General Permitted Development (England) Order or "GPDO" grants automatic permission to certain types of development, so that a specific planning application is not required.
Class A of the GPDO permits a category of development defined as "the enlargement, improvement or other alteration of a dwellinghouse". This is subject to conditions, e.g. the ground covered by the building must not be increased by more than 50% and the height must not be increased. Class A is often used for conservatories and minor rear extensions.
Mr Ireland proposed to excavate a new basement under his house. He applied for a certificate that this would be "permitted development" under class A. The council granted the certificate, but this was challenged by Mr Eatherley.
The High Court's decision
Mr Justice Cranston said it was crucial to consider the excavation, underpinning and support needed to construct the basement. In his view, class A of the GPDO permits alterations to buildings but does not necessarily permit the engineering works required for those alterations. In his words:
"There must be a point where the excavation, underpinning and support for a basement for a dwellinghouse becomes an activity different in character from the enlargement, improvement and alteration of that dwellinghouse… The development of a new basement, when there is nothing underneath at present, could well amount… to two activities, each of substance.
"There is the enlargement, improvement and alteration aspect, but there is potentially also an engineering aspect of excavating a space and supporting the house and its neighbours... Class A grants planning permission for one of the two activities… but not for the engineering aspect."
The judge said the council should have considered whether the engineering works amounted to "a separate activity of substance", distinct from the basement itself and not covered by class A. The council's planning committee had not asked itself this question, and therefore the certificate should be quashed.
The judge's decision is a setback for homeowners wishing to build some smaller basements, but may be welcomed by some of their neighbours. Without permitted development rights, an application will be needed, triggering the full range of consultation, planning polices and controls.
The case is unclear on the test to be applied as to when engineering works become separate and, more crucially, cease to benefit from permitted development rights. If the judgment stands, it will lead to difficult decisions for other residential and indeed non-residential alterations. Can a single-storey above-ground extension still rely on class A permitted development rights, if the extension needs new foundations? Will any works involving piling count as a separate engineering development for which specific planning application will be required?
The Camden decision may only have involved a small house in Kentish Town, but it could shake planning law to its foundations.