Teal blue graphic

Digging deep to extend - what planning issues may arise?

Carrying out an extension has always been a cost effective way of obtaining a larger property without the trouble and excessive costs involved in moving house. Whilst adding an extension to the rear or side of a property may be an easy solution in rural or suburban areas, it is not a viable option in inner city locations, where land is scarce. Subterranean extensions have thus become more common in London and other cities.

Below we set out below whether your basement extension would need planning permission or may be treated as permitted development. 

If a type of development has the benefit of permitted development rights, that development is, in effect, granted planning permission without the necessity of applying for it. Whilst there is no specific provision for basement extensions in the Town and Country Planning (General Permitted Development) (England) Order 2015 (the Permitted Development Order) (or the previous versions of this), most local planning authorities have treated basement developments as permitted development. Therefore, there has been no need to obtain planning permission. This has often caused a degree of dissatisfaction amongst local people who do not agree with, what can be, large extensions going ahead without the opportunity for interested parties to voice their views.

Under the Permitted Development Order, the enlargement, improvement or other alteration of a house is permitted, subject to certain qualifications. One of these is that the enlarged part of the house would have more than a single storey and would extend beyond the rear wall of the original house by more than three metres or be within seven metres of any boundary opposite the rear wall of the house.

The London Borough of Kensington & Chelsea recently sought to clarify whether this restriction meant that the addition of a floor below ground level brought underground extensions outside the permitted development regime. The council's view was that adding a basement added a storey and, therefore, the enlarged part of the house would have more than a single storey. This interpretation was rejected by the High Court. Whilst adding a basement adds a floor to the entire property, the "enlarged part" of the house did not consist of more than a single storey.

The case takes a common sense view of the interpretation of the Permitted Development Order in relation to residential extensions, and clarifies the meaning of "enlarged part" in relation to both extensions carried out under, and above, ground level. It will come as a relief to homeowners who intend to carry out extensions. However, anyone intending to carry out an extension to their home should be aware that there are other qualifications to the right to use permitted development rights. For example, properties in conservation areas are subject to more stringent controls.If your property is listed, although planning permission may not be required for an underground extension, it is highly likely that listed building consent will be needed. 

The London Borough of Kensington & Chelsea has sought to curb future basement extensions by the use of permitted development rights by adopting a Basement Planning Policy as part of its core strategy. This places more stringent controls on basement developments. However, as permitted development rights can be used to carry out such extensions, the core strategy is, in most cases, superfluous. A challenge to the policy on basement developments, in which it is argued that the policy was adopted without due regard to the effects on permitted development rights and is "fundamentally flawed", is currently before the High Court.

The only effective route for local planning authorities to prevent development that would otherwise be permitted under the Permitted Development Order is by the use of an Article 4 direction. An Article 4 direction effectively withdraws permitted development rights and means that an application for planning permission has to be made.

Given the conditions that have to be met, the various policies that may exist, and the possibility of an Article 4 direction being in place, advice should always be sought from a qualified planning lawyer before embarking on any subterranean development works.

Contributor: Alexandra Holsgrove Jones

This publication is intended for general guidance and represents our understanding of the relevant law and practice as at June 2015. Specific advice should be sought for specific cases. For more information see our terms & conditions on www.TLTsolicitors.com

Insights & events View all