As part of the Summer 2015 Budget and accompanying report (‘Fixing the Foundations: Creating a More Prosperous Nation’), George Osborne announced that planning permission would no longer be required for upwards extensions of a limited number of storeys in London. This is provided the extension serves to bring a building to the same height as adjoining properties. But what is the future for development in the opposite direction for basement extensions? How far can underground development be pursued without an application for permission? Philippa Plumtree-Varley of Walker Morris’ Planning & Environment team considers the legislation surrounding basement development and the recent ruling in Kensington & Chelsea Royal Borough Council v Secretary of State for Communities and Local Government.

The story so far

With ever-increasing residential property prices in the capital, recent years have seen a substantial rise in the number of basement developments – as homeowners either create new, or enlarge existing, underground space beneath properties. In 2001, there were only 46 applications to ‘dig down’ made to the Royal Borough of Kensington & Chelsea (RBKC). By 2013 this figure had risen to approximately 450. This has generated controversy and concerns. Basements raise issues of noise and disturbance during construction; potential physical and structural damage to neighbouring sites; traffic management; sustainable drainage; carbon emissions; the impact on conservation areas and / or listed buildings; and displacement of ‘traditional’ occupiers from the property market post-construction.

Notable examples of basement development amongst the rich and famous abound. Leonard Blavatnik, reputedly the second richest man in the country, has added a garage, swimming pool, gym and cinema to the space under his three former embassy buildings on Kensington Palace Gardens. A few houses away, permission was granted for an underground tennis court, pool, gym and museum space for a classic-car collection. One South Kensington property has obtained consent for a downward extension to allow creation of a 50-foot pool, gym, cinema and beauty spa.

What does the law say?

The legality of these developments has been somewhat unclear. The Town and Country Planning (General Permitted Development) (England) Order 1995 (the 1995 Order) made no specific provision as to whether or not permitted development rights existed for such works. Similarly no indication has been given in its successor legislation, the Town and Country Planning (General Permitted Development) (England) Order 2015 (the 2015 Order). A number of local planning authorities (LPAs) have regarded basement alterations as falling under Class A works – that is, as permitted development for “the enlargement, improvement or other alteration of a dwellinghouse” and for which a traditional planning application is not required. However, this permitted development right is expressly excluded in both the 1995 Order and 2015 Order where “the enlarged part of the dwellinghouse would have more than one storey and...be within seven metres of any boundary of the curtilage of the dwellinghouse opposite the rear wall of the dwellinghouse”. 

Permitted development rights examined

The recent case of Kensington & Chelsea Royal Borough Council v Secretary of State for Communities and Local Government (17 June 2015, as yet untranscribed) has provided some clarity on the Class A permitted development rights. In this case, in two appeal decisions, the Planning Inspectorate had granted lawful development certificates for single-storey basement developments to existing dwellings at Princes Gate Mews and Colbeck Mews. Despite the additions not extending beyond the existing dwellings’ perimeter, the LPA had objected on the basis of the restrictions in the 1995 Order (noted above). The LPA and Secretary of State (SoS) agreed that the Class A rights apply to both above-ground and below-ground development.  However, the main questions before the court were:

  • whether the “enlarged part” of the dwellinghouse is simply the single-storey basement as argued by the SoS, or if it includes existing storeys in the dwellinghouse as the LPA suggested; and
  • whether the seven-metre restriction was to be measured to the dwellinghouse being developed from any dwellinghouse opposite that, or from the dwellinghouse being developed.

Ultimately, the measurement point was conceded by the SoS. It is therefore now established that the seven-metre restriction is measured from the dwellinghouse being extended. In turn, Patterson J ruled that the “enlarged part” of the dwellinghouse refers solely to the development being added via permitted development rights. So, in this instance, the development only had one storey.

What does this mean in reality?

This is welcome news for those wishing to develop under existing dwellings, indicating that the addition of a single storey falls under permitted development rights provided it complies with the relevant criteria.

However, caution is still required. Where any instance of basement development is concerned, the detail of the proposal is important. It must clearly be within the scope of what is permitted under the Class A rights, otherwise a planning application will usually be required. It is also vital to check relevant local planning policy and note if there are specific restrictions.

What does policy say?

The National Planning Practice Guidance does not provide any specific reference to or assistance for subterranean proposals. Some LPAs have introduced policy restrictions specifically to limit the creation of vertical ‘palaces’. RBKC and Westminster City Council are notable examples. The ability for LPAs to lawfully limit the carrying-out of basement developments via blanket policy has very recently been the subject of a legal challenge in the High Court. However in a judgment issued on 23 July 2015, the Court confirmed RBKC’s adoption of its basement policy (Core Strategy Policy CL7) was lawful. Responding to the decision, Councillor Timothy Coleridge stated: “Our policy brings some much-needed sanity to the mega-basement mania and finds the proper balance between subterranean development and the right of the rest of the community to the peaceful enjoying of their homes”.

In the Policy, RBKC set clear limits to underground developments falling under the normal planning regime. Noting that “a basement development...has an immediacy which can have a serious impact on the quality of life”, Policy CL7 restricts basement excavations as follows:

  • extent – to no more than under half the garden or open part of the site, measured as gross external area; and
  • depth – to a single storey in most cases, with three to four metres floor-to-ceiling height as a guide.

Larger sites and, generally, new developments will be allowed basement works beyond the restrictions. No further subterranean floors can be added:

  • where there is an extant or implemented planning permission for a basement; or
  • where there is one already built as a result of permitted development rights having previously been exercised.

Policy CL7 also outlines specific considerations applicants must address during the preliminary development / application stages, as detailed in RBKC’s Basements Supplementary Planning Document. For example, a draft construction traffic management plan must be submitted with any permission application.

RBKC also intends to impose an Article 4 Direction throughout the borough from 28 April 2016. Directions under Article 4 of the 1995 Order are traditionally used relatively rarely and usually on a restricted scale, rather than borough-wide. However, the Direction will have the effect of removing the existing permitted development rights for basement works altogether. Jonathan Wade, RBKC’s Head of Forward Planning, states that the objective is to “ensure consistency and fairness”and “cut down on neighbours’ concerns about basement developments”. All homeowners will have to obtain full permission for underground proposals and notify neighbours of their plans. Whether any LPA has adequate resources to deal with the increased number of applications likely to result, in a timely and consistent way, is just one of the many concerns this approach raises for owners and developers.

The future

It seems likely that developers and homeowners will need to consider ever-more inventive ways to extend properties, particularly in the capital where floorspace is limited. The changes introduced in the Summer 2015 Budget will be of some assistance here.

Lateral development is increasingly popular. Chris Martin and Gwyneth Paltrow purchased a semi-detached house in Belsize Park for £2.5 million, before obtaining the adjoining property for a reputed £3 million in 2010. After combing the two properties and undertaking some basement excavation, they created a 33-room mansion, joined two gardens and created space for a swimming pool. Roman Abramovich combined nine flats in one block in Lowndes Square, although this was sold before the work was completed. Whether this will be another area in which LPAs introduce restrictions before long remains to be seen. RBKC previously allowed merging of up to four planning units, but since September 2014 all such amalgamations require consent. The policy is apparently to be tightened during the course of 2015.

Vertical and horizontal development remains a viable and effective way for homeowners and developers to expand property, adapting it to their needs and requirements. While the days of ‘iceberg homes’ may be numbered in certain areas, the battle of the basements looks likely to rumble on.