How iceberg basements have changed planning
Digging deep: excavation under way on a basement project in Hampstead, London
The subterranean building boom has required a change in approach from local authority planning officers. Salvatore Amico explains.
In today’s modern cities space is at a premium, which is why the extending of residential properties has become the norm.
While many look to add structures to the back or front of a property or consider a loft conversion, there is a growing trend for the construction or conversion of basements. In fact, recent research shows that in the last decade the number of planning applications in the UK for the addition of basements to an existing home has soared by more than 183%.
London and its upscale areas, such as Kensington and Chelsea, have seen some of the largest growth in basement developments, with the top 16 local authorities for basement planning applications all within the capital.
Due to this sudden surge in interest, the planning regime has had to constantly evolve, as councils and the courts draw different interpretations for current legislation.
While conversion of an existing basement into a living space is not likely to require planning permission, problems arise where homeowners go further and instead excavate under their homes and gardens in order to build new basements or extend existing ones.
This requires substantial engineering work and can cause significant disruption to neighbours, as well as putting their properties at risk from damage, which is why it will usually require a planning application or at least discussion with local planning authorities.
In the past, most councils allowed for the creation of new basement space under permitted development rights. However, since the decision in Eatherley v London Borough of Camden in 2016 – which centred on whether engineering works were a necessary part of the basement development or a separate activity – most councils have made it compulsory to submit a planning application when extending a basement.
“While conversion of an existing basement into a living space is not likely to require planning permission, problems arise where homeowners go further and instead excavate under their homes and gardens in order to build new basements or extend existing ones.”
In this case the claimant, Michael Eatherley, challenged the decision by Camden Council to grant a certificate of lawful development for a single-storey basement extension under the permitted development rules.
He argued that Camden Council had confused itself by believing that the engineering operations were “necessary” for the basement development to occur and would automatically fall within the scope of Class A of the General Permitted Development Order (GPDO).
The judge in the case found this approach to be inconsistent with case law, which stated that an activity could be a “separate activity of substance” even if necessary for, and integral to, the development authorised under the GPDO. This means that most basement developments do not in fact fall under permitted development rights, as previously thought, but should instead require planning permission.
This is not to say that all builds will need permission, but it does mean that most local authorities now require permission to be granted before work can go ahead.
More on basements
- London planners step up campaign against iceberg basement ‘epidemic’
- London council to introduce basement tax
- CPD: Waterproofing below-ground structures
Where permission is definitely required in all cases is where the basement exceeds more than one storey. This comes after the High Court clarified planning legislation by ruling that a person can extend their house under permitted development rights by adding a basement, as long as it is only one storey.
Additionally, a subterranean development cannot extend beyond the boundaries of the property in to another property owner’s land, with or without permission.
Most local councils will also stipulate that you can’t excavate a basement more than three metres beyond the back wall of a house. This is true whether the build requires permission or not, apart from in a few exceptional cases.
Policy on the creation of new living spaces within basements is constantly changing and is full of grey areas, so it is essential that architects, builders and developers are properly advised when working on subterranean extensions to ensure they operate within the law and the conditions of the relevant local authority.
Salvatore Amico is head of town & country planning at Attwaters Jameson Hill