de beauvoir house extension

House extensions in London are often built on, or very close to, a neighbour’s boundary. This article offers advice about how to negotiate the process.

We’d always recommend speaking to your neighbour as early as possible. Ideally this should happen once sketch plans have been produced, but before any application for consents has been submitted. If the neighbour finds out about your project through a planning consultation letter, they are likely to be more adversarial than if they had been involved in an early design discussion. Inviting a neighbour to contribute to the design before a planning application will allow a greater sense of ownership and participation for the neighbour, therefore reducing the likelihood of objections during the planning process.

Early neighbour involvement is also useful for the party wall process, particularly if you wish to build on (astride) the boundary. You can usually build up to your boundary without a neighbour’s consent, but building on the boundary itself requires their consent. Building on the boundary might effectively gain you an extra 150mm or 200mm of width internally in a rear extension. This could be valuable extra space, particularly in a terraced townhouse with a plot that may be only 5 or 6 metres wide.

Successful neighbour collaboration at ‘Stone House’

 At our ‘Stone House’ project in Islington, we refurbished a Grade II listed townhouse and extended to the rear. Early neighbour consultation was carried out, and the neighbour in fact decided to propose their own house extension at the same time. Architecture for London were also appointed as the architect for the neighbour’s project and this made the whole process much smoother! There were no planning objections and it made building astride the boundary the default choice.

house extension architect barnsbury

The previously dilapidated garden wall was also able to be rebuilt in brick, up to the height of the rear extensions without any objection and the costs for doing this were shared between the neighbours. If a project can be carried out in tandem with a neighbour, there are likely to be cost efficiencies for both neighbours, with reduced architect’s and other consultants fees, and cost efficiencies during construction if a single contractor can be used.

Consider potential issues on your neighbour’s land

Be aware of tree root protection areas. Even if you don’t have trees on your own land, your neighbours may have protected trees. This could affect the position and type of foundations that can be used for your project. An early appointment of a good arboriculturist and structural engineer is recommended.

 There may be restrictive covenants in relation to building close to a neighbour’s land. Any such covenants should be investigated with a solicitor. Cost effective insurance is sometimes available for proposed breaches where the covenants are historic and unlikely to be enforced.

passivhaus house extension

There is a possibility of Japanese Knotweed or ground contamination on a neighbouring property, even if not on your own land. These issues may affect your project and would need specialist investigation.

Planning and heritage considerations

In a heritage context, a building project’s impact on neighbouring buildings becomes more important during the planning and listed building consent process. An assessment will be made of the wider planning and heritage context, streetscapes, and views.

If your proposals include underpinning works to an existing heritage boundary wall, there is a chance that a heritage officer will determine it to be detrimental to the historic fabric. For this reason it may not be supported, even though the underpinning work itself is below ground and not visible.


View Architecture for London’s house extension projects. If you would like to discuss your project, please contact us.