Do I Have to Notify the Leaseholders of the Flats in the Adjoining Property?

by The Party Wall Surveyor


We’re planning a basement extension and will need to notify the owners of the property next door. It is split in to 3 flats but the freehold is jointly owned by the 3 leaseholders. Do we notify the freehold company, the 3 leaseholders or both?


The starting point is the definition of an owner and that is confirmed in Section 20 of the Act as any party with an interest in the adjoining property of greater than 12 months – that means that the work is potentially notifiable to freehold and leasehold owners (assuming that the leases have more than 12 months to run which is very likley).

The next step is to establish whether the work affects the adjoining owner in a way that is described in Sections 1, 2 or 6 of the Act. Sections 1 & 2 are quite straightforward but which of the leasehold owners must be notified of works falling under Section 6 is a slightly grey area as it’s not specifically defined in the Act. This is what the relevant section states:

This section [the section that deals with excavation] applies where … a building owner proposes to excavate, or excavate for and erect a building or structure, within a distance of three metres measured horizontally from any part of a building or structure of an adjoining owner and any part of the proposed excavation, building or structure will within those three metres extend to a lower level than the level of the bottom of the foundations of the building or structure of the adjoining owner.

Most surveyors take the ‘measured horizontally’ reference to mean that the owners of flats at all levels should be notified if their demise is within 3.00m (measured horizontally) but some would disagree. The important thing is to be able to justify your decision. The arguments against notifying leasehold owners of the upper floor flats is that the risk of damage is lower than to the ground floor flat and that it would get ridiculous if an owner planning works falling within Section 6 of the Act was unfortunate enough to live next door to a high rise block (although that would tend to have deep foundations).

Follow up query

Thank you for your response but can you please also clarify which owners have to be notified of the new wall that we propose to construct at the boundary as part of our rear extension?


I’m assuming that you mean that the wall will be built up to the boundary but wholly on your land (a new wall astride the boundary – a party wall – could only be built with the adjoining owners’ express consent).

In short, you need to notify all parties that have an interest in the section of land which adjoins the wall that you intend to build. As it’s a rear extension, it is the adjoining owners’ back garden that is relevant. The garden will form part of the freehold so they must be notified but also whichever leaseholder(s) have use of the relevant section. That’s typically the lessee of the ground floor flat but not always.

It is a Line of Junction Notice that you need to serve (under Section 1 of the Act) and the notice period is 1 month.