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Can My Neighbour Build an Extension Up To My Boundary?

Party Wall Boundaries

What is a ‘Boundary’ and does a neighbour have the right to build an extension up to it?

Written by Icon Surveyors

What is a ‘Boundary’?

A ‘Boundary’ is simply the dividing line between two or more plots of land each usually belonging to separate owners. The ‘Boundary’ can form as a literal line that divides the separately owned plots of land but more commonly is in the form of a wall that could be a part of a single building or two or more separate buildings. These types of walls are more commonly known as ‘Party Walls’. As a rule of thumb, provided the wall forms a part of an adjoining building or plot of land, it is a ‘Party Wall’.

The Party Wall Etc. Act 1996, stipulates the various types of Party Wall that Act covers. An example can be found in section 1 of the Act which focuses on Party Fence Walls. This is a wall that sits on the boundary of two or more plots of land but has no other buildings attached to it. This could be a garden wall, one that you might find in the front or back garden of a semi-detached property or a wall that separates farmer’s lands and fields. This type of Party Wall is different from a Party Wall Structure which usually applies to buildings or structures such as walls that form a part of a building they can be both vertical and horizontal and include ceilings and floors of apartment buildings or maisonettes.

Party Wall Boundaries

Can I build an extension up to the ‘Boundary’ of my neighbour’s wall?

Under, the provisions of the Party Wall Etc. Act 1996, any building or land owner who wishes to construct an extension on their land is permitted to do so whether or not the extension is up to the neighbours ‘Boundary Wall’. The difference being the varying degree of legal obligations that are put upon a building owner who wishes to encroach on and/or use their adjoining neighbours part of the wall to carry out the works. If the extension involves an excavation that is 3 metres or less from the party wall, the building owner has a legal obligation. This is to obtain consent from all adjoining neighbours prior to commencing with any of the works. This is done by serving all affected adjoining neighbours with a section 6 Notice.


Say a building owner constructs an extension on their own land, without excavating within 3 metres horizontally. This can be from any part of the adjoining neighbour’s buildings or structure. Then the building owner is free to build an extension ‘up to their neighbours Boundary Wall’. This would also be the case if 6 meters of meeting a plane drawn downwards in the direction of the excavation building or structure of the building owner at an angle of 45 degrees to the horizontal from the line formed by the intersection of the plane of the level of the bottom of the foundations of the building or structure of the adjoining neighbour with the plane of the external face of the external wall of the building or structure of an adjoining neighbour.

Essentially, if a building owner carries out an extension that finishes on their side, no action is needed. They are not obliged to do so under the Act.

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