Building a Rear Extension Along a Boundary Line – What is The Best Option?

by: The Party Wall Surveyor


We have planning permission to build a single storey rear extension and have been given permission to build along the line of the boundary with our neighbour. A wooden fence, which according to the land registry is owned by our neighbour, marks the line of the boundary. It is highly unlikely that our foundations for the extension will be bellow that of our neighbours house.

If we build up to the wooden fence bringing our extension in so that it doesn’t go along the boundary line, are we still governed by the Party Wall Act?

If we agree to remove the wooden fence, and replace one wall of our extension as the new party wall that our neighbour can build an extension off, then presumably we will need a Party Wall agreement?

If we build wholly on our land – making the extension narrower and the footings not going deeper than his house, would we be able to proceed without a Party Wall Agreement?


The best  position for the wall would be astride the boundary i.e. in line with the wall which separates your two properties, although that would require your neighbour’s consent.The next best option would be to build up to but not over the boundary line but that would be notifiable under Section 1 of the Party Wall Act. Although your neighbour could not stop you from putting your wall there he could dissent to the notice and surveyor(s) would have to be appointed.

If you keep your wall back from the boundary slightly (enough to make it clear on a drawing) then a Section 1 notice is not required. So long as you do not excavate deeper than the base of your neighbour’s existing foundations you will not have to serve a Section 6 notice either.

There are a couple of other things top bear in mind. If you keep your wall back only slightly it will make the building process difficult. It is possible to build a wall from the inside but not so easy to point it if the outer skin is to be brickwork like the main part of the house. Perhaps you could agree with your neighbour to use an ‘Agreed’ surveyor and go for the best option and maximise your space.

Without notice you will not be permitted to project your foundations over the boundary, although it is normally possible to lay a wider foundation (600mm as opposed to 450mmm) and build the wall on the edge of it.