We are planning a Rear Extension and our Neighbours are only happy for us to Build up to the Boundary and not extend over it.

by: The Party Wall Surveyor


We will be building a rear extension in a semi detached house and have informed the adjoining neighbour of our intention and provided plans. We had hoped to extend the line of junction with the adjoining house to maximise the width of the extension however they have stated they are only happy for us to build up to the boundary and not extend.  We had hoped they may also wish to extend and share a party wall however this is not the case.

My questions are as follows:

  1. Can we build the wall right up to the boundary line or is there a further space that must be left?  We wish to maximise the width of the room so building right up to the boundary is preferred.
  2. In the future, new owners may wish to also extend.  I would assume they would then build their wall against ours on the boundary line thus sealing the outside of our wall.  Do the 2 walls then form a party wall, what complications can this cause and what precautions can we take at this stage if any?

We are only recently moving in to the house so want to ensure a good relationship with the current neighbours however want to also maximise the space and quality of the extension.


You can build up to the line of junction but no part of your building, including the fascia, guttering, capping stones etc. should project beyond it.

Yes, your neighbour could also build up to the boundary but the walls would remain in separate ownership. To prepare for this eventuality I would recommend that you do not project your foundations beyond the line of junction (although the Act allows you to if it is necessary) – is it possible to lay wider foundations and build a wall on the edge of them.

It is a shame that your neighbour will not allow you to build a new wall astride the boundary as that would be the best solution.