I live in a terraced house. There is a party wall at single storey level and not at first floor level (at the back). My 1st floor extension wall is on my side entirely and my ground floor extension is against the ground floor party wall which his single storey extension is built against . This historically is because the adjoining owner didn’t want the extension as he had a flat roof terrace over his single storey extension, so my previous owner built on his own land at 1st floor level rather than astride the line of junction. Now, the adjoining owner wants to build a two storey extension and enclose on my first floor wall. Will he simply be ‘using the space where a party wall would have been built ‘ or would there be future boundary issues?
He of course has the right to build a separate wall alongside my wall – there would then be a gap I take it, or could his new wall be tied into mine, otherwise it would get damp and debris in the small gap.
Firstly, if your neighbour now encloses your wall at first floor level it becomes a party wall and give him rights under the Act – e.g. should you want to make any structural changes to the wall in the future you would have to serve him with a notice. You can allow this to happen but most owners would want to be compensated. If the compensation was worked out using the formula in the Party Wall Act is would be half the current day cost of building the section of wall that is to be enclosed but as your neighbour has no right to enclose you may want to request a bit more than that.
Your neighbour does have the right to build a separate wall up to the boundary. If your wall is also built up to the boundary they would be abutting and therefore weathering would be straightforward.
If your wall was built inside the party wall then by allowing your neighbour to enclose you are giving up some of your land as well as creating a party wall. In that scenario, should you insist that the wall was built wholly on his own land then a gap would be created and it would be desirable to close it off with flashing/paneling.
My wall is on my boundary but not on the line of junction. I will allow my neighbour to build up to my boundary rather than limit him to up to the line of junction between our two terraced houses as seems better to have straightforward weathering rather than have to weather a small gap.
In your experience is it usual for a vertical damp proof course to go into the wall or toothing out/interlocking of his wall into mine to stop damp?
You would only consider a vertical damp-proof course if you wanted to stop dampness from passing between the 2 walls – as they will both effectively be internal walls that should not be an issue. The focus should be on ensuring that no dampness gets in to any gap that remains between the 2 walls – that would be done either with a flashing or if the gap is small with mastic.