How do you build right against another wall (side return extension)?

[Naknah]

I am just about to get planning permission to build a side return extension right up against our neighbour's kitchen wall like this (boundary on the right hand side):

I'm trying to draw the building regs drawings myself, not from scratch, but using a set that I had drawn a few years ago for a slightly different extension that I didn't end up building. The chap who drew them says he's too busy to amend them and I don't want to pay for a whole new set of drawings so I'm trying to draw them up and deal with the changes myself.

I'm stuck trying to figure out how the builder will build against my neighbour's wall. I have learnt that you can built on the edge of trench fill foundations like this:

but are the walls connected together in some way? Stuck together with something? We had a party wall surveyor out and he talked about tying the walls together but I'm not sure what he means. I found this photo of a side return extension being built in the way that ours would be:

My neighbour is a reasonable chap and will hopefully agree to anything sensible that we suggest to avoid a gap that could lead to damp etc.

 

[wessex101]

Generally the 2 structures should be kept separate to allow differential settlement.

Incorporate a slip membrane in the foundation and do not tie the wall into the neighour's wall. It is quite a specialist area and I would expect most party wall surveyors to insist on a detailed design by a professional with insurance.

 

[Naknah]

Thank you Wessex

 

[garyo]

Also consider the roof/guttering detail. What does your neighbour currently have soffit/gutter wise? Are you absolutely sure you know where the boundary is? Does his guttering/bargeboard currently oversail on to your side of the boundary, or are you building under his guttering in to his side?

Is good that you're on good terms with him.

 

[wessex101]

Generally the 2 structures should be kept separate to allow differential settlement.

Incorporate a slip membrane in the foundation and do not tie the wall into the neighour's wall. It is quite a specialist area and I would expect most party wall surveyors to insist on a detailed design by a professional with insurance.

I was a bit pushed for time yesterday so just wanted to expand my answer. The slip membrane is usually used if the adjoining foundation is shallower, the idea is to de-bond the new concrete foundation from the neighbouring foundation so any setllement in the new extension doesn't pull the neighbouring extension down with it. Obviously if the neighbouring extension is modern and has an adequate foundation then there is no problem just pouring the concrete up against the neighbouring foundation, chances are the neighbours foundation crosses over the boundary anyway so there may be an element of overlap.