Side return extension and next doors lean to...

Young_worker

We live in a classic Victorian Terrace with rear extension. All fairly standard, so it means we have a side return at the back of the house next to the kitchen, which we would like to extend into....
However, next door neighbours on the party wall side of where the extension would be, have got a 'shed type' lean to on their side - bodge job and not properly integrated to their side. To add insult to industry its about 4 inches on to our side based on where the natural brick line between our houses is (didn't notice until we bought the house and surveyor never flagged encroachment in their report)....the shed also has windows facing into our side albeit 6 feet off the ground. We do get on well with our neighbours.
I am after any advice as to how feasible building into the side return is with this issue. I really don't want the hassle of a massive protracted battle but at the same time want to be able to do things to my house, rather than moving to get more space. 
As I see it we could build up to where their lean to is and make the best of a bad situation. Annoyingly we would be four inches short of our boundary but would avoid protracted battle and us trying to force them to move the lean to. Although we would't have access to their side for foundations due to the lean to?
Also there is a manhole where we would want to build the side return to - assuming this isn't too much of an issue to move with the water companies permission and our cheque book?
Thanks for any advice. 

Doozergirl

What about building up a new solid party wall? It would improve their lean to.  Worst case scenario, you could re-roof it for them with something cheap and cheerful.  Footings for an extension project beyond the actual wall anyway and if it isn't correctly built, it sounds like it would collapse into the trench.  

I think offering the upgrade would be better than them keeping something awful and you having to compromise and potentially damage something not worth saving.   The party wall
act may well be an issue, so building the new roof for them would probably be cheaper than a party wall surveyor, if you can negotiate it.  

I think most people would settle for an upgrade. 

As for building over the drains, it really depends on the route taken.  If you are very close, building control might accept rodding access from next door etc but we can't begin to help without knowing routes. 

Young_worker

I had considered that but then not sure if that would also open a can of worms as they would have to alter their lean to structure (excluding roof) and i don't want to write a blank cheque. The neighbours are older and aren't hugely open to change. 

Any ideas on the right profession to speak to? Architect, builder, surveyor etc? Its difficult to know where to begin...

Doozergirl

Party Wall Surveyor.  

But you will need your architect and structural engineer anyway so it's worth seeking their opinions first, but there is a party wall issue. 

Don't forget that any building, especially a dodgy one, close to yours is a potential source of damp and maintenance will be an issue. 

If it comes down, whether that be deliberate or not, you're responsible anyway so I don't see the point in trying to engineer around it if it's as bad as you say.  

DOH_a

Could you not approach them making them aware you’d like to infill the side return and offer a new shed or lean-to structure as part of the works?

If the neighbours were in agreement, you could build as close as 50mm between the external face of your new side wall and common boundary line. This would allow for an eccentrically loaded 600mm wide (or maybe even 450mm wide) foundation along with a small overhang for a flat roof. You’d fall the roof towards the rear and therefore removing any requirement for a gutter on the boundary.

If the manhole is public, it’d need to be removed and/or re-located outside the extension. Your water authority will have rules and regulations as to how close you can build to the public sewer. If however it’s private, then you can do pretty much what you want.

Some infill extensions can be challenging to get through Planning assuming you’re not going down the PD route?