Neighbour plans on loft extension using our loft extension wall

ThisIsWeird

silvercar said:

ThisIsWeird said:

I agree with what is said above - you do not want a gap left between the two structures. That might, however, leave concerns about boundary encroachment, but - other than emotive - this shouldn't cause any practical issues at all (aIui).
So that Silvercar - and other folk in similar situations, as this is a regular question on here - is fully informed, what are the various options available, coupled with their pros and cons? I'm guessing:
a) Leave a gap. Pros - can't think of any, other than 'emotive' over boundaries. Cons - hard/impossible to maintain. Will make construction for the neighb very difficult, and will likely lead to bad relations. It will look daft. 
b) build up to existing construction and make it a Party Wall, the same as the house below, with matching external finish. Ie, tiles match, and continue as one. Pros - sensible option. No visual/emotive 'encroachment'. Cons - neighb's might reasonably not want the same finish - eg new neighb wants cladding, or even render to match rest of house. Which leads to...
c) ditto as (b), but with a visual boundary separator/ marker to clearly differentiate the two constructions - there must be options there? Pros - removes any even emotive concern over 'encroachment'. Emphasises the separateness of the two. Prevents any awkward-looking transition betwixt two contrasting finishes. Cons - small additional complexity.
d) ?
Corrections/additions to the above?

d) Google seems to suggest a bonding gutter between the 2.

My main concern is that of structural integrity if they just use the existing outside wall as their internal wall ie they don't build up a new wall, but take the current wall and plaster it. Would that then mean they have encroached over the boundary and this could cause issues on sale?
Obviously, it won't make a difference to the current room size so has no impact in that regard.

That's why you check their submitted plans (for building control), and consult with the PWA surveyor - and even your neighbs themselves. I'm sure you'll find everything will be fine.

They aren't going to want any noise or thermal issues any more than you. And any possible 'boundary' concerns will affect them as much as you, too.

This is all normal stuff, and happens every day. Usual due diligence; have a nice chat with them, and agree that a joined construction makes most sensible. Ask if they've had their plans drawn up yet, and for a gander once they do. Chat about what their plans are for external finish, and how this would fit in with yours if different. Blah blah blah... :-)

How detailed are the 'plans' you referred to? If suitable for BC, then you could post them (ID redacted) on here for folk to check?