"NY" wrote:

Exactly. Can you draw a diagram of how the window and your two houses are
arranged?

I might be able to put a photo online but I haven't yet sorted out a
replacement for Photobucket; I'll see.

How can either of you measure the exact position of the boundary line /
party wall?

I think he's calculating the position of the boundary based on the distance
between the two closest adjacent rear windows in our back walls. The window
openings were 4.5 brick-widths apart, so the boundary is presumably at the
2.25 brick-width position.

This is complicated now though because the rear wall of my bungalow has been
moved backwards into the garden by a metre and the new window openings are
quite different. But photos exist of the old wall in place.

Is the fence between you exactly on the boundary...

No. The fence, for some reason, is some 6-8 inches his side of the boundary
(if the 2.25 bricks calculation is correct).

Until all this business started I never looked closely at the placing of the
fence and automatically assumed that it accurately marked the boundary. I
do wonder now if the builders made the same assumption and took the fence as
a datum line for locating the newly-moved wall and therefore the dormer too.
If so it doesn't necessarily mean that there is an overlap but it would
place both wall and dormer closer to the boundary line than in the plans.