On 20/04/2018 11:37, newshound wrote:
snip

Are *the planners* saying it has to be reduced? Seems slightly crazy to
be in a dispute over 20 mm encroachment of facia/cladding. (Accepting
that neighbours are almost by definition irrational).


As I think I said last year, one way of approaching the issue is to ask
"could the neighbour do a mirror image loft conversion with *precisely*
the same dimensions?"

If the answer is no then ISTM the value of the neighbour's property has
been reduced; and someone has dropped a stitch. Luckily it seems from
the OP's further posts it was the builder who - mirabile dictu - has
accepted liability and undertaken to fix it. If that is delivered then
I'd say the builder is, despite the error, one of the good guys.

--
Robin
reply-to address is (intended to be) valid