David Hearn wrote:
Our 1930's semi currently has separate plastic guttering systems, with
each half having their own single downpipe, although our downpipe is
cast iron. We've lived there over 10 years, with our elderly
neighbour living there far, far longer. Neither gutter have been
replaced in that period, but as neither is cast iron, both have been
replaced at some point.
Our neighbour approached us to say that she's replacing her guttering.
Apparently she also mentioned something about having a damp problem,
but I'm not certain where it is, or whether the guttering replacement
is meant to resolve this. Apparently there was some discussion about
whether we wanted our side replaced as well - we can't afford this.

Today we've been asked to confirm whether we want the guttering
systems connected. At present they're separate, and doing a quick
check around neighbouring properties, there's a mix of both joined
and unjoined. I suspected originally they were joined, but over the
years some have been separated as one half replace theirs.

When I said I was happy to leave it as is, she was fairly polite, but
pressed the point that (she was advised?) as there would be a gap
(however small), that water could run down and cause damp. She
repeatedly said that she's fine with our decision, but to make it
clear she's warned us of the potential problems. I think she was
trying to make it clear that if things go wrong, its our fault.

My reason for not wanting them joined was mainly that it's not been a
problem for the last 10 years (and likely longer), and that I'd like
to avoid shared systems were possible to prevent potential disputes
should one side leak/overflow etc.

What do people recommend? Should we connect our guttering (assuming
it's possible) or keep separate? Is there a real chance of damp due
to the gap, or is it best to keep as-is?

Just tell her that you haven't had any problems in all the time it's been
speperate so there's no need to replace anything at this time.
Her fitter is pressurising her into talking you into having yours done,
probably with the offering of a price reduction in her job - the fact is,
hundreds of thousands of semis have seperate systems without problems, and
if she's having damp problems at the join now, it's probably because her
existing gutter is running the wrong way - toward the joint instead of away
from it and towards the outlet.