On 27/12/2017 10:52, Dave Plowman (News) wrote:
If water is getting inside a cavity wall, it could appear almost anywhere.
Although it would seem odd that it travelled several floors before
becoming noticeable.

It might be that being a 70's build, the brickies threw the snots down
inside the cavity wall, so you have a solid wall from DPC up about 3
brick courses. My 76 semi was like this.

If the coping stones have suffered thermal creep over the years then
water may well be running down the inner face of the outer leaf,
which would explain why the upper flats don't have a problem. The
water hits the bridged cavity when it gets to you. The wall ties
will also be covered with lumps of mortar from the brickies actions
(mine are like that).

I would insist on having a couple of corner bricks removed from
DPC up and a flexible camera poked in to see what the cavity is
like.

Also use a pair of binos and look for mortar damage. Has an
upper flat had a new boiler fitted into the wall above where
your damp appears ?. Are there any leaking gutters or downpipes
or overflows. Are there any leaking appliances in the flats
above that could be tracking around their concrete floors and
entering the cavity some way from where the appliance is ?.