Hi, our bedroom ceiling has been starting to develop an issue in that it’s damp below the valley rafters (although actually was dripping a couple of months ago, but I found the gutter the valley was draining into was overflowing at the wrong end!, and I assumed back into the wall - but that all feels dry now I’ve been able to access the bottom of the valley.
However we’ve still got an issue, and I took the top 4 slates off the roof and the membrane below was all dry - this is lower than the issue inside.
Some of this blue membrane overlaps (found this off cut) the valley lead and so as it feels as tho it’s capable of absorbing moisture, therefore could it be wicking from the valley, and into and up the timber?
I’m sure this is a very simple question but I can’t find what is correct, and if the company who replaced our roof many years ago didn’t follow good practice. So before I take the slates from bottom up, I’d appreciate a bit of guidance so I can put / see what should be correct.