valley roof

My job for the weekend was to remove the polystyrene tiles off the ceiling of one of my upstairs rooms. As soon as I slipped a putty knife behind one, the lath and plaster crumbled and disintegrated: Removing the weakened plaster shows the laths have rotted away and the bits that are left are...

Hi all, Just after some general advice about an extension to our existing pitched roof. I attach a plan for reference (apologies for the sketchy scrawl!). The boundary of the existing pitched roof is demarcated by the blue dots. There is also an existing flat roof (single storey only)...