thanks for that, il have to try and get my head around the slating system, i did help a builder with some but i found it a bit confusing, plus id say it probably isnt done correctly on this roof anyway, not sure whether it wasnt meant to have a fascia or they were really bad at measuring!
would i have to lift the battens too?
also you mentioned the bodge of fitting the pvc fascia over the old timber, is the thin pvc (10mm) fascia not meant to be put on a backer board? obviously not a bit of old skirting turned around as in this case, but a treated 7x1 say?
still pondering whether i could extend the slate some easier way, not the right job but i find the renovation side of things takes so much energy and headspace just to try and get things vaguely ok, i can see why people say,knock old houses down!!, not sure id go that far, but having a new block extension put on was interesting to see how efficiently it went up, although maybe that was just having a builder who new what they were doing, not just me poking about!!
thanks again
carl