Before getting into the issue lets get a hang of terms used, using an image(That's how I do it. Some of the roofing components aren't there, like plywood sheet and Sarking).
Prev resident of the house had the issue of water dripping from fascia.
The Blue arrow shows the mark created by dripping water(prev resident)
Reason:- Water was backtracking its way inside the softfit and was finding its way to fascia
Solution:- Install drip edge under the roof and over the rain gutter. Used Aluminum sheet to create drip edge, which works.
Placing the cut sheet under the roof and over the rain gutter, like so
The metal is not touching any other metal so there won't be any reaction - Topic to search for is "metallurgy".
Even the Rain Gutter was dripping water because water was backtracking from polycarbonate sheet.
Solution: Used the excess polycarbonate sheet to create something of this sort(see image below). Its tested and it works.
This tweak goes under the fixed polycarbonate sheet - Use epoxy to stick the piece to polycarbonate sheet, Gorilla glue won't work.
Sample of how it goes under the sheet(used clips to test the tweak before fixing it permanently ).
