I want to use a J channel rain diverter under the shingles on my patio roof. How do I avoid moisture under the shingles when/if we have snow? Have seen this done but they didn't address this issue on the video. Perhaps it is a non issue and I am just over thinking this.
I hope your not thinking about using a piece of vinyl J moulding for this?
Where the deverter gets nailed to the roof it needs to be at least 3" up under the edge of the shingle.
A simple L shaped piece of coil stock is the simplest way to do it.
I do a 1/2 seam, then make the next bend at 1" and cut it off at 3 or 4".
The seam adds strength to the raised area.