On a vinyl job moisture gains access to the back side of the vinyl at all sorts of points.
Vinyl siding chimney flashing.
Follow the directions of the siding manufacturer for.
Nail j channel for vinyl or metal siding onto the flashing.
Then an ice water shield underlayment must be installed around the chimney.
Inspect the sidewall around and underneath the fascia and inside the house for signs of moisture damage and repair any rotted areas.
This is why there are drain holes at the bottom of the laps to let it back out.
Leave a 1 4 inch gap between the step flashing and wood siding or cement board.
Gable ends are their own can of worms as reguards uphill chimney flashings.
Install the kickout flashing underneath the first shingle photo 1.
Add felt if needed before nailing the new wood on and prime the new wood on all four sides before installing it.