Watch this video from This Old House to learn how to install a rain diverter.
1. Sand underside of flashing with 80-grit sandpaper to help paint adhere; wipe surface clean.
2. Spray-paint bottom surface and up-turned edge of flashing to match color of roof.
3. Cut flashing in half using aviation snips.
4. Use flat pry bar to loosen stuck roof shingles.
5. Lay one flashing piece upside-down (painted side facing up) on roof at an angle and slip it under the shingles; repeat for the other flashing piece.
6. Secure the flashing with roofing nails; be sure to place each nail under a shingle.
7. Cover the nail heads and seal down each shingle with caulk.
8. Spray the roof with a garden hose to test the effectiveness of the rain diverter.