Hey folks,
I have a colonial in the Baltimore suburbs with a four-sided hip roof with one central ridge along the center 1/3rd, and no valleys. It's covered in "architectural" asphalt shingles. The shady sides (the Northern sides) are beginning to show black streaks -- which from what I understand is a type of algae.

The best way to permanently prevent this - from what I've read on the web - is to install copper or zinc flashing under the top course or ridges of the roof. Has anyone here done this successfully?

Because I have a hip a roof, I'd also need to install flashing under my ridge caps as well - since my top course is a relatively short horizontal run in the center of the roof.

Can I simply slip in a piece of flashing and then get in there with some roofing cement (using a caulk gun) every few feet to hold it in place? Any reason this would be a bad idea?

Thanks in advance for any help.