Roof mold/mildew

I live in New York. The front of my cape cod faces the North, therefore, the sun barely hits it. I have mold and yucky black mildew all over the Northside of the roof. It is a terrible eyesore. I had it professionally cleaned a few years ago. All that managed to do was temporarily clean it and destroy the existing roof. We have managed to mend the roof, but now have the mold/mildew back. Any suggestions on how to clean it? If I decide to get a new roof, under these circumstances, any specific type of shingle I should go for to avoid this from happening again?
Thanks for any suggestions.

 

Mold and mildew as you know are little living plants. they like cool, damp surfaces. It is relatively easy to take care of. Wash your roof with a liquid detergent. cut it about 1/2 with water and spray it on. This will kill the mold and mildew. They will grow back each year, so it is an ongoing project. However, you can put copper strips on your ridge and that kills the plants also. They can be gotten at any Home Improvemt store.