especially during this time of the year. I would first do as Jay would say, remove branches, and let in the sun and ventilation. You have this growing because you are giving this plant what it needs, warmth, moisture, and no sun.
Bleach will kill this but will also streak your roof, power washing will also work but too much pressure will explode those shingles. I would opt not to do those.
Let the sun in and let good ventilation in. Do you have this problem in the spring and summer?