Spraying with salt water on a low setting power washer might work. The salt will kill the moss, and prevent it from growing back. Might be cheaper to just invest in a power washer to do this every year.

To prevent the moss from growing after you kill it use Zink strips on your roof. I learned about them on ask this old house.

One example.

http://www.zincshield.com/home.html

salt water seems to be very efficient in getting rid of moss, you should lay dry salt throughout your roof so it wont allow growth. you can also use herbicides.

We live in Portland Or where we get extended periods of moisture and grey skies. As you can imagine, we have moss on our roof. What is the most effective method for removing it and preventing future growth?

Does a copper wire strung across the top really work? If so, what gauge should be used?

Can pennies be used? If so, does the copper plating need to be removed to expose the zinc core?

What about the expensive zinc/copper strips, any feedback?

What's the best method for removing the existing moss and soil underneath it? I've been using a narrow putty knife, but I can see that'll take me an entire day to get the whole roof.

Thanks in advance for any info!