First, remove large clumps of moss by brushing them off with a broom.
Next, using a garden pump sprayer, spray on a cleaning solution. You have several choices: a solution of 1/4- to 1/2-ounce copper sulfate to 10 gallons of water or a 10-percent solution of zinc chloride and 90 percent water.
Even a deck cleaner such as Deck Boss works just as effectively and might be less corrosive.
Whichever solution you use, be sure to cover shrubs and plants, and thoroughly rinse the roof and gutters with water.
Obviously, wear protective goggles and clothing, and work safely while on a ladder or wet roof.
After your roof is clean, nail Shingle Shield zinc roof strips along the ridge. Shingle Shields, from the Chicago Metallic Co. (1-800-638-5192 anytime), are 3--by-36-inch strips that react with rain to leach zinc oxide onto the shingles. The compound inhibits the growth of any further moss, fungus and algae, and that you can shout from the rooftops.
There's also have a Shingle Shield roof cleaner. I hope this helps, I stole it from this site, http://www.freepress.com/realestate/renews/qlon30.htm I have been a roofer for 17 yrs. and this is the best way to resolve fungus problems. I'm sorry Jim but giving someone a pressure washer for thier roof is very risky... I wouldn't recommend it... good luck Wayne.... From, Keiser...