Baking Soda or Vinegar will work and it is better for the environment and animals than some harsher chemicals.
What this does is change the Ph level of the Moss to a point where it dies off - and it will take time for the moss roots to die off using baking soda - it will die completely roots and all with in 3 months - you should notice it starting to die very soon after application but the root system will take more time - 3 months.. (buy enough to cover your moss areas) - if the entire roof is covered you are in real trouble - the roof is too far gone and you can count on replacing it.
You can mix the baking soda with some water or use it directly on the moss.
Vinegar is more acidic it can harm different materials - so be careful if you use this route.
A nice link I found to expound on this further can be found [here^].1
You are probably aware of people using zinc strips to protect against moss growth - however this is not a good environmentally safe product. While it is very effective at prevention it can be harmful to aquatic animals.
And just to state this again
Don't pressure wash your roof.
To aid those who are banging this answer.
I am not sure if they have done their research or just relied on common practices. Common practice does not make it safe. Simple searches on line for environmentally (eco) friendly treatments for roof moss, and also similar searches for harmful effects of zinc strips will prove out my answer. So in order to save some trouble I will provide some links.
As for Zinc and its effects when NEAR a lake where you can have runoff going into a lake or pond - please take note that it should be avoided - which is the OPS concern .. see this link :
More info on Zinc and aquatic animals and vegetation
High zinc levels can interrupt the metabolic activity in soils, as zinc negatively harms microorganisms and earthworms, slowing down breakdown of organic matter that provides basic nutrition to plant roots. Some plants are naturally more tolerant of high zinc levels in soils, such as grasses, while broad-leaf weeds may be more sensitive. Vegetable crops tend to be much more sensitive to zinc levels, according to the University of Michigan.
Baking Soda converts the water to more alkaline killing the moss, Vinegar to more acidic killing the moss. I have not found any studies showing where the Baking Soda (sodium-bicarbonate) is harmful to aquatic life. As a matter of fact they use it when transporting fish in tanks to maintain ph balance and also other helpful effects.
If you are really concerned about the Lake environment - don't use
zinc strips or galvanized wire.