I'm doing some work for some people who live in a very wooded area, who commonly have mold issues. They've asked me to look into the green mossy looking stuff growing in the shady sections of their roof...

can I just kill it with a bleach + water solution?

Your local roofing supply warehouse will have a cleaner.

When your done cleaning the roof install zinc strips about 1 foot below the ridge to keep the alge off the roof.

Tide clothes washing detergent and water.  

A coworker told me about this a while back and I tried it on my sidewalk.  It worked great, killed the moss in a couple of days and it didn't return.

Bayer makes a liquid concentrate packaged in a garden hose spray applicator. Last fall I went up on the roof and swept off / knocked off the moss and treated a couple of days before a good rain. Haven’t seen any moss since. As a preventative measure I’ll treat again in a couple of weeks.

where cn i get this Bayer "2-in-1 Moss and Algae Killer Ready-To-Spray" stuff?

Why don't you just preasure wash the entire roof?

Quoted: Why don't you just preasure wash the entire roof?

I am unsure of the age of the roof, so the shingles may or may not be strong enough to handle the pressure...

secondly, that would most likly fix the problem, but not solve the dilema of mold on thier roof, as it will most likly return.

Moss-B-Ware, that is what we use in the rainy NW.  It comes is a green can like a giant salt shaker.  You just lay down a line of the white powder like you are Tony Montana looking to get high, on the peak of the roof.  When the rain comes is mixes with rain water and runs down the roof killing all the moss.  One application per year should do.  In heavy moss concentrations, you can also sprinkle it right on top of the moss for extra killing power.  I do this every fall and it works awesome, it takes more time getting out the ladder and harnessing up than applying the stuff and letting it do it's thing.

I have been told to never pressure wash a roof with shingles, it does more damage than good because it removes little rocks in the shingles that protect your roof.

tag

Quoted: Moss-B-Ware, that is what we use in the rainy NW.  It comes is a green can like a giant salt shaker.  You just lay down a line of the white powder like you are Tony Montana looking to get high, on the peak of the roof.  When the rain comes is mixes with rain water and runs down the roof killing all the moss.  One application per year should do.  In heavy moss concentrations, you can also sprinkle it right on top of the moss for extra killing power.  I do this every fall and it works awesome, it takes more time getting out the ladder and harnessing up than applying the stuff and letting it do it's thing. I have been told to never pressure wash a roof with shingles, it does more damage than good because it removes little rocks in the shingles that protect your roof.

and where is this available?

www.zinsser.com/subcat.asp?CategoryID=4

Jeez, make everybody else do your legwork for you

Do a search at amazon.com they have it if you can't find any locally at a a hardware and garden store

Quoted: where cn i get this Bayer "2-in-1 Moss and Algae Killer Ready-To-Spray" stuff?

I picked it up at one of the big box hardware stores. I don't remember if it was the blue or orange big box? I've also seen it at our local 84 Lumber.

Quoted: I have been told to never pressure wash a roof with shingles, it does more damage than good because it removes little rocks in the shingles that protect your roof.

That is correct , unless you are about to sell the house.