The less expensive solution is to spray wash the roof with a 50 percent mix of water and bleach to get rid of the algae.
Roof algae cleaning solution.
They re likely to damage the shingles just be sure to wet your foundation plantings first and rinse everything in clean water when you re done.
The second method is to spray on a coating of stain blocking solution defy stain blocker for roofs is one product but there are other brands as well a stain blocking product can buy you up to three years of protection from algae.
Put in a spray bottle to apply to small patches.
No pressure washers please.
Trying to diy roof algae cleaning with solutions such as bleach and water could lead to expensive roof leaks or further moisture getting trapped beneath your shingles.
Do not attempt to remove algae from your roof alone.
For a larger more involved surface area pour the formula into a pump sprayer.
If it is too late to prevent algae treat the problem instead.
Also there are other related expenses which amounts to a pretty significant number most of the times.
A homemade cleaning solution can be mixed using a quart of chlorine bleach and a gallon of water with one fourth of a cup of trisodium phosphate stirred in.