Join Date: Jul 2000
Thanked 238 Times in 225 Posts
Rep Power: 18
Looks like 'artillery fungus', a very common fungus that grows on tree bark in wet climates.
Any 'caustic' type detergent will usually DISSOLVE it: Mild lye solution, TriSodiumPhosphate, SodiumSilicate, .... all the industrial strength 'caustic type' detergents - use with caution. Apply and 'let soak' as it takes time to dissolve. Clorox, etc. can kill it but doesnt dissolve it and the remaining 'dead fragments' then can become the nutrient source for other fungi.
Remaining 'shadows' can usually be easily 'bleached' with oxalic acid (wood bleach) - from a paint or hardware store.
Most probably you will see the same 'growth' on ALL the roofs of buildings in the same area.