On 7/21/2014 2:03 PM, Oren wrote:
On Sun, 20 Jul 2014 20:43:27 -0400, Frank
wrote:

OP need only google algae siding images to see.

I get it in shaded areas. Wash and bleach but it keeps coming back.

Often it happens on the North side of the house, lack of sun shine. It
can help to thin any large trees to allow more sunlight on the wall.

YMMV


Yup. That's the worst side and trees were thinned. Fortunately in my
case nobody but me can see it.