Why it happens
Why Houses Around Here Turn Green on One Side
If you've noticed a green or black film creeping up the north wall of your house, or along the eaves where the sun never quite reaches, you're looking at mildew and algae. Houston's heat and humidity give it everything it needs, and the shade from all the pines and oaks in Spring and The Woodlands keeps those walls damp long after a rain.
Then pollen season comes and leaves a yellow layer on top of it. Left alone, that growth works its way into the texture of stucco and the seams of siding, and it starts to make a well-kept home look older than it is.
A soft wash takes care of it at the source. The cleaning solution kills the mildew and algae instead of just knocking the top layer off, so your house stays clean a lot longer than it would after a quick blast with a pressure washer.