Answer by
LeheckaG (1826)
Your "mold" is probably on a damp, shaded, or Northern-exposure of your home.
Certain metals or paints can reduce the ability of mold or algae/moss to grow;
but I have seen "mold" on some metal-siding structures
(granted not as common as on wooded-siding ones).
Some exterior & marine-paints contain anti-biotics.