Around here, southern WI, I'm seeing many instances of green mold/algae or whatever it is appearing on the outside of vinyl siding. discoloring the siding. Most of the time it is more or less localized around a specific area on the siding. Maybe it is opposite a bathroom or a high moisture area. I'm sure this is happening in many other geographical areas of the country. What causes this and what is the fix? Is it related to my previous post about exterior wall construction? Many of the homes I see this on are relatively new or newer homes ( +/- 10 years). I havn't been called on to repair any of these yet, but I anticipate it in the future. Any input would be appreciated.