Mold can be a real problem in homes in the drizzly Pacific NW. Turns out that much of that problem comes from inside the home....
Most homes have high humidity from cooking, showering and laundry moisture. Mold will grow when the moisture condenses on cold exterior walls, usually in areas of poor ventilation and insulation such as along the baseboards. In most homes, especially older ones, there is little or no insulation at the rim of the floor which creates a cold zone.
The expensive solution is to tear off all siding and add proper insulation and a vapor barrier. Also install better insulation in the crawl space and attic. The practical solution is to frequently clean the areas with detergent and bleach. Also keep furniture away from the walls to allow some air movement. And educate the tenants to use the bath and kitchen fans. You can also install timers on the fan switches to turn on periodically through the day.
I have found that mold is less often found in homes with forced air heat and more prevalent with homes with baseboard electric. Baseboard heaters provide no air movement.
Guest post reprinted by permission by Bryon Moeller, Rose Asset Management Corp.