Mold is caused by humidity. One way to increase humidity in building's shell is to have humid air and large thermal gradients in poorly ventilated areas. Opening windows does not help in the humidity that gets into structures when air with vapour enters colder structural parts of the building and releases it's moisture. Warmer houses-> the point where moisture is released moves closer to outer wall. That's at least my laymans understanding of one of the mechanisms which affect houses.
