Mold growth on inside walls can occur during the heating season, especially on the surfaces nearest the outside of your home. Moisture traveling through the air from the bathroom, basement, kitchen or other sources may condense when it comes into contact with a cold wall. By having well-insulated walls, you not only can save energy, but you also can reduce the likelihood of condensation and mold. You can raise the temperature of your walls by increasing the circulation of warm air from your heating system.
During the heating season, an indoor humidity level below 40 percent will prevent condensation in homes in most parts of the country. A lower level of humidity or extra insulation may be needed to prevent condensation in homes in very cold climates.