ANSWER:High humidity is the leading cause of mold growth in the basement. Mold and mildew flourish when the relative humidity level is above 80%; therefore, all basements—finished or unfinished—should be kept at or below 50% relative humidity. In order to maintain that humidity level, use a dehumidifier and measure the humidity level often. The humidity level should be measured independent of the dehumidifier.
Keep a finished basement warm in the heating season. The best way to maintain a 50% relative humidity level in your basement is to keep it warm in the heating season. When the air is warming and cooling the air will actually create more moisture that may lead to mold and mildew growth so keeping the basement consistently warm at least at 58 to 60 degrees F in the heating season is best.
Evaluate your flooring. Carpet captures biodegradable dust and can be a breeding ground for mold. While a basement should be treated like part of the house, it is not the same as the upper levels of the house. There are different issues that happen in the basement environment and the same building principles don’t apply the same below-grade. Consider tile or vinyl flooring instead of carpet to eliminate the potential problems.
How is your storage? Anything biodegradable on the porous concrete floor may lead to mold problems. Avoid water or moisture problems by keeping boxes off the floor on a metal or plastic shelf. The shelving should also be at least 18 inches away from the foundation wall and 6 inches off the floor. If you have to keep cardboard boxes on the floor, put down a foil-laminated sheet of polyisocyanurate foam insulation on the floor and up against the wall to protect the boxes from the concrete slab and foundation wall.