At least once a year, check your exterior doors for possible water penetration. Check the weather stripping for tears and deterioration. Check the sills and exterior thresholds for damage. Is caulking needed? Can you see daylight through the door? If you can see light through the door, water can also get through, especially with a blowing rain. Sometimes this water gets under your floors without you noticing it until the damage is done. Thousands of dollars in damage can be caused by water penetration.