Our home is built into the side of a hill and my sewing area is also in our walkout basement. However, we don't have any problems (knock on wood) with a musty smell or humidity down there. We moved into this house in January after it had stood unoccupied for 3 years. When we did the walk thru with the realtor, there was a musty smell and it was moist enough that the peel & stick tiles on the floor had come completely loose in the lower level but the bank got 2 large (& expensive!) dehumidifiers and set them up and when we came back for the final walk thru before we put in an offer, the smell and moisture were gone. We were surprised when we came to the house after closing and found that the bank had failed to come retrieve the 2 humidifiers. Lucky us!!! We haven't had to use them again. Do you have the right size dehumidifier for your lower level? Depending on the square footage, you might need more than one.