Basement smells musty
Urgency
3/5
Depends on what you find; start here$150-$2,500Typical repair cost
Likely causes, most common first
- Chronic humidity above ~60% feeding surface mildew, the most common and most fixable
- Minor seepage behind stored boxes/finished walls you haven't seen yet
- Dead airflow zones: blocked returns, never-opened rooms, carpet on slab
Do this right now
- Buy a $10 humidity gauge; data beats noses
- Run a properly sized dehumidifier to 50% and re-smell in a week
- Pull stored items 6 inches off exterior walls and check behind everything
DIY or call a pro?
If 50% humidity kills the smell, you've solved it. If it persists or you find staining, the source hunt (grading, gutters, seepage) is worth doing BEFORE any basement finishing dream (see our basement guide).