Why does my basement get humid in summer?

Your basement gets humid in summer because warm, moist outdoor air meets the basement’s cool surfaces. When that air cools down, it can’t hold as much water, so moisture condenses on walls, floors, and pipes—like water on a cold glass.

A few things make it worse:

• Soil moisture can seep through porous concrete walls and floors.
• Poor airflow traps damp air so it doesn’t dry out.
• Open windows can bring in even more humid air on warm days.

Best fixes:

• Run a dehumidifier and aim for about 45%–50% humidity
• Keep windows closed in humid weather
• Improve drainage: clean gutters and move downspouts at least 6 feet from the foundation
• Insulate cold pipes to reduce condensation