Will the system also help with basement moisture?

Why this works

Soil under a basement floor sits at close to 100% relative humidity year-round. The earth is wet. The gravel layer under the slab is in contact with that wet earth. Without anything blocking the path, water vapor from the soil moves up through the gravel, through the slab seams and the cold joint at the foundation wall, and into the basement air.

A radon mitigation system reverses that flow. The fan pulls a small negative pressure on the air space below the slab. Now, any leakage path through the slab pulls air downward from the basement into the gravel, not upward. The water vapor goes outside through the vent pipe instead of into the basement.

Across most of the Rochester area, soils sit on shallow limestone with a high natural moisture content. That makes the soil-vapor contribution to basement humidity relatively large. It also makes the moisture side-benefit of a radon system more noticeable here than in drier parts of the country.

What the system does help with

• General humidity in the basement. Typical drop is 10 to 20% relative humidity.
• Musty smell. Often the smell is largely from soil-gas contact with finish materials. Pulling the soil air out usually clears it.
• Condensation on cold pipes and walls. Lower humidity means less condensation in summer.
• Mildew on stored boxes and furniture. Reduces with lower humidity.
• Damp-feel finish materials. Drywall and carpet near the floor often dry out and feel different to the touch.

What the system does not help with

• Standing water on the floor. Liquid water is not a soil-gas problem. Needs a sump pump, a drain tile system, or exterior drainage work.
• Active wall leaks. Water coming through a foundation wall is a waterproofing problem, not a radon problem.
• Cracked or settling walls. Structural water issues need structural fixes.
• Window well water. The system has no reach into window wells or the soil above the foundation wall.
• Plumbing leaks. Obviously not what the system is for.

What about a dehumidifier instead

A dehumidifier in the corner of the basement works downstream of the problem. It removes moisture from the air after the air has already entered the basement. It uses about 300 to 500 watts continuously when it runs.

A radon mitigation system works upstream. It prevents soil moisture from reaching the basement air in the first place. It uses about 50 to 90 watts continuously. The two are not redundant, since they target different humidity sources, but in many basements the radon system reduces dehumidifier runtime to the point where the dehumidifier becomes nearly unnecessary.

What changes the answer

• How much of the basement humidity is soil-vapor versus air infiltration. In a leaky old basement, outdoor air carries more of the summertime humidity. In a tight basement, soil vapor dominates. The radon system has bigger effect on the second.
• Whether the slab is well-sealed. A slab with lots of penetrations and a wide cold joint passes a lot of soil air. The fan reaches further and the moisture effect is larger.
• Whether there is active water intrusion. If there is, the water needs its own fix before any meaningful read on the humidity benefit.
• Crawl-space portion. Encapsulated crawl spaces with a sub-membrane radon system see the largest humidity drops of any install we do.