Two systems, two moisture questions
- Sump pit
- Collects groundwater from below the slab; a failed pump or open lid can add moisture to basement air
- Radon mitigation
- A fan pulls soil gas from under the slab and vents it outside; a sealed pit lid is usually part of it
- Shared weak point
- Gaps around the pit lid, pipe penetrations and slab cracks
- Who to ask
- A radon mitigation professional for the fan system; a plumber or waterproofing contractor for the pump
How these systems relate to mold
Colorado is widely known for elevated indoor radon, and many Highlands Ranch homes have had mitigation systems installed, often at the time of a sale. A typical system uses a pipe through the slab or sump lid and a fan that draws soil gas out and exhausts it above the roofline. A working system lowers the pressure under the slab, which can also reduce how much damp soil air seeps into the basement.
Problems arise when the system is incomplete. A sump lid that was removed and never resealed, a cracked pipe joint, or an unsealed slab crack can let both radon and moisture into the room. The fan itself can also stop working without anyone noticing if there is no alarm or manometer being checked.
Sump pumps fail quietly too. A stuck float or a dead pump lets water rise in the pit, keeping the area around it damp. Finished walls near the pit are a frequent site of hidden growth.
Monthly look-around
- Check the radon system's U-tube manometer; the liquid levels should be uneven, showing suction
- Listen for the fan running where it is mounted, often in the garage, attic or outside
- Confirm the sump lid is in place and sealed if the radon system uses the pit
- Look at the water level in the pit after heavy rain; it should drop as the pump runs
- Test the pump by slowly adding water to lift the float, if the manufacturer allows
- Sniff and look at the bottom of finished walls closest to the pit
Questions for your contractor
- Will containment or demolition affect the radon system or sump lid?
- Who reseals any penetration you open in the slab or pit?
- Did you find signs that the pit has overflowed in the past?
- Do readings suggest moisture is coming from below the slab or from plumbing above?
General information for Highlands Ranch, not a quote or professional advice. In an emergency, call 911.