Musty Rooms, Cold Floors, Soft Spots: What Crawl Space Warning Signs Mean

Most crawl space warning signs trace back to one of three things: humid air meeting cool surfaces, water that has nowhere to drain, or wood that has stayed damp long enough to soften. A look under the floor tells you which one you have.

Why does the house smell musty in summer?

Air rises from the crawl space into the rooms above, so a damp, earthy smell on the first floor usually starts below it. In July, outdoor air in Indianapolis carries a dew point near 65°F (NOAA), and a vented crawl space is cool enough to turn that into dampness. Drying the air is the usual answer: see crawl space dehumidifiers.

Why are the floors so cold in winter?

In a vented crawl space, January air at an average of 28.5°F (NOAA) moves under the floor through openings Indiana's code places near every corner. Insulation that has fallen from the joists makes it worse. Sealing the space and insulating its walls keeps it closer to house temperature. Start with vapor barriers and liners.

Why does the floor feel bouncy or slope?

A soft or sloping floor often means a joist, sill or beam has lost strength, usually from years of damp, or that a support post has sunk. It can also be a structural issue beyond the crawl space. Someone needs to probe the wood. See crawl space repair for what that work involves.

Why is there water on the plastic after rain?

Water pooling on the plastic means the ground under the house is not draining. Indiana's code requires the space to slope to a gravity drain or a sump pit, and in wet springs Marion County's most common soil holds water close to the surface. The fix is drainage before any new liner: see crawl space repair.

Why is insulation hanging down?

Fiberglass batts between the joists soak up summer moisture, get heavy and sag away from the subfloor. Once they drop, they stop insulating and keep the wood beside them damp. It is a sign the air below is too humid. Pull the wet batts, then deal with the air: see crawl space dehumidifiers.

Why are the ducts or pipes dripping?

A duct carrying air-conditioned air is colder than the summer air around it, so water condenses on it like a cold drink. Drips land on the plastic or the soil and add to the problem. Keeping crawl space humidity down stops the sweating. Read about drying the air under the house.

Is growth on the joists serious?

White fuzz or dark spots on wood show it has stayed damp. Small patches on dry wood are common; spreading growth on soft wood needs attention. The moisture source has to be fixed, and the growth cleaned before a liner goes in. This Old House lists mold removal at $500–$4,000; see the cost page.

Could a high radon test be coming from the crawl space?

In a house over a crawl space, the dirt floor is the usual way radon gets in, and Marion County is EPA Radon Zone 1. A sealed liner with a fan drawing from under it is the EPA's most effective method for crawl space homes. Read radon and the sealed crawl space for the order of work.