Moisture Testing for Crawlspace and Basement

Moisture emitting from a wet basement or crawlspace is not only unhealthy for the occupants of a home, it can cause damage to vinyl, tile, laminate and wood flooring.

Hardwood flooring is especially prone to cupping and buckling when exposed to damp, or wet basements and crawlspaces. Moisture should be tested and any resulting issues should addressed before wood flooring is installed.

Unfortunately, most homeowners don’t pay attention to their crawlspaces or unfinished basements unless they actually find standing water. But the damages from moisture vapor are equally damaging.

There are two very distinct sources of damp in basements and crawlspaces, with distinct means of control – rising damp, and cold surfaces. Because humidity is lowest during the heating season, this test will be more accurate when the weather is hot and humidity is higher; typically during the spring, summer and early fall.

Below is a simple way to determine rising damp from condensation on cold surfaces:


On concrete or cinder block:
• Select a 12” square of the damp wall or floor and wipe it dry.
• Place a 12” square piece of plastic over the area, using tape or weights to hold the film edges down.
• Lay the plastic down and weigh down the edges.

On sand or soil:
Lay the plastic down and weigh down the edges.

Monitor the film until fogging or droplets form (a day or two).
• If the droplets are underneath the film, the problem is rising damp, and a source of external water needs locating and solving.
• If the droplets are on top, the problem is warm humid air entering the space and forming condensation on the walls, floor joists and sub-floor.