The purpose of putting plastic under sill plates in your basement

Putting plastic underneath wood plates (also called sill plates) in a basement or on a concrete slab serves an important purpose:

Moisture Barrier-Concrete is porous and can absorb moisture from the ground. Over time, that moisture can transfer into the wood, leading to:Rot and decay of the wood.

Mold growth, which can affect indoor air quality.

Structural damage if the sill plate deteriorates.

What kind of plastic?Typically, 6-mil polyethylene sheeting is used as a vapor barrier. It’s placed between the concrete and the wood to prevent direct contact and block moisture.

Code and Best Practice In many areas, building codes require a moisture barrier or that pressure-treated wood be used for sill plates in contact with.