Is Pressure-Treated Wood Required for a Basement?

Mandates

• The International Residential Code, or IRC, the leading regulatory code for home building, mandates that builders must use pressure-treated wood in certain situations. When wood comes into contact with concrete, the wood may become vulnerable to decay, as concrete in a basement tends to collect moisture. The IRC, which most local building codes follow, mandates that wood framing members in contact with concrete walls and less than 8 inches from exposed ground must contain a preservative. Sills, the long beams at the bottom of a wall, must be pressure treated when they contact a concrete floor unless an impervious moisture barrier is placed between the two.

Studs

• The wall studs might indirectly suffer damage from sills that touch a basement's concrete floors, even if they do not touch any concrete themselves. Pressure-treated sills, although they will not rot from contact with concrete, may still transmit moisture from the floor to the bottom of the studs, according to the Green Building Advisor website. It recommends placing a foam sealer between the concrete and the sill to prevent moisture from getting into the sill.

Fasteners

• The preservatives placed in pressure-treated lumber usually contain significant amounts of copper, which can corrode steel fasteners. "Fine Homebuilding" magazine recommends the use of either copper or stainless steel fasteners when working with pressure-treated wood. Galvanized fasteners, which have a coating of zinc, also work well. For galvanized fasteners, the thickness of the zinc coating determines how long the fasteners will remain resistant to corrosion.

Permanent Wood Foundation

• One use for pressure-treated wood in basements involves building the entire foundation out of wood rather than concrete. Called a permanent wood foundation, or PWF, the lumber for this type of foundation must contain preservatives since it's in contact with the soil and would decay if not treated. The system has proven resistant to moisture and insect damage in tests done by the U.S. Forest Service. One advantage of PWFs is that they provide a warmer and less damp finished basement than concrete foundations.