When to use Pressure Treated Lumber

Learn when to use pressure treated lumber according to the 2012 International Residential Code. Based on information found in section R317 beginning on page 65 of the 2012 IRC book. Note that pressure treated pine is my building material of choice but can be substituted with naturally durable heart woods from redwood, cedar, black locust, and black walnut. There are also a number of chemical preservatives but I advise against any of these because of their toxicity.

Use Decay Resistant Wood

  • Floor joists in crawl spaces are closer than 18″ to the ground.
  • Girders in crawl spaces are closer than 12″ to the ground.
  • Any wood on a foundation wall and is less than 8″ from the exposed ground.
  • The ends of wood girders entering into masonry foundation walls with less than 1/2″ clearance.
  • Any sills or sleepers on a concrete slab that is poured directly on the ground without an impervious moisture barrier.
  • Wood siding and wall sheathing if it is closer than 6″ to the ground or within 2″ of a slab or walkway.
  • Wood furring strips that are anchored to basement walls below grade and without moisture proofing.

Common Sense

  • Any wood that touches a concrete slab or a foundation wall of any kind should be treated; no matter what the code says.
  • Any wood that is buried in the ground or set in a concrete footing should be treated.
  • Drop girders or beams that set in a cut out of a foundation wall should not have to be treated as long as they have a barrier between them and the concrete.

Remember that treated pine is only slightly more expensive than regular pine. If there is a doubt then use pressure treated pine. It is generally the only economic choice.

Treated lumber does have to be fastened with specific nails or screws. Electrogalvanized fasteners simply will not do the trick. They should be either double dipped galvanized, stainless steel, or copper (bronze).

Post set in ground should always be treated.