What is expected in the forest is not beneficial when it comes to your deck, basement exterior wall, or retaining wall. One easy way to avoid rot is to avoid wood altogether: build with non-organic materials such as metal, CMU blocks, and masonry retaining wall blocks. But if you want wood, then choose pressure-treated wood, preservative-treated wood, or naturally durable wood. At the home center, pressure-treated wood can usually be identified by its numerous incision marks. It is easy to imagine that the copper azole, type C, preservative has been injected into the wood at those points. Sleepers or sill on top of concrete floors Vertical posts or columns resting in or on concrete Direct contact with the earth Retaining walls Some house siding elements Some subflooring Some joists
Actually, the incisions help open the wood and allow the preservative to be forced into the wood cells under high pressure in massive metal tubes nearly half the length of a football field. While pressure-treated wood is twice or even three times more expensive than conventional kiln-dried lumber, your gain is the peace of mind in knowing that your project will not be affected by moisture or pests such as termites or carpenter ants. Building code requires pressure-treated wood in numerous applications. Following are selected instances where you might be required by code to use pressure-treated wood for your home remodeling projects. Note that this requirement is only for exterior walls, as these may wick moisture onto the lumber. Interior walls are within a climate-controlled environment and are presumed to be free of moisture. This requirement is especially relevant to basement finishing. Bypassing this code requirement can lead to the basement wall members soaking up moisture. Because basement walls are hidden behind drywall or other wall covering materials, the wall framing members are not exposed to light and air. In a closed environment of this type, wood rot and devastating mold can quickly set in. When you have a vertical wood post or column resting on concrete or other masonry, and that concrete/masonry itself rests directly on the earth, then the post/column must be pressure-treated. Pressure-treated wood is not required if an impervious moisture barrier and a 1-inch metal or masonry pedestal separate the post from the earth by a total of 6 inches in basements or in weather-exposed locations. As with the requirement about basement masonry walls, this is meaningful in basement finishing applications, but this time with regards to structural support. Sleepers and sills of any nature contacting concrete or masonry must be pressure- or preservative-treated. This is why pressure-treated lumber is required whenever the lumber is embedded in, or in direct contact with, earth. Fence and decking posts are the most common types of wood that come into direct contact with the earth in residential properties. swaite / Getty Images This is not an exhaustive list of all instances when pressure-treated wood is required. See ICC IBC (2012) 2304.11 for more applications of pressure-treated wood with respect to home renovation and building. Building code in your area may allow for any type of preservative treated wood, not just pressure treated. It also allows for what is termed “naturally durable” wood. The American Wood Council says that cedar, black locust, and redwood are a few of these types of woods that are naturally durable. All references to “earth” mean the actual dirt, not ground-level or grade.
