Oct 16 , 2019
Buy Pressure-Treated Lumber With the Right Amount of Treatment for the Job
Pressure-treated lumber is the logical choice for the structural part of your deck—the posts, joists, beams and other members you normally don’t see. Pressure-treated lumber can support more weight and span longer distances than cedar, redwood or other woods commonly used for building decks. It’s also much less expensive.
Pressure-treated lumber is rated according to the pounds of preservative retained per cubic foot of wood; the higher the number, the better the protection against fungi and insect attack. Select decking boards with the preservative concentration suitable for their use. Wood used in situations where it’s more likely to rot contains more preservative.
The three common ratings:
- Above-grade use (.25, sometimes .15). Typically used for decking, fence and railing material.
- Ground-contact use (.40). Typically used for posts, beams, joists and, again, decking.
- Below-grade (.60). Typically used for support posts that are partially buried below grade and for permanent wood foundations and planters.
Your decking boards will be tagged with the concentration and treating solution used. Use .40 material if you can’t find .25. CCA (chromated copper arsenate) is being phased out because of health concerns. ACQ (Alkaline Copper Quat) and other preservatives are replacing it.