Pressure-Treated Lumber
Pressure-treated lumber is wood that has been infused with chemical preservatives under high pressure to resist rot, decay, and insect damage, extending its service life in ground-contact and exterior applications.
In Detail
What Is Pressure-Treated Lumber?
Pressure treatment forces preservative chemicals deep into the wood fiber using a sealed cylinder and high pressure. The result is lumber that can last 20–40 years in ground contact, compared to 1–5 years for untreated wood of the same species.
Modern residential treatments primarily use MCA (Micronized Copper Azole) or ACQ (Alkaline Copper Quaternary) preservatives, which replaced CCA (Chromated Copper Arsenate) for residential use in 2004.
Retention Levels
- Above-ground use: 0.06 pcf (pounds of preservative per cubic foot of wood)
- Ground-contact use: 0.15 pcf
- Critical structural/freshwater: 0.40 pcf
- Saltwater splash zone: 0.60 pcf
The retention level — stamped on each piece — determines where the lumber can be used. Using above-ground rated lumber in ground contact is a code violation and will lead to premature failure.