Pressure Treatment
A process that forces chemical preservatives deep into wood fibers using a vacuum and pressure cycle to resist rot, decay, and insect damage.
In Detail
Pressure treatment is a wood preservation process in which lumber is placed in a closed cylinder, a vacuum removes air from the wood cells, then liquid preservative solution is pumped in under high pressure (150–200 psi). This drives the preservative deep into the wood fiber — far deeper than surface treatments can reach. The cycle ends with a final vacuum that removes excess solution from the surface.
The depth and amount of preservative retained in the wood (measured as pounds of preservative per cubic foot, or pcf) is the key specification. Higher retention = higher protection = appropriate for more severe exposure conditions. The AWPA Use Category system standardizes retention requirements.
Related Terms
ACQ (Alkaline Copper Quaternary)
The most common pressure-treatment preservative system for residential lumber, using copper and quaternary ammonium compounds to prevent rot and insect damage.
Use Category (AWPA UC System)
The AWPA Use Category system classifies pressure-treated lumber by the severity of its intended outdoor exposure, from UC1 (interior dry) to UC5C (saltwater immersion).