pressure-treated lumber is wood that is engineered for use on outdoors. Pressure-treated wood typically starts off with one of the spruce, pine or fir varieties or other similar softwoods, and a sealant formula is pressure-applied to the wood so that the sealant soaks into the core of the wood
Until 2004, pressure-treated wood for residential use was preserved with chromate copper arsenate, and the level of treatment was generally the same for all lumber. This formula was quite effective in protecting the wood but had issues with toxicity, not only for those who worked with the wood but also for any animals that came into CONTACT with the lumber. Because of concerns over arsenic’s toxicity, CCA has since been replaced for residential use by a host of preservatives, some of which have themselves been replaced by even newer formulations. Compared to CCA, these preservatives is expensive because contain higher amounts of copper, so manufacturers produce pressure-treated lumber with different retention levels.