Pressure-treated lumber is softwood lumber protected by chemical preservatives forced deep into the wood through a vacuum-pressure process.
Pressure-treated lumber has been used for many years in on-ground and below-ground applications, such as landscape timbers, sill plates, and foundation.
A major advantage of pressure-treated lumber is its relatively low price in comparison with redwood and cedar.
When natural woods such as these are used, only the more expensive heartwood will resist decay and insects.
Three Grades of Pressure-Treated Lumber
Pressure-treated lumber is available in three grades. The three grades are designated by their pounds per cubic foot of preservative retention.
• Above ground grade (0.25 lb/cu ft) is to be used only 18 inch or more above ground.
• Ground contact grade (0.40 lb/cu ft) is used when there is contact with water or soil on or below ground.
• The third grade (0.60 lb/cu ft) is used when structural reliability is required, such as in wooden foundations and power poles.