Pressure-Treated lumber is treated for protection against termites and rot. Ideal for a variety of applications including decks, play sets, landscaping and other outdoor projects where lumber is exposed to the elements. When used properly it is both safe and environmentally friendly. Treated wood is typically still wet when its delivered to The Home Depot or job site. As it dries, you should expect slight changes in width and length. As lumber dries, it may split, cup and warp. This is more likely to occur to occur in lower-grade boards, where knots and uneven grains are already present. Each piece of lumber is unique and carries physical characteristics that may include the following: knots, warping, shrinkage, swelling and/or splitting.