The current formulations of preservatives have been shown to keep wood solid for two decades or longer, depending on where the wood will be located and how much preservative has been forced into it. Pressure-treated wood in contact with the ground needs the most protection, and will rot in just a few years if you use the wrong grade. If you’re planning a DIY project, make sure to tell your lumber dealer the end use, so you’ll get the right grade.

Grades of pressure-treated wood are numbered to indicate that amount of preservative per board foot. The grades start at .25 and go up to .60 (marine grade). If your wood will touch the ground or be buried, you should get the highest grade you can, up to .60 if it’s available. It will be more expensive, but you’ll save money in the long run by not having to replace it as often.