Some treated lumber contains a wax coating in addition to the insect-resistant chemicals. Most lumber manufacturers recommend reapplying a sealant at least every other year. Cedar or redwood lumber costs more than treated wood. Cedar typically costs 25 percent more than treated, and redwood can be up to 50 percent more than treated wood, Nettleton said. Lumber is classified in many grades, which primarily affect its aesthetics rather than structural capacity.
Sawmills inspect lumber and stamp it before it hits each lumberyard.
Practically any piece of lumber will have some degree of defect. Boards can contain knots, which are the remnants of tree limbs, splits and wanes. Wanes are pieces of bark still on the board or rough areas along an edge that isn't square. Because No. 1 grade lumber will cost more, it's usually only necessary if the look of the wood is important. When sorting through grade classifications, don't forget that the nominal lumber measurements differ from actual dimensions.