Grades of Dimensional Lumber & Decking
Different projects require different types of pressure-treated lumber. Lumber mills ink-stamp each board with a lumber grade. Grades refer to the quality, strength and appearance of the wood.
#1 Grade Lumber
Use when both strength & appearance are important.
- Boards contain small and few knots
- Knots may be no larger than 2 ¾"
- One hole is permitted every 3 feet
- No splits larger than the width of the board
- Stronger than #2 grade because it has fewer and smaller knots
#2 Grade Lumber
Use when appearance is not important.
- Grain slope must meet a minimum 1/8-grain slope (the less deviation from straight grain parallel to the edge, the stronger the piece of lumber).
- Boards contain splits no larger than 1.5 times width of board
- Knots may not be larger than 3 1/2"
- One hole is permitted every 2 feet
- May have wane (bark edge) on corners
- More knots and bark edges than #1 grade
Prime Grade Lumber
Use when appearance is important.
- Prime grade lumber provides the same structural properties as #1 grade lumber, but has fewer knots and better appearance
- #2 Prime grade has the strength of #2 grade lumber, but will look better, with fewer knots
Radius Edge Decking
5/4" wood decking is graded for both strength and appearance and is available in Premium and Standard grades.
Use when small knots are desired and appearance is very important.
- Best appearance (compared to Standard)
- High-quality lumber
- Smaller and fewer knots
Use when a rustic appearance is desired.
- More knots than Premium grade
- Knots may be larger
- Treated wood is typically still wet when it’s delivered to the lumberyard 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.
- Most lumber and building materials dealers stock only a few grades of lumber but usually allow customers to special-order non-stocked grades of lumber.