There are three Southern Pine lumber grading methods for sorting Southern Pine dimension lumber and assigning design values:
Visually Graded Lumber
This is the oldest and most common of the three methods. Qualified graders perform visual grading in the mill. These graders sort each piece of lumber into various grades based on visual characteristics known to affect lumber strength and stiffness, such as knot size and slope-of-grain.
Consistent visual grading is achieved through proper training, education, and supervision of lumber graders. Visually graded lumber will adequately meet the structural requirements for most traditional applications.
Machine Graded
This includes Machine Stress Rated (MSR) lumber and Machine Evaluated Lumber (MEL). Grade marks for MSR and MEL can include “1W” or “2W” if visually graded to the wane restrictions for No. 1 or No.2 visual grades, respectively. While each machine grading technique reduces the variability associated with assigning stress grades to lumber, there are slight differences between the two:
- Machine Stress Rated lumber is evaluated by mechanical stress rating equipment. MSR lumber is distinguished from visually graded lumber in that each piece is nondestructively tested and then sorted into bending strength and stiffness classes. Each piece of MSR lumber also must meet certain visual requirements before it can be assigned design values. MSR also requires daily quality control tests for bending strength and stiffness.
- Machine Evaluated Lumber is similar to MSR in that each piece is evaluated by nondestructive grading equipment, checked for visual requirements and then sorted into various strength classifications. MEL requires daily quality control tests for tension strength in addition to the daily bending strength and stiffness tests required for MSR.1W_mark_230x100
Availability
The Standard Grading Rules for Southern Pine Lumber provide for numerous visual, MSR, and MEL grades. However, not all of those possible grade/size combinations are produced or used in the marketplace.
Available grades and sizes are subject to change, so check sources of supply at the time of your project.
American Softwood Lumber Standard
The American Softwood Lumber Standard PS 20 of the U.S. Department of Commerce relates lumber size to moisture content. Separate size schedules for green and dry lumber ensure both products will approximate the same size in service. All bills and invoices are required to show actual net sizes of lumber.
Strength and stiffness values for Southern Pine products in current Southern Pine Inspection Bureau Grading Rules have been approved by the American Lumber Standard Committee’s Board of Review.
PS 20 provides for a National Grading Rule (NGR) for Dimension Lumber1 with simplified grade names and sizes to ensure uniformity, efficiency, and economy in the use of dimension lumber. The NGR was incorporated in the SPIB’s Standard Grading Rules for Southern Pine Lumber. Dimension lumber sizes and grades are:
Structural Light Framing:
- 2″ to 4″ thick, 2″ to 4″ wide
- Select Structural, No. 1, No. 2, No. 3
- Select Structural, No. 1 and No. 2 grades also include dense and non-dense options
Light Framing:
- 2″ to 4″ thick, 2″ to 4″ wide
- Construction, Standard, Utility
Studs:
- 2″ to 4″ thick, 2″ and wider
- Stud
Structural Joists & Planks:
- 2″ to 4″ thick, 5″ and wider
- Select Structural, No. 1, No. 2, No. 3
- Select Structural, No. 1 and No. 2 grades also include dense and non-dense options
1 NGR applies to dimension lumber and excludes items such as crossarms, factory and shop lumber, finish (selects), foundation lumber, industrial clears, ladder stock, laminating stock, railroad stock, rough lumber, scaffold planks, ship decking and plank stock, stadium plank, worked lumber, and special product rules for items such as radius edge decking, and prime and merchantable dimension.