NHLA Grading Standards Explained
The National Hardwood Lumber Association (NHLA) establishes the grading standards used throughout North America for hardwood lumber. These standards provide a consistent framework for evaluating lumber quality based on the percentage of clear, usable wood in each board.
FAS (Firsts and Seconds) represents the premium grade, requiring at least 83.3% clear face cuttings with minimum board dimensions of 6" wide by 8' long. This grade is ideal for projects where appearance and yield are critical, such as fine furniture and high-end cabinetry.
Select grade maintains the same 83.3% clear requirement as FAS but allows smaller minimum dimensions (4" wide by 6' long). This grade offers excellent quality while providing more flexibility for projects with smaller component sizes.
Common grades (#1, #2, and #3) accommodate increasing levels of character and defects. #1 Common requires 66.7% clear cuttings, #2 Common requires 50%, and #3 Common requires 33.3%. These grades offer cost-effective options for projects where some defects are acceptable or even desirable for rustic aesthetics.
Understanding Lumber Defects
Lumber defects significantly impact grading and must be carefully evaluated. Understanding these defects helps you select appropriate grades and anticipate yield from each board.
Knots are the most common defect, formed where branches grew from the trunk. Sound knots are tight and solid, while loose knots may fall out during processing. Pin knots (less than 1/4") have minimal impact, while large knots significantly reduce clear cutting yield.
Checks and splits are separations in the wood fiber. Checks are surface cracks that don't extend through the board, typically caused by uneven drying. Splits extend completely through the thickness and represent more serious defects that limit usable length.
Warp encompasses several distortion types: bow (lengthwise curve), cup (width-wise curve), twist (spiral distortion), and crook (edgewise curve). Severe warp can make boards unusable or require significant material removal during milling.
Sapwood is the lighter-colored outer layer of the tree. While structurally sound, sapwood is less durable than heartwood and may be considered a defect in some applications. Wane refers to bark or missing wood on board edges, reducing usable width and requiring additional trimming.
Selecting the Right Grade for Your Project
Choosing the appropriate lumber grade balances quality requirements against cost considerations. Understanding typical applications for each grade helps optimize your material budget.
FAS and Select grades are essential for fine furniture, high-end cabinetry, and any application where visible surfaces demand premium appearance. The higher cost is justified by superior yield and minimal waste in critical components like tabletops, cabinet doors, and drawer fronts.
#1 Common offers an excellent balance of quality and value for furniture parts, flooring, and millwork. This grade provides sufficient clear cuttings for most furniture components while costing significantly less than FAS. Many professional woodworkers prefer #1 Common for projects where some defects can be cut around.
#2 Common works well for rustic furniture, paneling, and shelving where character marks add visual interest. This grade requires more careful layout and cutting but can deliver beautiful results at a fraction of FAS pricing. It's ideal for projects embracing natural wood character.
#3 Common serves industrial applications like pallets and crates, or projects where appearance is secondary to function. While requiring significant cutting around defects, this grade can be economical for hidden structural components or shop fixtures.
Professional Grading Techniques
Accurate lumber grading requires understanding NHLA rules and developing a practiced eye for evaluating boards.
Always grade from the better face of the board, as NHLA standards base grades on the superior surface. This means a board with one excellent face and one poor face can still achieve a high grade.
Measure clear cuttings, not defects. The grading system focuses on usable wood area rather than defect area. Visualize how you would cut clear pieces from the board, ensuring each cutting meets minimum size requirements for that grade.
Account for minimum board dimensions specific to each grade. A board with excellent clear percentage may still not qualify for FAS if it doesn't meet the 6" × 8' minimum. Understanding these dimensional requirements prevents purchasing lumber that won't meet your grade needs.
Allow for end trimming—typically 1" from each end—to remove checking and splits common at board ends. This trimming is standard practice and should be factored into your yield calculations.
For F1F (First and Seconds One Face) grading, examine both faces even though only one needs to meet FAS standards. The reverse face must still meet #1 Common requirements, ensuring overall board quality.
Verify moisture content before grading, as NHLA standards assume lumber is properly dried to 6-8% MC. Wet lumber may appear to have fewer defects than it will after drying, when checks and other issues become more apparent.