Lumber species and grade affect both strength and appearance of NLT. Color, uniformity of appearance, and presence of visual defects differ between species. In addition to aesthetic or structural considerations, species also vary in other important ways. Species absorb and release water at different rates, which should be considered if NLT will be exposed to significant moisture during construction. Workability and hardness also differ between species and generally relate to density; for instance, Douglas Fir is denser than SPF, which can result in more resistance when nailing or cutting, although only slightly.
Grade also matters where NLT is exposed as an interior finish. For instance, although visually graded No. 2 lumber may meet structural requirements, a higher appearance grade can minimize visual defects (wane, holes, large knots) to better address aesthetic criteria. Using Select Structural grade lumber will provide improved structural properties while reducing visual defects compared to No. 2 lumber, but availability may be limited, and Select Structural is typically more expensive. Although visually graded lumber is more common than Machine Stress Rated (MSR) lumber, MSR lumber can improve the strength and stiffness of NLT.
Where high-quality, exposed NLT is desired, fabricators ordering No. 2 and better material should expect to visually cull it for consistent quality and anticipate a typical waste factor of 15% to 20%. To assist with visual culling it may be helpful to identify visual characteristics of acceptable lumber in advance to facilitate a consistent look.
Some lumber mills offer specific appearance grades in addition to visual grading for structural performance. Request information on availability and differences between appearance grades from local lumber suppliers. Some higher appearance grades of lumber include Premium (or Prime) grade, Hi- Line (or Home Center) grade, and J Grade. J Grade is generally the highest quality of these options. A waste factor of 5% to 10% is typical for higher appearance grades, which may offset the increased cost of the lumber.
Other important considerations for selecting grade and species include fabrication efficiency and cost, such as labor required to grade and handle extra material, and space required to store additional material and culled lumber.
More on NLT
This is an overview to help become familiar with a versatile method of construction with a range of modern opportunity to create compelling architecture.