Model building codes recognize finger-jointed lumber for the same structural applications as solid sawn lumber with certain qualifications.
AWC’s code adopted National Design Specification® (NDS®) for Wood Construction, which specifies finger jointed lumber as having the same design values as solid sawn lumber.
From Chapter 4 of the 2005 NDS:
22.214.171.124 When the reference design values specified in the NDS are used, the lumber, including end-jointed or edge-glues lumber, shall be identified by the grade mark of, or certificate of inspection issued by, a lumber grading or inspection bureau or agency recognized as being competent (see Reference 31). A distinct grade mark of a recognized lumber grading or inspection bureau or agency, indicating that joint integrity is subject to qualification and quality control, shall be applied to glued lumber products.
4.1.6 Reference design values for sawn lumber are applicable to structural end-jointed or edge-glued lumber of the same species and grade. Such use shall include, but not be limited to light framing, studs, joists, planks, and decking. When finger jointed lumber is marked “STUD USE ONLY” or “VERTICAL USE ONLY” such lumber shall be limited to use where any bending or tension stresses are of short duration.
The NDS is referenced in all major model building codes in the U.S.
To obtain a copy of the NDS, which is part of the 2005 Wood Design Package, call the AWC publications department at 1-800-890-7732 or visit the website.
End-joined lumber can be manufactured in different ways. Finger-joints or butt-joints are typical methods of joinery. The standards under which finger-jointed lumber is manufactured are the grading rules for end-joined pieces. These grade rules are promulgated like any other lumber grade rule and are ultimately reviewed by and approved by the American Lumber Standard Committee (ALSC). Finger joints for use in structural applications bear the grade stamp of an agency certified and approved by the Board of Review of ALSC.
ALSC recently modified its Glued Lumber Policy to add elevated-temperature adhesive performance requirements for end-jointed lumber intended for use in fire resistance-rated assemblies. End-jointed lumber manufactured with an adhesive which meets these new requirements is being designated as “Heat Resistant Adhesive” or “HRA” on the grade stamp. End-jointed lumber manufactured with an adhesive not tested or not qualified as a Heat Resistant Adhesive will be designated as “Non-Heat Resistant Adhesive” or “non-HRA” on the grade stamp, and will continue to meet building code requirements when used in unrated construction.
Adhesives used in finger-jointed lumber are of two basic types, depending on whether they are to be used for members with long duration bending loads like floor joists or short duration bending and tension loads like wall studs. Wood products using both types of adhesives have undergone extensive testing by manufacturers. Glued connections in products using the first adhesive type, containing phenolic resins, are sometimes referred to as “Structural Finger Joint,” and typically can be found in structural panels and glued-laminated timber. These products may be used interchangeably with solid sawn lumber in terms of strength and end use, including vertical or horizontal load applications. The second type of adhesive, typically containing polyvinyl compounds, is used with products that are then marked “VERTICAL USE ONLY” or “STUD USE ONLY.” These wood products may be used interchangeably with solid sawn lumber in terms of strength and are intended for applications where bending and tension stresses are of short duration, such as typically found in stud walls.