NOTE This Standard covers structural glued-laminated timber (glulam) furnished as primary framing, including horizontal beams and girders, vertical columns, and curved or shaped members such as arches, Tudor frames, and pitched or tapered members. (1.1)

NOTE Glulam is an engineered wood product built from individual dimension-lumber laminations bonded face-to-face with a structural adhesive, with the highest-strength laminations positioned where bending stress is greatest. Because the layup, stress class, and shape are all controlled at the mill, glulam is specified by its engineered properties rather than by a nominal lumber size, and it must be manufactured and certified under a recognized product standard before it can be used as code-conforming structural framing. (1.2)

NOTE Cross-laminated timber (CLT) panels are outside this Standard and are governed by Mass Timber. (1.5)

NOTE Dimension-lumber stud, joist, and rafter framing, laminated veneer lumber (LVL) headers, and prefabricated wood I-joists are outside this Standard and are governed by Wood Framing. (1.6)

NOTE Rough framing, blocking, nailers, and ungraded dimensional lumber are outside this Standard and are governed by Rough Carpentry. (1.7)

NOTE Pre-engineered wood roof trusses using dimensional lumber or metal-plate connectors are outside this Standard and are governed by Wood Roof Trusses. (1.8)

NOTE Column-base foundations, anchor-bolt layout, and base-plate bedding are coordinated with Shallow Foundations and Non Shrink Grout; this Standard governs only the glulam member and its bearing hardware. (1.9)

NOTE The 2021 IBC references ANSI A190.1 as the required manufacturing standard for glulam, and NDS Chapter 5 governs the structural design of glulam members; the edition of each standard adopted by the authority having jurisdiction governs, and the Contractor shall verify local adoption before procurement. (2.3)

NOTE APA is the secretariat for ANSI A190.1 and the dominant third-party certifier; AITC technical notes such as AITC 104 remain active industry references for detailing even though independent AITC certification has been consolidated into APA's program. The Contractor shall confirm that the proposed certification agency is acceptable under the contract before procurement. (4.4)

NOTE The mill shall mark the top (compression) face of every bending member so that camber orientation can be verified in the field before the member is connected. (4.7)

NOTE Stress Class and Combination (5.1)

NOTE Glulam bending members are specified either by stress class — a designation such as 24F-1.8E that pairs an allowable bending stress (24F = 2,400 psi) with a modulus of elasticity (1.8E = 1.8 million psi) — or by a full combination such as 24F-V8 (visually graded) or 24F-E2 (E-rated lamination). Specifying by stress class lets the manufacturer select an equivalent layup from available stock or species, which usually shortens lead time; specifying a full combination locks in one layup and is reserved for cases where a particular lamination arrangement is structurally required. (5.1.1)

NOTE Where a specific combination is required, the combination designation shall be stated on the structural drawings and reproduced on the shop drawings. (5.1.4)

NOTE Species (5.2)

NOTE Glulam design values depend on the laminating species, so the species shall be identified whenever regional sourcing affects the structural engineer's calculations. Douglas-fir/larch is the common Western species, Southern yellow pine (SYP) is standard in the Southeast, and Hem-fir and custom species mixes are available; SYP and Douglas-fir carry different allowable values and are not interchangeable without recalculation. (5.2.1)

NOTE Layup Orientation — Balanced and Unbalanced (5.3)

NOTE An unbalanced layup places higher-grade laminations on the tension face and is used for simply-supported single-span beams; a balanced layup is symmetric about mid-depth and is required for continuous spans, cantilevers, and any member that could be installed reversed in service. Selecting an unbalanced layup and then installing it with the wrong face in tension can sharply reduce the allowable bending stress, so the orientation must be designated explicitly. (5.3.1)

NOTE Appearance Grade (5.4)

NOTE Appearance grade controls only the cosmetic finish of the exposed surfaces and has no effect on structural design values. Framing grade is utilitarian and intended for concealed members; Industrial grade is for members exposed in non-architectural settings; Architectural grade is for members exposed in finished interiors; and Premium grade is the highest cosmetic standard. Architectural and Premium grades cost roughly 15 to 25 percent more than Framing grade, so specifying them for concealed members adds cost with no structural benefit. (5.4.1)

NOTE Cross-Section (5.5)

NOTE Glulam is produced in standard net widths and in depth increments of one lamination, so cross-sections are most economical when they use standard dimensions; non-standard widths are a custom order and add cost and lead time. The standard width and depth fields below let the engineer fix the member size, and the section may be deferred to the structural drawings where it varies by member. (5.5.1)

NOTE Member depth is built up in 1-1/2 in lamination increments; the depth specified shall be a whole multiple of the lamination thickness. (5.5.3)

NOTE Camber (5.6)

NOTE Camber is a built-in upward curvature that offsets dead-load deflection so a member appears level under sustained load. Roof beams are conventionally cambered at 1.5 times the calculated dead-load deflection to also shed water and avoid ponding, floor beams at 1.0 times dead-load deflection, and short spans under about 20 ft are often left flat. Camber is specified as a mid-span rise or a radius of curvature, and the direction matters: a member installed upside-down deflects in the wrong direction and its net deflection roughly doubles. (5.6.1)

NOTE Design Adjustment Factors (5.7)

NOTE NDS design of glulam applies several adjustment factors to the tabulated values, and two are commonly overlooked. The volume factor CV reduces allowable bending stress for members deeper than the 21 in reference depth or longer than the 12 ft reference span, and can lower allowable Fb by 10 to 30 percent on large beams; designers used to sawn lumber sometimes skip it. The wet-service factor CM reduces all tabulated values when the in-service moisture content exceeds 16 percent, and the temperature factor Ct applies in sustained elevated-temperature service. (5.7.1)

NOTE Glulam moves with seasonal changes in moisture, and most service problems trace back to either too much moisture reaching the wood or restraint that prevents the member from shrinking freely. The service condition — interior dry, protected exterior, or wet/ground contact — drives the moisture-content limit, the adhesive type, and whether preservative treatment is required. (6.1)

NOTE Glulam used in exposed, exterior, or high-humidity conditions shall be preservative-treated in accordance with AWPA U1, and the Use Category shall be specified. Use Category UC3B covers material exposed above grade, and UC4B covers ground contact; the retention required rises with the category. (7.1)

NOTE Copper-based preservatives are highly corrosive to standard zinc-plated steel, so connectors and fasteners in treated members must be upgraded. (7.5)

NOTE Glulam connection detailing has to respect two facts about wood: it shrinks and swells across the grain with moisture, and its end grain wicks water. Detailing that ignores either one will split the member or rot the bearing over time, regardless of how strong the steelwork is. AITC 104 is the industry reference for typical bearing, base, ridge, and hanger details. (8.1)

NOTE Cross-Grain Restraint (8.3)

NOTE Wood shrinks across the grain as it dries but barely along the grain, so a connection that fixes the member at two points spaced vertically through the depth restrains that cross-grain movement and can split the member as it seasons. A full-depth vertical row of tight bolt holes is the classic cause of seasonal splitting. (8.3.1)

NOTE Bearing and Moisture Standoff (8.4)

NOTE End grain bearing directly on concrete or masonry wicks moisture into the member and causes checking and decay at the very point carrying load. (8.4.1)

NOTE Connection Hardware (8.5)

NOTE Hangers, saddles, base anchors, and other connection hardware shall be specified to suit the member size and the service condition, and the hardware corrosion grade shall match the exposure and any preservative treatment. (8.5.1)

NOTE Fabricated members shall comply with the dimensional tolerances of ANSI A190.1. (9.1)

NOTE Curved glulam — arches, Tudor frames, A-frames, and pitched or tapered members — is a custom-fabricated product built by bending laminations to a radius before cure. Tighter radii require thinner laminations, and radii as tight as about 7 ft are achievable. Curved and large-section members carry longer lead times than stock beams, which must be reflected in the procurement schedule. (10.1)

NOTE Stock straight beams in common Douglas-fir or SYP stress classes are available from distributor inventory in standard widths and depths, typically to 36 in deep and 40 ft long, on short notice. Custom-length, large-section, curved, and preservative-treated members are fabricated to order with lead times on the order of 4 to 8 weeks. Custom connection hardware can carry its own long lead, so glulam and its hardware must be released for fabrication concurrently to protect the schedule. (11.1)

NOTE Glulam arrives from the mill at a controlled moisture content and, for exposed grades, with a protective wrap; careless storage on site can undo both. Members must be kept off the ground, kept dry, protected from sun and weather, and handled at marked lift points so the surfaces and the camber are not damaged before erection. (12.1)

NOTE End grain absorbs moisture far faster than face grain, so any field cut opens a fresh moisture path that leads to checking, splitting, and decay if it is not sealed quickly. Factory end-sealing protects the as-fabricated member; the field has to re-seal every cut, promptly. (13.1)

NOTE Exposed glulam in finished spaces is both structure and architectural finish, so its appearance is protected through erection and any specified field finish is applied per the manufacturer's instructions. (15.1)

NOTE Because glulam members are engineered and custom-marked, a damaged member generally cannot be replaced from stock; replacement requires re-fabrication to the original shop drawings. Retaining the approved shop drawings and mill certifications makes future replacement or evaluation possible. (17.1)