Laminated veneer lumber (LVL) and glued laminated timber (glulam) are engineered wood products designed to carry substantial design loads in structural applications. Unlike solid sawn lumber, these members are manufactured with specific stress-rated laminations that make field modifications such as notching, tapering, and drilling particularly consequential. When such modifications are required and not shown on approved construction documents, building professionals must follow strict engineering guidelines to avoid compromising structural integrity. This article presents the essential field notching and drilling requirements for LVL and glulam beams, based on technical guidance from the Engineered Wood Association. For broader context on how these materials fit into modern wood construction, see our coverage of scalable timber engineering for LVL and CLT mass timber systems.
Understanding LVL and Glulam Beam Construction
Glulam beams are manufactured by bonding multiple layers of dimension lumber with structural adhesives. The laminations are arranged so that higher-grade material occupies the outermost positions, particularly on the tension side, while lower-grade material is placed near the neutral axis at mid-depth. This engineered grading strategy means that any field modification removing wood fiber from the tension-side laminations directly affects the beam strength capacity in two ways: it reduces the gross cross-section and it removes the highest-strength wood fiber from the most critical stress zones. Stress concentrations at notched or drilled locations further compound these effects.
LVL products are manufactured by bonding thin wood veneers together with the grain oriented parallel to the member length. Most LVL beams and headers are loaded parallel to the glue lines. Like glulam, LVL is a proprietary product, and the field modification requirements specified by each LVL manufacturer take precedence over general recommendations. Both material types share a fundamental principle: improperly executed field modifications can reduce the capacity of a properly designed member and potentially cause structural deficiency.
Field Notching Requirements for Glulam and LVL Beams
Notching of bending members should be avoided whenever possible, especially on the tension side. All recommendations assume simple-span beams with uniform loading and the top side in compression. Continuous and cantilevered beams require more conservative approaches and rational engineering analysis.
Tension-Side Notching Restrictions
Tension-side notching of glulam beams is not permitted except at end bearings and only under specific conditions. The same restriction applies to LVL beams. When a notch is made on the tension side, it induces perpendicular-to-grain tension stresses that, in combination with horizontal shear forces, can cause splitting along the grain typically starting at the inside corner of the notch. To mitigate stress concentrations:
- Use a gradually tapered notch configuration instead of a square-cornered notch whenever possible.
- Round the square corner of any notch with a radius of approximately 13 mm (0.5 in.) to reduce stress concentrations.
- For square-cornered notches at beam ends on the tension side, consider using full-threaded lag screws as reinforcement to resist splitting at the notch.
- Predrill lead holes for any lag screw installation in accordance with accepted practice.
- Drill a pilot hole at the interior corner location of a notch as a stopping point for the saw blade to prevent over-cutting and provide a rounded corner.
Where glulam or LVL members are notched at the ends for bearing over a support, the notch depth must not exceed one-tenth of the beam depth. The equations for evaluating the associated shear strength reductions at end notches are empirical in nature. For notches on the compression side, a less severe condition exists, but analysis equations still apply.
Compression-Side Notching Provisions
When a small notch is needed in the top of a beam in the compression zone to provide passage for small-diameter pipe or conduit, the cut must be made in areas stressed to less than 50 percent of the design bending stress. The net section must be checked for both shear and bending stresses. The design equations for compression-side notches are shear equations because these notches typically occur in regions of high shear and effectively zero moment. When compression-side notches extend into areas of significant moment, the bending capacity of the beam must also be checked using the remaining section and appropriate allowable stresses.
For LVL beams specifically, one important consideration applies: the top of the beam may not always be in compression and the bottom may not always be in tension. When the beam is designed for wind uplift, the stress orientations reverse, and the notching recommendations must be applied accordingly. Additionally, when evaluating notch effects on LVL, the shear force within a distance from supports equal to the beam depth must not be neglected, unlike the typical allowance for rectangular wood members under the National Design Specification for Wood Construction.
Drilling Guidelines for Engineered Wood Members
Horizontal and vertical holes in engineered wood members remove wood fiber, reduce net area, and introduce stress concentrations. The size, location, and spacing of field-drilled holes must be strictly controlled to maintain structural integrity. Field-drilled horizontal holes should be used for access only and not as attachment points for brackets or load-bearing hardware unless specifically designed for such purposes. For additional context on how these wood products perform in larger assemblies, see our coverage of glulam performance in mass timber construction.
Horizontal Hole Size and Location
For glulam beams, field-drilled horizontal holes must comply with these requirements:
- Hole size: The hole diameter must not exceed 38 mm (1.5 in.) or one-tenth of the beam depth, whichever is smaller.
- Edge distance: A minimum clear distance of four hole diameters to the top or bottom face and eight hole diameters from the beam end.
- Spacing: Minimum clear spacing between adjacent holes must be eight hole diameters based on the largest adjacent hole.
- Quantity: Maximum of one hole per 1.5 m (5 ft) of beam length. For a 6.1 m (20 ft) beam, this means a maximum of four holes.
A 25 mm (1 in.) diameter or smaller hole may be drilled at the middle half of the beam depth anywhere along the span, except within 152 mm (6 in.) of the support, provided the beam is at least 184 mm (7.25 in.) deep, subject to uniform loads only, has a span-to-depth ratio of at least 10, and the hole is not in a cantilever. For LVL beams, the same small-hole rule applies with a span-to-depth ratio requirement of at least 11, a maximum of three holes per span, a minimum horizontal spacing of two diameters, and the hole zone restricted to the middle third of the beam depth rather than the middle half.
Vertical Hole and Equipment Support Considerations
Vertical holes drilled through the depth of a beam should be avoided whenever possible. The capacity reduction at the hole location is directly proportional to the ratio of 1.5 times the hole diameter to the beam width. For example, a 25 mm (1 in.) hole drilled in a 152 mm (6 in.) wide beam reduces the capacity by approximately 25 percent. When vertical holes are necessary, they must be positioned in areas stressed to less than 50 percent of design bending stress. The minimum clear edge distance from either side of the member to the nearest edge of the vertical hole must be 2.5 times the hole diameter. For LVL, the beam width must be at least 89 mm (3.5 in.) before any vertical drilling is considered, and an engineer must be consulted prior to drilling.
Heavy equipment or piping suspended from beams must be attached so the load is applied to the top of the member to avoid tension perpendicular-to-grain stresses. Any horizontal holes required for supporting significant weight must be located above the neutral axis and in a zone stressed to less than 50 percent of the design flexural stress. Fasteners supporting light loads, such as light fixtures, must be placed at least four laminations or 25 percent of beam depth, whichever is greater, away from the tension face. Keep up with wood construction standards and industry guidance from organizations like the American Wood Council for evolving best practices in engineered wood design.
| Parameter | Glulam Requirement | LVL Requirement |
|---|---|---|
| Maximum hole diameter | 38 mm (1.5 in.) or d/10, whichever is smaller | Per manufacturer specifications |
| Minimum beam depth for small holes | 184 mm (7.25 in.) | 184 mm (7.25 in.) |
| Minimum span-to-depth (l/d) ratio | 10 | 11 |
| Maximum holes per span | 1 per 1.5 m (5 ft) of length | 3 per span |
| Small hole zone (25 mm diameter) | Middle half of beam depth | Middle third of beam depth |
| Clear distance from support | 152 mm (6 in.) | 152 mm (6 in.) |
| Horizontal hole spacing | 8 diameters clear | 2 diameters clear |
| Min beam width for vertical holes | No specific minimum | 89 mm (3.5 in.) |
Protection, Sealing, and Quality Assurance
An often-overlooked aspect of field modifications is the protection of cut surfaces. LVL and glulam beams are typically shipped from the manufacturer with end-grain sealers that retard moisture migration. When a notch is cut in the field, the protective coating is broken, changing the moisture-absorption characteristics at that location. This can lead to seasoning checks and localized splitting at the root of the notch.
To minimize this risk, follow these protection procedures:
- Seal all field notches immediately after cutting using a water-repellent sealer.
- Apply sealer to all field-cut locations, including the interior surfaces of drilled holes.
- Use a brush, swab, roller, or spray gun for application.
- Inspect sealed surfaces periodically during construction to ensure the coating remains intact.
- Recoat any surfaces that are damaged or exposed during subsequent construction activities.
Regardless of hole location, all holes drilled horizontally through a member must be positioned and sized with the understanding that the beam will deflect over time under in-service loading conditions. This deflection could cause distress to supported equipment or piping unless properly considered. A drill guide should be used for all vertical drilling to minimize bit wandering through knots and varying-density material and to ensure true alignment through the beam depth.
Additional engineering guidance for non-standard applications is available from APA technical notes, including Form V700 for large-diameter horizontal holes in glulam and Form V900 for large-diameter holes in LVL. These resources provide design methodologies for situations where standard prescriptive guidelines cannot be met. All field modifications should ultimately be reviewed and approved by an engineer of record competent in timber design. For broader context on how engineered wood products are reshaping construction, see our coverage of mass timber building code developments and their implications for structural design using LVL and glulam members.