What Are Glulams and How They Are Used
Glulam is short for glue-laminated timber. It is a versatile and innovative construction material used widely in both commercial and residential projects. Glulam is made with multiple layers of solid-wood lumber bonded together with high-strength adhesive to form a single structural unit. Builders often refer to glulam beams and other members simply as "glulams."
What Is Glulam?
Glue-laminated timber is an engineered wood product, meaning it is made from wood but is machined and assembled to precise specifications to create a predictable, dimensionally stable material. Other common engineered wood products include plywood, oriented strandboard (OSB), and laminated veneer lumber (LVL). A glulam beam looks like a stack of 2x4s (or larger lumber) glued together on their broadsides. This is in contrast to other engineered members, such as LVL and Microlam beams, which have very thin layers of wood glued side by side and look like thick plywood.
Glulam members are sold in several standard widths and lengths and can be custom-fabricated to meet almost any design specifications. They are commonly used for large curved or arching members to build vaulted roofs, domes, and even bridges. Glulam offers superior strength and stiffness over dimensional lumber and it is stronger than steel, pound for pound. Connections for glulams are typically made with bolts or steel dowels and steel plates.
Common Uses of Glulams
Glulam members can be used in a wide variety of applications and for both indoor and outdoor projects. Common forms of glulam members include:
- Straight beams, including lintels, purlins, ridge beams, and floor beams
- Columns, including round, square, and complex sections
- Tied rafters
- Tied arches
- Arched bridge supports
- Curved beams
Glulam Strength Classification
Glulam members are classified by specific strength properties and are given a rating from a Stress Classification System. The first part of the rating is the reference bending design value, or its flexural loading. For example, a 24F signifies that the member has 2,400 pounds per square inch (psi) of flexural loading. The second part of the rating is the corresponding modulus of elasticity value of the glulam member. For example, a 24F-1.8E indicates a reference bending design value of 2,400 psi and a modulus of elasticity of 1.8 x 10^6 psi.
Glulam material comes in four different appearance grades, as listed in American National Standards Institute (ANSI) A190.1 (2002):
- Framing. Framing appearance grade is the common choice for homebuilding and other areas where glulam is specified and will be combined with dimension lumber. This grade is recommended only for use in concealed areas.
- Industrial. Industrial-grade appearance for glulam material is recommended for areas where the aesthetics are not a major concern. Under this appearance grade, the glulam is finished slightly better than with the Framing grade, but it is not an aesthetic product. It should be used in areas not visible to general public. This appearance grade will show some wood imperfection on its surfaces, such as knots and voids.
- Architectural. When glulam is going to be used as a facade material or exposed element, Architectural-grade appearance is highly recommended. This grade offers a high-quality finished product, where wooden voids and imperfections are filled or treated to provide a smoother, more attractive surface.
- Premium. This grade of glulam is available only through special order and usually is reserved for special situations or pre-determined areas, where a high concentration of people is expected. Premium-grade glulam offers the smoothest surfaces for the highest-quality finished product.
Why Use Glulam?
Glulams are not only strong, cost-effective, and highly customizable; they're also resource-efficient because they are made with relatively small pieces of lumber to create a sizable wood member that you could only otherwise get from large, old-growth timber. Glulams offer many benefits to designers and builders:
- Versatile use as roof and floor beams, columns, bracing, decking, and other structural components
- Eco-friendly material with very low formaldehyde levels
- Capable of creating unsupported spans of over 500 feet
- Reduced transportation and handling costs
- Easy installation and surface repair
- Customizable to fit special needs
- Standard sizes available immediately
- Produced in well-managed forests and certified to PEFC standards
- Good fire-resistance; can outlast steel beams under the same fire conditions
- Manufactured to precise dimensions
Handling and Storage Tips
Glulam members should be handled carefully to prevent any damage or reduction in their structural capacity. It is recommended that fabric slings be used when lifting to prevent surface scratches. Members should be stored vertically, if possible, and always should be protected from the weather by a covering of plastic sheeting. Unless glulam material is intended for exposed areas, it should be protected from outdoor exposure until it is ready to be installed.