Glulam Beam Basics
"Glulam beams are engineered wood products manufactured to meet a range of design stresses—but what exactly are they used for? Today, we're diving into the basics of glulams with Kristin Poyser, Marketing Development Manager at Rosboro, Washington & Alaska. "
We’ve all heard of "glulam beams" or "glulams,” but what exactly are they? What sizes do they come in, and where are they used? Today, we’re providing you with the basics on glulams, as provided by Kristin Poyser, Marketing Development Manager at Rosboro.
What is a glulam?
A glulam is manufactured from layers of wood laminations (“lams”) that are bonded together with industrial adhesives (glue). Hence the term glulam = glu + lam.
The grains of all the laminations in a timber run parallel along its length. The lumber used to create the lams is usually in a 1-3/8” thickness, or 1-1/2” thick lams made from a western species like Douglas fir in the western part of the country and southern yellow pine in the eastern part of the country (although other thicknesses may also be used). Rosboro is the largest full-width (3-1/2” & 5-1/2”) glulam manufacturer in North America.
Glulam products typically range in net widths from 2-½” to 10-¾”, but virtually any width can be custom made.
Because they are engineered wood products (EWP), glulam timbers are manufactured to meet a range of design stresses. Beams are manufactured with the strongest lams on the bottom and top of the beam, where maximum tension and compression stresses occur. This concept allows the lumber resource to be used more efficiently by placing higher-grade lumber in zones that have the maximum stresses and lumber with less structural strength in lower-stress parts of the beam.
Grades & uses of glulams
Sometimes glulams are strictly structural and looks are not a concern, but a glulam can also be simultaneously an architectural focal point as well as a structural timber. Because of this, there are different grades and appearance choices available:
- Architectural: With a smooth, attractive finish, an Architectural appearance glulam should be specified for applications where it will remain exposed to view. In this grade, you’ll find voids (holes and cracks) larger than 3/4" are filled. Low laminations are cosmetically repaired using inserts and wood fillers, corners of exposed wide faces are eased, and all exposed faces are sanded.
- Industrial: Available as a custom order, Industrial beams are intended for concealed applications where appearance is not particularly important. Holes, low laminations, and other surface defects are not to be filled, and narrow faces of the beam are not surfaced.
- Framing: This classification is intended only for use in concealed applications. Beams with this appearance classification are provided in widths designed to fit flush with common two-by-four and two-by-six wall framing. The Framing appearance standard allows for more irregularities than Architectural, since it is assumed the timber will not remain visible.
- Premium (industry specification): As the highest appearance classification, a Premium appearance glulam should be used when appearance is the primary design consideration. Laminations that minimize visible knot sizes are selected and all exposed surfaces are finished.
- Premium Hand Select: Rosboro can hand-select the lumber to reduce the size of knots and defects.
- Rough Sawn: This is another Appearance glulam that provides a timber-like texture.
All appearance classifications permit natural growth characteristics with varying degrees of open voids permitted. The appearance classification is not related to lumber layup requirements and thus does not affect design values for the beam.
Available sizes of glulams
Beams can be built to order based on the unique needs of a job, and can have a lead time as short as one week for those must-have orders. That said, there are standard sizes in dimensions such as:
- Widths of 3-1/2”, 5-1/2”, 6-3/4” and 8-3/4”
- Depths from 6” to 30” in 1-1/2” increments or I-joist compatible depths of 9-1/2”, 11-7/8”, 14” and 16”
- Depths to match 2 x 10” and 2 x 12” traditional framing are also available.
- Lengths to 50’ are generally always readily available and some beams are available up to 100 feet in length.
- Special order glulams are available with a three week lead time in widths of 10 ¾”, 12 ¼”, 14 ¼” and depths up to 48”.
- Glulam columns are available in 3-1/2 x 6”, 5-1/2” square, and 5-1/2” x 6” options.
Treated glulams
Treated Douglas fir glulams are also available. Waterborne treatments are not recommended. Due to the nature of the laminated beams and the adhesives used, there is generally not a written warranty for these timbers, so proper flashing and water management should be installed around them as best practice.
For someone wanting a naturally durable species of lumber without chemical treatment in their glulam, Alaska yellow cedar beams are available.
X-Beams and bending stress
X-Beams are the next generation of glulams with a specified, allowable bending stress for the beam. These stress ratings are achieved through precisely constructing the beam with varying grades and/or species of high quality lumber ordered in specific layers. An example of a stress rating is 24F, meaning the allowable bending stress is 2400psi.
X-Beams & Big Beams
High-strength rated specialty types of glulams are X-Beams and Big Beams. Rosboro’s X-Beam™ is an Architectural appearance beam that matches standard framing lumber dimensions, so they intersect seamlessly using standard metal hangers and fasteners. A common use is door and window headers. Since X-Beams are designed with appearance in mind, they can be left open and visible, or concealed.
The Big Beam DF™ from Rosboro is a great choice for a concealed high-strength engineered beam or header application. As with the X-Beams, the full 3 1/2" and 5 1/2" width match standard framing dimensions and depths are available to match standard I-joists too.
Big Beam DF™ offers the following features:
- Easy to cut and install
- Balanced layup (no specific top or bottom to beam)
- Ideal for wall and floor framing
- I-joist depths are compatible with other EWP floor systems
- Dry, straight, dimensionally stable
- No special hangers or screws required
Big Beams come in the following dimensions:
- Widths: 3-1/2”, 5-1/2” and 7”
- Depths: 9-1/4”, 9-1/2”, 11-1/4”, 11-7/8”, 14”, 16” and 18”
- The full 3-1/2” and 5-1/2” widths make Big Beams and X-Beams ideal for wall framing.
Need detailed information?
Rosboro makes these and other laminated structural beams designed for many applications. To access detailed information including camber charts and more, visit their very informative online Resource Library.
Camber in glulams
The ability to order pre-cambered glulams is a great advantage for longer span applications. Most stock beams are used in residential construction in combination with standard framing, and a camber can cause problems if not accounted for. Therefore, stock beams are typically supplied with zero camber or camber that amounts to only ¼” in a 28-foot run (virtually unnoticeable). The "zero camber" allows for easy compatibility with non-cambered framing members.
Notching or cutting holes in glulams
When a glulam is used, it’s often because the timber is needed for a specific span, camber, or tension specification. Notching or drilling can compromise the integrity and required strength of the beam since those modifications alter the laminations and specific lay up of the engineered beam. In certain cases, it may be fine to alter the member in this way. We can’t possibly address every scenario in this article, so let’s look at the basics:
Notching
Avoid notching whenever possible – especially on the tension side of a member. Notching on the compression side may be less of an issue and probably requires less in the way of extra measures. Either way, consultation with an engineer is absolutely recommended so as not to weaken the member and create a liability.
Drilling
As with notching, drilling is generally not recommended because it can lower the capacity of the laminated beam. That said, available drilling charts will give you guidelines for where in the beam one can locate small diameter access holes.
Small penetrations can be made in specific parts of a beam to allow passage of plumbing, wiring, conduit, and other small, lightweight equipment. Note that these holes allow something to pass through. Drilling holes in order to mount a bracket (or anything load-bearing) is never recommended unless specifically called for by a design engineer.
Notes:
Charts that show allowable notching and drilling are available from the glulam manufacturer.
Glulam beams often come sealed with a protective coating. Notching or drilling compromises that coating and can change the rate of moisture absorption. This can lead to splitting. If an allowable notch or penetration is made in the glulam member, it should be sealed immediately with a water-repellent sealer.
X-Beam Columns
While glulams are generally pictured in horizontal (beam) applications, laminated columns are available as well and provide these advantages:
- Very high compression strength
- Architectural appearance
- Framing can run from floor to ceiling with one continuous piece
- Same column material can be used for the horizontal framing in tall wall construction
We hope this article has both taken some of the mystery out of glulams as well as shown you the multitude of uses they lend themselves to. From standard to appearance grades to stress-rated beams for specific spans, Rosboro and Dunn Lumber can provide virtually any laminated timber you need.
