A glulam beam is a structural wood beam made by gluing many layers of dimension lumber together face to face, with the grain of every layer running along the length of the beam. Glulam (short for glued laminated timber) is used for long spans and exposed beams in houses, churches, gyms and timber-frame buildings, and it can be made straight, curved or tapered.
This guide covers how glulam is built, the stock sizes, what the layup codes and appearance grades mean, how camber works, and when glulam makes more sense than steel or other engineered wood. Figures were checked against APA and American Wood Council publications on October 31, 2026.
How a Glulam Beam Is Made
Kiln-dried boards, usually 2x lumber, are graded, finger-jointed end to end into long laminations, coated with structural adhesive and clamped into a stack. After curing, the sides are planed to the final width. Because the beam is assembled from many boards, a knot in one lamination is surrounded by clear wood in the others, and the manufacturer can put the strongest boards where the stresses are highest.
APA’s glulam overview states that APA-trademarked glulam is manufactured to ANSI A190.1, the product standard for structural glued laminated timber (the 2022 edition is current), and that glulam is recognized by the major model building codes. Look for the APA or other agency trademark stamped on the beam: it tells the inspector the grade, species and standard.
Stock Glulam Beam Sizes
Glulam comes in two broad groups: stock beams that lumber yards keep on hand for houses, and custom members made to order for larger buildings. APA lists stock beam widths and depths as follows:
| Stock width | Typical use |
|---|---|
| 3-1/8 in | Fits within a 2×4 wall |
| 3-1/2 in | Matches 2×4 framing width exactly |
| 5-1/8 in | Fits within a 2×6 wall |
| 5-1/2 in | Matches 2×6 framing width exactly |
| 6-3/4 in | Heavier headers and girders |
Stock depths run from 6 to 36 inches, according to the same APA page. The 3-1/2 and 5-1/2 inch widths are sized to sit flush with 2×4 and 2×6 walls, while the 3-1/8 and 5-1/8 inch widths are slightly narrower. Some yards stock beams in depths that match wood I-joists, so a glulam header or girder can sit flush with the floor; our wood I-joist size chart lists those joist depths. Availability varies by region, so confirm with a supplier before designing around a size.
Layup Codes: What 24F-V4 Means
Every glulam beam carries a combination symbol that tells the designer its strength class and how it was assembled. Using APA’s explanation:
- The number and F (such as 24F) give the bending stress class, here 2,400 psi allowable bending stress for the stress class.
- V or E tells you how the lumber was graded: V for visually graded, E for mechanically (E-rated) graded.
- The final number identifies the specific lamination combination.
APA gives 24F-V4 as the example: an unbalanced layup of visually graded Douglas fir with a full set of assigned design stresses. Unbalanced beams have stronger laminations on the tension side, are intended for simple spans and are stamped “TOP”. Install one upside down and it loses a large part of its capacity. Balanced layups have the same grades top and bottom and are used for continuous spans and cantilevers, where the bending reverses over a support.
Appearance Grades
Glulam has four appearance classes. APA notes that appearance class does not change the structural design values; it only controls how the surface looks.
| Appearance class | Where it is used |
|---|---|
| Framing | Concealed in walls, floors and ceilings |
| Industrial | Concealed, or exposed where looks do not matter (warehouses, garages) |
| Architectural | Exposed beams with a smooth finished surface |
| Premium | Custom order where appearance is the top priority |
Camber: Why Some Glulam Beams Are Curved
Glulam can be built with a slight upward curve, called camber, so that the beam settles to roughly level once it carries its permanent load. APA’s overview says roof beams are typically cambered at 1.5 times the calculated dead load deflection and floor beams at 1.0 times, and that stock beams usually have a 5,000 ft radius camber or none at all. Camber also helps flat roofs drain instead of ponding.
Camber has to be installed crown up. If a stock cambered beam is used as a short header in a wall, the small curve is usually not a problem, but under a flat finished ceiling a 5,000 ft radius can be visible over a long span. APA’s Glulam Product Guide (Form X440, revised June 2023) covers specification, storage, handling and installation in more detail.
Glulam vs Steel vs Other Engineered Wood
| Beam type | Made from | Strengths | Watch out for |
|---|---|---|---|
| Glulam | Dimension lumber glued face to face | Long spans, curved shapes, attractive when exposed, wide stock widths | Heavier and deeper than steel for the same load; “TOP” orientation |
| LVL | Thin veneers glued together | Consistent, built up from 1-3/4 in plies, easy to carry in | Plain look, normally kept concealed |
| Flitch beam | Steel plate bolted between wood members | Stiffer than wood alone at the same depth | Many through-bolts; heavy plate |
| Steel wide flange | Hot-rolled steel | Shallowest depth for a given load and span | Needs fabrication, fire protection where required, wood nailers to attach framing |
Steel’s advantage is depth. Structural steel has a modulus of elasticity of 29,000 ksi, far higher than any wood product, so where headroom is tight a steel beam usually carries the same load in less depth. For typical steel sizes and spans, see the steel beam span chart. Glulam wins where the beam stays visible, where the span is long but depth is available, or where a curved or tapered shape is wanted.
Where Glulam Beams Are Used
- Ridge beams in vaulted and cathedral ceilings, often left exposed. Our article on ridge beam vs ridge board explains when a structural ridge is required.
- Garage door and wide window headers, where a single piece replaces built-up lumber.
- Basement girders carrying floor joists to posts. See our basement support beam guide for the alternatives.
- Deck and porch beams, but only if the glulam is treated or a naturally durable species (see below).
- Arches and long-span roofs in churches, gyms and arenas, using custom curved members.
Using Glulam Outdoors
Standard glulam is for dry, protected service. The American Wood Council’s deck construction guide DCA 6 includes a table of glulam deck beam spans but requires the glulam to be a naturally durable species or preservative treated in accordance with AWPA U1. It also says spans for glulam not treated with oil-borne preservatives must be multiplied by 0.89, a reduction its commentary ties to the wet service factor for bending. DCA 6 allows 3-1/8 inch or wider beams where its table shows 3-1/2 inches, and 5-1/8 inch or wider where it shows 5-1/4 inches.
Whatever the location, a glulam beam that carries a roof, floor or wall load must be sized by a licensed structural engineer or a qualified designer using the manufacturer’s published design values, including bearing length at each end and the connections.
Glulam Beam FAQ
Is glulam stronger than solid wood?
For the same size, yes. Defects are spread across many laminations and the best lumber is placed where stresses are highest, so glulam is assigned higher design values than a sawn timber of the same dimensions.
What does “TOP” on a glulam beam mean?
It marks an unbalanced beam, which has its strongest laminations on the tension side. The “TOP” face must go up. Installing it upside down reduces its bending capacity.
How far can a glulam beam span?
It depends on the load, the width and depth, the layup and the deflection limit. Custom glulam members span far longer than any sawn lumber, but every beam has to be sized for its actual loads by a licensed structural engineer or qualified designer.
Can I cut or notch a glulam beam?
Only where the manufacturer or engineer allows it. Notching the tension (bottom) face of a beam, especially near a support, removes the strongest laminations exactly where they are needed.
What is the difference between glulam and LVL?
Glulam is made from full-thickness lumber boards; LVL is made from thin veneers. Glulam comes in single-piece widths up to 6-3/4 inches in stock and looks good exposed, while LVL is usually built up from 1-3/4 inch plies and kept hidden.
Reference information only, not engineering advice. Disclaimer.