LVL & I-Joist Sizes: Engineered Lumber Explained

What Counts as "Engineered Lumber"?

Engineered lumber is manufactured, not sawn from a single log. Thin wood veneers or strands are bonded together under heat and pressure into a product with far more dimensional consistency than a solid-sawn 2x10 cut from one tree. The three you'll run into most on a residential job:

LVL (Laminated Veneer Lumber): Thin wood veneers glued in layers, all grain running the same direction. Used for beams and headers.
I-Joists: An LVL or solid-sawn flange on top and bottom, connected by an OSB web — literally shaped like a steel "I" beam. Used for floor and roof framing.
Glulam (Glue-Laminated Timber): Larger dimensional lumber boards glued face-to-face into a big structural beam, often left exposed as a design feature.

Why There's No Nominal-vs-Actual Gap Here

Dimensional lumber (a 2x4, a 2x10) is named for its rough-sawn size before drying and planing shrink it — that's the entire subject of why a 2x4 isn't 2 inches by 4 inches. Engineered lumber skips that process. It's built up to a target dimension in a factory press, so the number on the stamp is the number you get. An "11⅞" LVL beam is manufactured to measure 11⅞" — not shrunk down from something larger.

That's also why engineered lumber depths are chosen to match dimensional lumber's actual (not nominal) depths — an 11¼" LVL lines up with the actual depth of a 2x12, so it can be swapped into a framing plan without changing every other measurement around it.

Common LVL Depths

LVL is almost always 1¾" thick (single-ply), with common depths of:

Depth	Matches actual depth of
5½"	2x6
7¼"	2x8
9¼"	2x10
9½"	—
11¼"	2x12
11⅞"	—
14"	—
16"	—
18"	—

Multiple 1¾" plies get bolted or nailed face-to-face for a wider beam (two plies = 3½" thick, matching a 4x post; three plies = 5¼", and so on).

Common I-Joist Depths

I-joists are sold by depth only, most commonly 9½", 11⅞", 14", 16", 18", and 20" — with flange widths and web thickness varying by manufacturer and load rating.

Manufacturer variance matters here: Unlike dimensional softwood lumber, which follows one nationwide standard, engineered lumber depths, flange sizes, and load ratings are brand-specific (TimberStrand, Microllam, Versa-Lam, BCI, TJI, and others). Always pull the specific manufacturer's span and load tables rather than assuming one brand's 11⅞" I-joist is rated identically to another's.

When to Use Engineered Lumber Over Dimensional

Long spans: Engineered lumber typically spans farther than solid-sawn lumber of the same depth before it needs a mid-span support.
Consistency: No knots, no crown to sight and orient, minimal twisting or warping over time — useful where a straight, flat floor matters.
Big headers and beams: Multi-ply LVL is a common replacement for oversized dimensional headers over wide openings (garage doors, large window walls).

Dimensional lumber still wins on cost and availability for anything a standard 2x will span — engineered lumber earns its higher price on longer spans and bigger openings, not everywhere.

Need the actual size of a standard 2-by?

See actual dimensions for every common dimensional lumber size, from 1x2 up to 6x6.