Overview
Engineered wood products (EWP) are manufactured structural members built from smaller pieces of wood glued under heat and pressure. The family covers laminated veneer lumber (LVL), glued-laminated timber (glulam), I-joists, parallel strand lumber (PSL), laminated strand lumber (LSL), and rim board. They exist because sawn lumber hits limits fast. A solid 2x12 crowns, twists, and checks as it dries, and it tops out on span well before a modern floor plan wants it to. EWP carries longer clear spans, holds its shape, and shows up straight off the truck instead of needing you to cull the bad sticks. It also makes better use of the forest, since you can build a strong beam out of fast-growing small-diameter trees that would never yield a clean wide timber. The tradeoff is real. EWP costs more per piece, it's fussier about water than a chunk of doug fir, and it comes with install rules that are not optional. You follow the manufacturer's span tables, hole charts, and hanger specs, or the warranty and the engineering both walk out the door. Treat it as a system, not a fancier 2x10. For plain dimensional lumber sizing, see our framing lumber sizes guide; this one is about the engineered stuff.
LVL and Glulam Beams
LVL (laminated veneer lumber) is thin wood veneers peeled off a log, dried, and glued together with the grain all running the same direction, then sawn into beam stock. Because every layer pulls the same way, you get a strong, dead-straight member that's predictable in bending. LVL comes in standard depths and a fixed ply thickness, usually 1-3/4 inch, so you build up a beam or header by nailing or bolting plies side by side until you hit the width the engineer called for. It's the default for flush beams, garage door headers, and ridge beams. Glulam (glued-laminated timber) is different stock: full dimensional lumber laminations stacked flat and glued into big sections. Glulam goes bigger than LVL plies and can be cambered, meaning it's built with a slight upward arch so it flattens under load instead of sagging. It also takes a finish well, so it's the pick when the beam is exposed in a vaulted ceiling or a timber-look great room. Rule of thumb: reach for LVL when the beam is buried in the framing and you want strength and straightness cheap; reach for glulam when you need a larger section, a camber, or a member somebody is going to see.
I-Joists for Floors and Roofs
An I-joist is shaped like a capital I. The vertical center, the web, is usually OSB or plywood. The top and bottom, the flanges, are LVL or finger-jointed sawn lumber, glued into routed grooves. That shape puts material where bending stress actually lives and strips it out of the middle where it doesn't, so the joist is light, straight, and spans far. A floor framed in I-joists feels flat and quiet because every joist is identical and nothing crowns. Now the rules, because this is where crews get in trouble. You never cut, notch, or drill the flanges. The flanges carry the load, and nicking one is how a floor fails. Holes go in the web only, sized and located per the manufacturer's hole chart, which ties hole size and spacing to the joist's depth and where it sits in the span. Many I-joists ship with prescored knockouts for wiring and small plumbing. At bearing points and under point loads like a post above, you add web stiffeners (also called bearing stiffeners), and you set squash blocks where a load passes straight through the floor to the wall below. Skip those blocks and the flange crushes.
PSL, LSL, and Rim Board
PSL (parallel strand lumber) is long thin strands of veneer glued under pressure with the grain running lengthwise. It's the strongest of the strand products, so it earns its keep as heavily loaded beams and as columns, the posts that carry a multi-story point load down to the foundation. You'll see it spec'd where an LVL would have to get impractically wide. LSL (laminated strand lumber) uses shorter strands and runs a bit less strong, but it's stiff, dimensionally tight, and cheaper. That makes it the workhorse for rim board, window and door headers, and tall wall studs, the 10-, 12-, and 16-foot studs in great rooms and entries where a sawn 2x6 would bow. Rim board is the flat member that closes off the floor system at the ends of the joists, running around the perimeter. It does real structural work: it holds the joist ends plumb and transfers the load from the wall above down through the floor to the wall below. Plain OSB or a random board won't do, because rim board is rated for that vertical load path. Match the rim board depth to your joist depth and use the product the joist manufacturer pairs with their system.
Install Rules That Matter
EWP lives or dies on the manufacturer's specs, and those specs are printed in the installation guide for a reason. Start with span and load: use the published tables for the exact product and series, because an I-joist from one maker is not interchangeable with another's. On I-joists, never notch or drill a flange, ever. Web holes go in per the hole chart only, sized to the clear distance between the flanges minus about a quarter inch, kept back from bearings, and limited in number per span. Hangers have to be the ones rated for the product, installed with every nail hole filled, and your bearing length at each end has to meet the minimum (commonly 1-3/4 inch for I-joists). Add web stiffeners at hangers and point loads and squash blocks where load runs through the floor. Keep it dry. Engineered wood will drink standing water, swell, and start to delaminate if it sits wet through a framing season, so cover stacks and shed water off the deck. And brace your I-joists temporarily before the sheathing goes on. Bare I-joists are tall and skinny and will roll over sideways under a worker's weight. Strut lines and rim attachment hold them upright until the subfloor locks them in. The APA - The Engineered Wood Association (apawood.org) publishes the construction guides that back all of this.
Common Mistakes
I see the same handful of failures over and over. The big one is cutting or notching I-joist flanges to run a duct or a drain. That ends the joist's structural life, full stop, and no glue or scab fixes it. Right behind it: drilling random holes wherever the plumber felt like it, ignoring the hole chart on size, spacing, and distance from bearing. Next is leaving off web stiffeners and squash blocks under point loads and at bearings, so the flange crushes and the floor settles. Leaving EWP exposed to weather is another quiet killer; a beam that sat in standing water all winter can swell and delaminate before it's ever loaded, and you won't always see it from outside. Swapping a spec'd LVL or glulam for sawn lumber because the yard was out of stock is a substitution only an engineer can make, since the whole design was sized around that member. And the dangerous one: setting I-joists with no temporary bracing and then walking the floor. They roll, they go over like dominoes, and people get hurt. None of these are hard to avoid. They just require reading the guide before the saw comes out.
FAQ
Can I drill a hole through an I-joist for plumbing or wiring? Through the web, yes, following the manufacturer's hole chart for size, spacing, and distance from the bearing. Many I-joists have prescored knockouts for small lines. Through the flanges, never. The flanges carry the load and cutting one ruins the joist.
What's the difference between LVL and glulam? LVL is thin veneers glued grain-parallel into straight beam stock you build up in plies, best for buried headers and flush beams. Glulam is dimensional lumber laminations glued into larger sections that can be cambered and finished, best for big spans and exposed beams.
Why does engineered wood need to stay dry? It's held together with glue and built from many layers. Sitting wet for an extended period lets it absorb water, swell, and start to delaminate, which weakens the member. Keep it covered and shed water off the deck during framing.
Can I substitute a regular 2x for a spec'd LVL if I'm short? No. The structure was engineered around that specific member's strength and stiffness. Any substitution is a call for the engineer of record, not a yard decision.