When a wall opening gets wider than about 6 feet, solid lumber stops being the practical choice for the beam above it. A built-up header of 2x10s works, but it eats into the opening height and still sags or twists after a few seasons of humidity swings. Engineered beams solve that problem with wood that has been dried, graded, and glued into a product with predictable strength. Microllam is the best-known brand name for laminated veneer lumber, or LVL, and the product has become the default header and beam material in new residential framing.
What LVL Actually Is
Laminated veneer lumber is a manufactured wood product built from thin sheets of veneer, usually Douglas fir, Southern pine, or yellow poplar. Rotary peelers strip each log into a continuous sheet about 1/10 inch thick, the sheets are dried and graded, and then they are glued together with all grain running the same direction and pressed into a solid billet. Because defects like knots and slope of grain are either removed or spread across many layers, the finished product has far less variability than a solid board cut from the same log.
How the Manufacturing Process Works
The key steps in the process are consistent across every LVL plant:
- Logs are debarked and softened in hot water before peeling.
- A rotary lathe peels each log into a continuous veneer ribbon.
- Veneer is clipped into sheets, dried to about 6 percent moisture, and graded.
- Sheets are laid up with grain parallel, adhesive applied, and the pack pressed in a continuous hot press.
- The cured billet is sawn into beams of the ordered width, depth, and length.
The adhesive is a structural exterior-grade resin, the same family used in marine plywood, so the glue line holds up to the moisture a beam sees inside a wall cavity. Pressing at high heat and pressure compacts the veneers, which is why LVL runs denser and stiffer than the solid lumber it replaces. A typical billet leaves the press at a density that tests 20 to 30 percent stronger in bending than an equivalent piece of solid framing lumber.
Veneer Grading and Layup
Each veneer sheet is graded for strength and appearance before layup. Face veneers take the highest grade because they carry the outer fibers, while core plies can contain small knots and patches. Grain direction in every ply runs parallel to the beam length, which is what separates LVL from plywood, where the grain alternates to give panel stiffness in two directions.
How LVL Compares With Solid Lumber and Glulam
Engineered beams compete with two other products on the framing floor: solid sawn lumber and glulam. LVL wins on consistency and length, glulam wins on very long clear spans, and solid lumber wins on price for short spans. Fine Homebuilding documented a house where 13 Microllam beams frame a roof skeleton, replacing a pile of built-up 2x material with a handful of long, straight members that carried the roof without posts in the middle of the room.
Strength and Stiffness Compared
The engineering values tell the story. A 1-3/4 by 11-7/8 inch LVL beam typically carries more load over a longer span than a 4×12 solid beam of the same depth, and it weighs less because the dry veneers and dense pressing remove most of the water weight. Design values published by the manufacturer are certified, so an engineer can spec the beam from a table instead of applying a safety factor to variable lumber.
| Product | Typical length | Strength consistency | Dimensional stability | Best use |
|---|---|---|---|---|
| Solid 2x lumber | Up to 20 ft | Variable by grade | Shrinks, twists, cups | Short headers, studs |
| Built-up 2x header | Up to 16 ft | Each ply moves alone | Layers separate over time | Mid-size openings |
| LVL beam | Up to 60 ft | Certified design values | Very stable | Headers, long beams, rim board |
| Glulam | Up to 100 ft | Certified design values | Stable, can be curved | Very long and curved spans |
Why Headers Use LVL
Headers sit directly above doors and windows, so any sag transfers straight to the frame and to the drywall corners. An LVL header is straight when it arrives, stays straight as interior humidity changes, and carries the concentrated loads from floor joists and roof rafters that land above the opening. Builders use two 1-3/4 inch plies for most residential headers, nailed together to make a 3-1/2 inch beam that fits flush in a 2×4 wall.
Sizes, Grades, and Load Ratings
LVL is sold in a narrower range of sizes than solid lumber, and that is deliberate. Standard thicknesses are 1-3/4 inches for one ply and 3-1/2 inches for two plies, with 1-1/2 inch and 2-1/2 inch products for specific applications. Depths follow the same 1-1/2 inch increments as floor joists: 7-1/4, 9-1/4, 9-1/2, 11-7/8, 14, 16, and 18 inches, so the beam ends flush with the joists it supports.
Choosing a Size From the Span Tables
Manufacturers publish span tables that match a beam size to a span and a loading condition. The tables assume a specific dead load, live load, and deflection limit, usually L/360 for floor beams, so changing the use of the room can change the required size. A beam sized for a bedroom floor does not automatically work under a living room with a full bookcase load.
| Two-ply beam size | Max span at 10 ft tributary | Max span at 14 ft tributary |
|---|---|---|
| 1-3/4 x 9-1/4 in | 11 ft 6 in | 8 ft 4 in |
| 1-3/4 x 11-7/8 in | 15 ft 0 in | 11 ft 2 in |
| 1-3/4 x 14 in | 18 ft 2 in | 13 ft 6 in |
These are representative values for a 40 psf live load, not a substitute for the manufacturer’s tables or a stamped design. Building codes require the installed beam to match the engineered drawings, and the local building department checks the grade stamp against the approved plans before the framing inspection is signed off.
Reading the Grade Stamp
Every piece of LVL carries a stamp that identifies the manufacturer, the product name, the design values, and the standard it was tested to. The stamp also shows the code evaluation report number, which is the document the inspector uses to confirm the product is approved for the application. If the stamp is missing or illegible, the beam does not get installed until the supplier replaces it.
Where LVL Beams Show Up in a House
Walk through a modern house under construction and LVL appears in the same places every time: over wide windows and patio doors, down the center of the house where the floor joists meet, and around the perimeter as rim board.
Headers, Beams, and Rim Board
- Headers over windows and doors wider than 3 feet
- Girder beams under the floor system, supported on posts or bearing walls
- Rim board around the floor perimeter, tying the joists together
- Garage door headers, where the opening spans 16 to 18 feet
- Scaffold planks and temporary shoring on commercial jobs
Roof and Floor Framing
Roof framing uses the same product at a bigger scale. Ridge beams, valley beams, and the headers that carry second-story loads are all sized from the same LVL tables, and the beams often run the full length of the house without intermediate posts. On a roof, the beam carries both the dead weight of the framing and the live snow load, so the tables separate those two conditions.
Installing an LVL header follows a set sequence that keeps the load path intact:
- Measure the rough opening and order the beam to the exact depth with extra length for bearing.
- Build the king studs and jack studs at each end, sized for the required bearing length.
- Set the beam plumb and level, resting on the full bearing surface at both ends.
- Nail the plies together with the manufacturer’s nailing pattern, usually pairs of 10d nails every 16 inches staggered.
- Add the approved hangers or framing anchors before any load goes on the beam.
- Have the framing inspected before floor or roof sheathing covers it.
The sequence matters because an LVL beam cannot be retrofitted once the load is on it. Getting the bearing and the hangers right at rough-in is the difference between a header that carries the house for decades and one that settles and cracks the finishes above it.
Field Rules for Cutting, Bearing, and Fastening
LVL arrives as a finished structural member, and field modifications are limited. The manufacturer’s instructions allow cutting to length with a carbide blade, but they forbid notching and drilling in the middle third of the span, where bending stress is highest.
Cutting, Notching, and Hole Rules
- Cut to length only; never notch the top or bottom of a beam
- Drill holes only in the end thirds, and only per the manufacturer’s hole chart
- Seal field-cut ends with the supplied end sealer or exterior paint to block moisture
- Predrill fasteners within 1-1/2 inches of edges to prevent splitting
- Never rip an LVL down in width; order the width you need
Bearing Lengths and Connections
Bearing is where most field mistakes happen. LVL needs a minimum of 1-1/2 inches of bearing at end supports and 3-1/2 inches at intermediate supports, and the bearing surface must be flat, level, and continuous. Joist hangers and face-mount hangers must match the beam depth exactly, because the load path runs through the hanger into the supporting wall.
Engineered lumber costs more per linear foot than solid 2x stock, but the trade pays for itself in labor and callbacks. A straight LVL header goes in once, carries the rated load without creeping, and never needs shimming after the first season of humidity. That predictability is the reason builders treat LVL as the default for anything that spans more than a door opening.