Engineered wood products, usually called EWP, have replaced much of the dimensional lumber in modern floor and roof framing. I-joists, laminated veneer lumber, and glulam beams carry more load over longer spans with less waste than solid lumber, and every one of them comes with published design values. The selection process follows the same logic whether you are picking a roof truss selection or a floor joist.
This article explains what each EWP family is, how designers check spans and loads, where the products sit in the load path, and how software tools turn the math into a pass or fail answer.
What Engineered Wood Products Are
Engineered wood products are made by bonding wood veneers, strands, or fibers together with adhesives under heat and pressure. The process removes the natural defects that limit solid lumber, so an I-joist or LVL beam has predictable strength, stiffness, and dimensions.
Manufacturers dry the veneers and strands to a tight moisture range before bonding, so EWP moves less after installation than solid lumber that was stored wet on the job site. That stability shows up in fewer squeaks, fewer popped fasteners, and straighter floors, which is why builders pay a premium for it on larger spans.
Product families compared
| Product | Made from | Typical use | Common depths |
|---|---|---|---|
| I-joist | Veneer flanges and OSB web | Floor and roof joists | 9-1/2 to 16 in |
| LVL | Layered veneers | Beams, headers, rim board | 1-3/4 in laminations |
| Glulam | Bonded lumber laminations | Long-span beams, columns | 6 to 24 in or more |
| PSL | Long strands | Beams, columns, headers | 3-1/2 in and up |
How EWP differs from dimensional lumber
Solid lumber carries a grade stamped by an inspector, and its strength depends on knots and grain direction. EWP is manufactured to a spec, so two pieces from the same product line behave the same way. That consistency lets engineers use tighter design values and longer spans. The general principles of construction material selection still apply, from cost per linear foot to availability and handling.
Design values and grades
Each EWP product has published bending, shear, and bearing values. Read the product’s own table rather than assuming one I-joist equals another, because flange size, web thickness, and grade all change the numbers.
How Designers Select the Right Product
Selection starts with the loads the member must carry and the space it can occupy. Dead load is the weight of the structure itself, live load is the people and furniture, and snow or wind add their own requirements. Span, spacing, and deflection limits turn those loads into a pass or fail check.
The selection workflow
- Record the span, spacing, and support conditions from the framing plan.
- Add up the dead and live loads for the area, including snow load where it applies.
- Pick a candidate product and read its span table for the given spacing.
- Check deflection limits, usually L/360 for floors and L/240 for roofs.
- Verify bearing length and hanger capacity before locking the choice.
Span tables are organized by load, spacing, and member depth, and each cell lists the maximum span for that combination. The tables assume simple supports, uniform loading, and specific bearing lengths, so a floor with point loads or cantilevers needs a different calculation than the table shows.
Software tools that do the math
Designers and specifiers now use software that takes the same inputs and returns a clear result in seconds. These tools remove the arithmetic errors that happen when a span table is read across the wrong row. The same idea of simplifying repetitive layout work has a long history on site, where jigs and bumpers simplify stair construction by replacing hand measurement with fixed spacers.
What the math covers
A full check covers bending stress, shear at the supports, deflection under live load, and bearing at each end. Failing any one of those rejects the member, and the next candidate starts the process again.
Matching the Product to the Load Path
Every member carries its load to something below it. Roof joists hand loads to beams, beams to columns, columns to the foundation, and the foundation to the soil. The EWP chosen at each level has to fit the loads handed down to it.
Floor and roof systems
I-joists work well for floors because the open web leaves room for ducts and wiring. Floor and roof systems use different load assumptions, so a product sized for a floor does not automatically work as a roof member. Check the roof table separately, because snow load and live load rarely match.
Beams and headers
LVL and glulam carry the concentrated loads where joists bear. Bearing length matters: too short a seat crushes the wood fibers, and too long a span under a point load fails the shear check. When heavy loads reach the ground, the foundation type follows the soil, and foundation selection by soil type decides whether spread footings or piles carry the building.
Lateral loads matter too. Wind pushes against the roof, and the diaphragm action of the floor and roof sheathing carries that force down to the walls. EWP members are designed for vertical loads, but their connection details, hangers, and rim boards have to transfer the lateral forces without splitting.
Support conditions change capacity
A member supported at both ends carries less than a continuous member over three or more supports. Note the support condition when you read the table, and never mix values from different support assumptions.
Common Selection Mistakes
Most EWP problems are not material defects; they are selection errors that put the wrong member in the wrong place. A few mistakes repeat across jobs.
Mistakes and consequences
| Mistake | Result |
|---|---|
| Overspanning a joist | Bounce and sag under live load |
| Ignoring point loads | Cracks at bearing or hanger |
| Wrong support condition | Overstated capacity, local failure |
| Skipping deflection checks | Floors that feel springy |
| Using treated lumber specs | Corrosion of connectors and fasteners |
Bearing and hanger details fail before the member does. A joist hanger sized for the flange width, with nails driven through every hole, transfers the load the way the table assumes. Short nails, missing nails, and oversized holes cut the connection capacity in half.
Checking the table twice
Read the span table once for the span and once for the spacing, then confirm the load column. When the design relies on deep foundations under heavy loads, the same double-checking applies to pile foundation selection based on soil condition, where a wrong assumption is expensive to fix.
When in doubt, go up a size
If the check lands within a few percent of the limit, a larger member buys stiffness and margin for load changes later, usually for a small cost difference on a single beam.
Using Software Tools for Selection
Selection software does not replace engineering judgment; it removes arithmetic and speeds up the compare loop. Enter the geometry once, run the checks, and read the result.
What to enter
- Member type and product line.
- Span, spacing, and support conditions.
- Dead, live, and snow loads.
- Deflection limit and bearing length.
- Hanger or connection type at the ends.
Reading the results
The output shows whether the member passes each check and, when it fails, which limit was exceeded. A failing result for deflection usually means a deeper member, while a shear failure means more bearing or a stronger product. The same pass-fail discipline shows up in pad foundation design principles, where the footing size is checked against soil bearing capacity before any concrete is ordered.
Run the same project through two or three product lines before choosing. Manufacturers publish different values for the same nominal depth, and the cheapest member is not always the one that passes every check. A few minutes of comparison avoids a change order later.
Verifying software output on site
Compare the delivered member against the drawing: depth, grade stamp, and product name. Software is only as good as the inputs, and a member swapped at the lumberyard without a recheck voids the design.
From Selection to Installation
The best selection fails if the member is damaged before it is installed. EWP is strong along its length and vulnerable across it, so handling and storage decide whether the product arrives intact.
Delivery and storage
Store I-joists and LVL flat, off the ground, under cover. Water that wicks into the ends of an I-joist web can delaminate the veneers, and a twisted stack can set a permanent bow in the members.
Field checks before installation
Check every member for cracked flanges, delaminated webs, and end splits before lifting it into place. Confirm hangers and bearing seats match the drawings, and set the members before the structure below changes. The framing package only works when every level agrees, from the footing to the ridge, and reviewing the foundation selection criteria for the building before the first joist is set catches mismatches early.
Ordering is where selection errors surface. Count the members by depth and grade, check the delivery against the takeoff, and set aside damaged pieces for return before the crew starts cutting. A mismatch found at the lumberyard costs a phone call; one found on the deck costs a day.