TruLine Truss offers a full line of LVL and I-Joist selections.
Below is some useful information we have provided to aid in your decision making process when considering these products.
LVL (Laminated Veneer Lumber): A Practical Alternative
Laminated veneer lumber (LVL) is an engineered wood product created by layering dried and graded wood veneers with waterproof adhesive into blocks of material known as billets. Cured in a heated press, LVL is typically available in various thicknesses and widths and is easily worked in the field using conventional construction tools. LVL is also known as structural composite lumber (SCL). It is mainly used in beam and header applications by providing a load beaing alternative to walls, steel, etc.
Strong, Reliable and Consistent
In LVL billets, the grain of each layer of veneer runs in the same direction, rather than cross-lamination which is typical of other engineered wood products such as plywood. The resulting parallel-laminated lumber out-performs conventional lumber when either face- or edge-loaded. LVL is a solid, highly predictable and uniform engineered wood product that is sawn to consistent sizes and is virtually free from warping and splitting.
Making the Best Use of Resources
One important benefit to LVL is that the veneering and gluing process enables large timbers to be made from relatively small trees of many species, thereby providing for efficient utilization of wood fiber resources.
The Argument for I-Joists
New products and increased competition make superior I-joist performance available at solid-lumber prices
While I-joists offer many advantages over sawn lumber, unfamiliarity and high prices have kept most builders from trying them. But the truth is that I-joist installation is not that different from solid lumber. And the really good news is that the prices of I-joists are dropping. The timber crisis of the 1990s has made prices of engineered-wood products, such as I-joists, more stable than lumber.
I-joists don't waste fiber where it's not needed
To understand how an I-joist works, imagine what happens when weight is placed in the center of the floor. As the joist deflects and bends -- essentially forming an arc -- the wood fibers along the top edge are compressed, while those along the bottom edge are stretched. Because the edges are moving in different directions, at some point the wood fibers in between are neither compressed nor pulled apart. I-joist designers take advantage of this fact by placing the strongest and stiffest fiber in the flanges where the stress is greatest. But they don't waste fiber in the center where it's not needed. This fact is why I-joists can get away with a web that's only 3/8 in. thick.
To understand further why I-joists are so efficient, it's important to understand the properties of solid lumber. Double the thickness of a joist, and it will carry twice the load; double the depth of a joist, and it will carry four times the load. Likewise with stiffness: Double the thickness of a joist, and the deflection is cut in half; double the depth of a joist, and the deflection is reduced to one-eighth. Adding depth to a joist increases strength, stiffness and potential clear span. With an I-joist, a minimal amount of wood fiber is all it takes to increase the depth.
How an I-joist works: The deflection that results from a bending load puts great strain on the top and bottom edges of lumber but has little effect on the wood in between. The flanges of an I-joist are built of strong lumber to resist these forces, while the web of an I-joist basically functions to tie the flanges together.
One I-joist can do the work of two or more solid joists
Solid-lumber joists are typically available in maximum lengths of 16 ft., and they're usually laid out 16 in. o. c. To span the average house, separate joists are installed across the front and the back, and lapped over a girder beam at midspan.
Because I-joists are available at TruLine Truss in lengths up to 48 ft., spanning the house is not a problem, so the number of joists is usually cut in half. In most cases, I-joists can be laid out on 19.2 inches O.C. or 24 inches O.C. Besides material savings, fewer joists mean less handling and less nailing.
Drilling holes in I-joists. The flanges must never be cut or notched, but fairly large holes can be cut through the webs (the largest holes are permitted at midspan). TruLine Truss staff should be consulted to determine maximum diameters for holes near supports.
Solid-sawn flanges offer I-joist quality at lower costs
The evolution of I-joists has been a combination of high and low technology. The first I-joists were made with plywood webs and solid-lumber flanges. In 1977, most manufacturers began making flange stock out of laminated veneer lumber (LVL), stronger and more stable than solid lumber. Since 1990, virtually every manufacturer has abandoned plywood in favor of oriented strand board (OSB) web material. OSB is less expensive, more widely available and--because all the strands interlock -- stronger than plywood in shear.
Recent I-joist technology has developed in lieu of solid sawn flanges: Between 15% and 20% of I-joists are now being built with solid-lumber flanges. These days, solid-lumber flanges are made from 2x3s or 2x4s that have been specially selected and finger-jointed for high strength and stiffness. The solid flanges do not have the strength of LVL, but they make up the difference with larger cross sections. Well-made solid-flange I-joists can span distances equal to the best LVL versions. And the kicker is that they typically cost 20% less than their LVL cousins.
Along with seeing material cost savings, many framers find that I-joists with wider solid-lumber flanges are easier to install: They don't wiggle while they're carried and laid up, and they don't easily tip over the way their thin-flanged LVL cousins do. Solid flanges make the joists run more true across the span, so they don't have to be straightened as much when decking is applied. Wider flanges provide more room for nailing, have virtually no splitting due from nailing as the LVL counterparts and have a larger surface area for gluing; they also slightly reduce the space between joists, making the subfloor a bit stiffer.
Additional details including span charts and design specifications can be found on the GP Broadspan web site. Click here for an automatic link to their adobe specification documents