By Scott Milano
An I-joist is an I-joist, right? Well, yes and no. They're not all the same. Unlike commodity-based solid sawn lumber, I-joists differ from manufacturer to manufacturer.
Some manufacturers use oriented strand board (OSB) webs instead of plywood webs. Some make their I-joists with solid sawn flanges while others use laminated veneer lumber (LVL). The difference in materials alters the performance and installation.
For example, when comparing an OSB web I-joist to a plywood web I-joist, the OSB web I-joist offers a higher shear performance, says Mike Hunsaker, general sales manager for Willamette's engineered wood products. A higher shear performance means a more stable surface to walk on once the floor has been laid.
Aside from the composition of the web, the flange material also alters the way the finished floor feels. I-joists with LVL flanges differ from those made with sawn lumber flanges. According to Mike O'Day, Georgia-Pacific's area manager for engineered lumber, "The floor tends to feel stiffer with a wood flange [while] the LVL gives it a more cushiony feel." Once the product is installed, you can notice this difference, O'Day adds.
Performance is important, but builders are concerned about installation too. Installing I-joists requires different blocking and cutting techniques than those used with sawn lumber, so there is a learning curve for workers who are inexperienced with the product, which is why some builders haven't made the switch from sawn lumber.
Many builders in the southern states, like Florida and Texas, prefer open-webbed I-joists because electricity, plumbing, and HVAC can be easily routed through the joist without cutting holes in the joist. There are a number of smaller companies that produce open-web I-joists, and sources say a larger firm plans to introduce its new open-web product in late 2001.
Even though product performance and installation are key issues for I-joist manufacturers and builders, consistency in market growth is equally important for development.
Throughout the last 15 years, the I-joists market has seen tremendous growth, says Jack Merry, communications director for APA-The Engineered Wood Association (APA). However, since 2000, I-joist growth has slowed due to lower lumber prices. Merry estimates that I-joists have about 40 percent of the wood flooring market. And I-joist manufacturers are interested in increasing their market share and eventually overtaking sawn lumber's majority hold.
Unlike solid sawn lumber, I-joists are not made to universal sizing and rating standards. This makes it difficult for builders to compare I-joists to regular sawn lumber. O'Day says the first question he hears builders ask their dealers is, "What do you have that replaces a 2x10?" This incommensurability issue, in addition to lower lumber prices, is a major reason why more builders haven't switched.
In order to combat the conversion problem, the APA is promoting its PRI-400 program. The program, which was introduced in 1997, is a method of standardizing I-joists. Currently, about 30 percent of I-joist production is manufactured in accordance with the PRI-400 standard. The long-term goal of PRI-400, according to Merry, is to make I-joists sufficiently standardized so that builders and contractors can easily find out which sizes, spans, and spacing they'll need for which applications.
On the other hand, Trus Joist--the largest manufacturer of I-joists with 50 percent to 60 percent of the market share--is not a member of the APA. Gary Schweizer, Trus Joist's engineering manager for residential operations, believes the PRI-400 is more of a commodity initiative. He thinks it drives production to the lowest common denominator--cost. This, in his opinion, may eventually compromise the quality of the finished product.
With a universal standard still to come, what other I-joist innovations are on the horizon? Manufacturers are poised to streamline their manufacturing processes and still maintain product performance.
Companies like Willamette, for example, may take lower-grade species of wood and engineer them to meet APA strength requirements, helping further reduce the cost without sacrificing quality and strength.
"I expect to see innovations in flanges," says Hunsaker. Efficient engineering and production of stronger and wider flanges could allow builders to enlarge spacing, which would reduce the amount of product used in the application.
Balance beams: The WI and GPI series Wood I Beam joists feature the
Georgia-Pacific's FiberStrong OSB web. Both series come with wide flanges that
allow for longer spans and greater load carrying capacity, the company claims.
The WI series features solid sawn lumber flanges available in 3-inch widths.
The GPI series is equipped with 2-inch LVL flanges. Georgia Pacific. 800-284-5347.
Strand tall: The flange material for TJI joists is TimberStrand laminated strand lumber (LSL). Covering the top and bottom of the Performance Plus web, LSL flanges are made from aspen and poplar trees. Trus Joist converts these trees into high-strength engineered lumber that is available in a variety of depths and lengths for residential roof and floor applications. Trus Joist. 800-338-0515. www.trusjoist.com.
Hoist the joist: The BCI Advantage series I-joist is equipped with a flange depth of 1 5/16 inches instead of the traditional 1 1/2 inches. This, according to the maker, offers a lightweight joist that is easier to handle and faster to install compared to conventional lumber. The series features an OSB web. Boise Cascade. 800-222-4845. www.bc.com.
Joist a minute: StrucJoist I-joists are available with either LVL flanges or machine stress­rated lumber. The joists' webs are manufactured from OSB. Designed for residential applications, the joists are available in common industry-standard sizes. Willamette. 888-650-6332. www.wii.com.
Endearing engineering: Used for a variety of residential, commercial, and remodeling applications, the LPI 200, 225, 300 series joists have top and bottom flanges made from ultrasonically graded veneers that are bonded with exterior adhesives. The OSB webs allow plumbing and wiring to pass through without extra framing. The 300 series is available in 2 5/16-inch wide flanges. LP Corp. 800-299-0028. www.lpcorp.com.