Open Web Joists Vs. Wood i-beams

Open Web Joists Vs. Wood i-beams

For those of you working on your home's specifications or in the process of building, I’m curious about your choice: open web trusses or solid wooden i-beams? I'm trying to understand the differences. Two of the builders I'm consulting with use open web trusses, but the third prefers solid i-beams, claiming they are stronger. I initially thought that using i-beams when open web trusses could suffice might be over-engineering, but I'm not well-versed in this area. Can anyone offer detailed insights? If both options are adequate, with one being cheaper and easier (open web), why opt for the more expensive one?

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The Advancement of Engineered Wood I-Joists

Please note: This older article by our former faculty member remains available on our site for archival purposes. Some information contained in it may be outdated.

Previously, engineered I-joists were expensive options for framing in upscale custom homes. However, expansions in product lines and competitive market forces now offer builders high performance at more affordable costs.

Trus Joist Corporation (TJ) pioneered the wood I-joist industry. “In 1969, as Apollo 11 landed on the moon, Trus Joist Corporation introduced the first wood I-beam.” TJ led in this new market, facing stiff competition which spurred rapid technological advancements beneficial to builders. Originally, there was one product and one price from TJ, but now builders have a variety of brands, prices, and service levels to choose from.

Cost and performance were key in developing wood I-joists. They gained popularity in the 1970s as homeowners favored open floor plans requiring long clear spans. While long lumber joists over 20 feet existed, they were expensive and lacked adequate load-carrying ability. Enter I-joists with deep plywood webs and robust lumber flanges. These made less restrictive load-bearing strategies possible. Although early I-joists were costly, they were straight, lightweight, and effective. The timber crisis in the 1990s stabilized engineered wood prices compared to lumber, an attractive feature for builders when quoting bids.

Product Innovation
I-Joists initially featured plywood webs and solid lumber flanges until 1977, when TJ introduced Laminated Veneer Lumber (LVL) for its flanges. This innovation resulted in continuous LVL production, enabling longer I-joist lengths. LVL flanges, made from carefully selected veneers, are known for high strength and stiffness.

Another pivotal moment was the transition from plywood to oriented strand board (OSB) web material in 1990. OSB is cheaper, more available, and stronger in shear. Today, nearly all I-joist manufacturers use OSB webs in their residential and commercial lines.

Market Dynamics and Leaders
TJ's evolution influenced technological advancements that shaped the I-joist industry. TJ International partnered with MacMillan Bloedel in 1991, which later merged into Weyerhaeuser Company, the largest forest products company in the U.S.

Trus Joist dominates the market with an estimated 55% share of the $750 million U.S. I-joist market in 1999. However, competition from Boise Cascade, Louisiana-Pacific, Willamette Industries, and Georgia Pacific, which share the remaining market, drives the industry forward. Smaller manufacturers offer competitive products at lower prices, benefiting builders.

Performance and Benefits
Wood I-joists outperform sawn lumber in many aspects. They offer design flexibility, increased span potential, improved strength and stiffness, consistent sizes and performance, dimensional stability, lighter weight, ease of drilling for utilities, and reduced waste. High initial prices and unfamiliarity once limited their use, but increasing knowledge and training have led to greater acceptance.

Lumber joists are usually available up to 16 feet and installed at 16-inch centers, often requiring a supporting beam at mid-span. In contrast, I-joists available in lengths up to 60 feet can span larger areas without mid-span support, reducing the number of required joists. The cost-effectiveness of installing a center beam enhances their appeal.

Increasing on-center spacing to 19.2 or 24 inches improves performance compared to 16-inch spacing in traditional lumber framing. I-joists simplify deck nailing and reduce labor. Additionally, they can be used in cathedral roofs for energy-efficient designs with ample insulation and ventilation space.

Choosing the Right I-Joist
Selecting the right I-joist brand involves evaluating performance, service, and price. While performance differences among major brands are minimal, service quality varies significantly. Builders should inquire about engineering service providers, lead times for sizing, delivery times, and technical support for changes and defects.

Standard I-joist depths range from 9-1/2 to 16 inches for residential applications. Commercial lines offer deeper options up to 32 inches. LVL flanges are typically 1-1/2 inches square, while solid lumber flanges use finger jointed 2x3s or 2x4s. Although LVL is stronger, solid lumber flanges are more cost-effective for residential applications.

Builders' Experience
Builders who transition to I-joists often remain loyal. Art Pakatar of Belmonte Builders in Albany, NY, reports saving $1,400 per home by using sawn-flange I-joists, appreciating their cost-effectiveness and performance.

Builders also find fewer issues with splitting when nailing I-joists to sills and walls. Solid lumber flanges are stable and easier to handle during installation, reducing wiggle and improving alignment. The broader flanges facilitate better bonding with subflooring and greater construction accuracy.

Promotional claims of big savings in plumbing, electrical, and mechanical installations are not always realized. However, builders appreciate the consistency and stability of I-joists, resulting in flat floors and ceilings, and fewer issues like shrinkage and floor squeaks.

Distribution varies regionally, so builders should plan ahead for special orders. Strong networks from major companies like TJ provide reliable availability.

Standardization Efforts
APA The Engineered Wood Association aims to standardize I-joist specifications and span recommendations. This initiative, known as APA Performance Rated I-Joist (PRI), simplifies product selection for builders and suppliers. Despite resistance from major manufacturers, APA believes standardization benefits the industry by reducing confusion and improving consistency.

Some concerns about standardization include potential drive towards lowest common denominators and reduced innovation incentives. However, APA addresses these issues and advocates for continued technical support and design services alongside standardization.