To complete this floor series, it’s worth examining how we’re doing against I-joists. [For all graphs and images, See PDF or View in Full Issue.]
Mixed Signals: Many CMs think trusses are slowly making gains, and this is backed up by the brisk sales of floor machines. However, around here in central Virginia, most detached houses have consistently used I-joists, although some conversions came because of doubling EWP prices and shortages. This gained business may be in jeopardy though, because both Trus Joist and Boise have dropped prices to try to revive sales. And Boise is beefing up supply, taking “…meaningful steps via acquisition and organic initiatives to expand our EWP capacity,” in the words of CEO Nate Jorgensen. Yet I-joist prices remain considerably above the prices of 3 to 5 years ago.
Room for Optimism?: Another way to tell how we’re doing is to compare Boise’s and Trus Joist’s sales with single family housing starts, because that’s where they’ve been besting CMs. As shown in the graph, beginning about a decade ago, the downward trend is undeniable. Clearly some systemic factors are at work beyond the recent price volatility. And the extent of this decline is exacerbated by the fact that more floor decks are built every year due to the vertical rise of housing. For example, a four-story 2000 sq. ft. townhouse has 12% more floor area than a three-story 2000 sq. ft. house when both are built on concrete slabs. Likewise, two-story single family houses (requiring second-floor framing) are now predominant in many former ranch-style home communities.
Perhaps some solid-sawn floor joists displaced I-joists while they were on allocation, and replaced trusses when plates were being rationed. But these shortages ceased more than a year ago, and some rebound in demand should have occurred by now. Since I-joists per single family start have continued to trend downward, truss sales per single family start must have moved upward at a corresponding rate, or about 5% per year. At least some of those who recently tried trusses liked them better, especially if they previously had to cut I-joists to length or benefitted from some of these well-established pluses:
- Expedited installation of mechanicals: after working with trusses, electricians and plumbers surely don’t want to go back to cutting holes in I-joists. In addition, wiring, plumbing, and ductwork can be run diagonally, saving materials.
- Elimination of bulkheads, squash-blocks, filler blocks, and web-stiffeners.
- Ducts can pass through floor truss girders but not LVL beams.
- Duct chases can be located closer to bearings than is possible with I-joists.
Stiffer Strong-Backed Systems: In floor truss systems but not in joist systems, loads can be shared and vibrations dampened by strong-backs. To ensure that they get installed, a notch can be built into webbing, a practice developed by Hall-of-Famer Don Hershey. In these photos, two notches were formed by plating 7½” tall blocks against vertical members at the one-third points of the span. Then 2x6x24’ LSL members spanning from wall-to-wall were inserted and secured inside these notches, still leaving room for HVAC ducts.
Expensive Rim Boards: Not to be overlooked is the higher cost of closure material required with I-joists. Even at prices that are discounted from the retail prices shown in the chart, rim material will still add a considerable sum to the EWP package and should be counted in cost comparisons.
While relative prices may change, the fact remains that I-Joists are still joists, but with a less framer-friendly shape than the solid-sawn joists formerly used. Contrarily, floor trusses have a more workable rectangular shape and more convenient open webbing. While many have recognized these inherent advantages, it’s up to all of us to continue to promote them and continue the gains that trusses have made over the past decade.
Next Month:
Wall Panel Prequel
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