Since the 1960s, fabricators have used machine stress rated (MSR) lumber of all species to improve the performance and reliability of their engineered components and structures. Nowadays, you don’t have to look far to find a successful component manufacturer who relies heavily on MSR grades to produce high quality roof trusses, floor trusses, and wall panels. While the reasons to use MSR are numerous, they all boil down to one word: quality.
Rigidply Rafters in Richland, Pennsylvania, is a family-owned operation that has been building roof and floor trusses since 1963. President Vernon Shirk says the company has been using MSR in their products for more than 35 years. “It’s really helped our business,” he says. “We know it’s something we can count on. We are providing an engineered product, so MSR is crucial to that.”
Dave Kipp, Purchasing Manager for Structural Component Systems (SCS) in Fremont, Nebraska, agrees. “We’ve been using MSR pretty much since day one when SCS was founded in 1987,” he says. “It’s a crucial element for roof and floor trusses, especially with today’s challenging designs for residential and commercial construction.”
“By using MSR, we reduce the overall fiber required for the design of our products,” says Kipp. “For example, a top chord on a roof truss might require 2x6 if only #2 is available but that can often be replaced with a 2x4 in MSR. Likewise, floor trusses may require more webs if the chords are #2 but using MSR can allow us to reduce the number of webs and/or the size of the connector plates used.”
Clear span flexibility is another benefit of MSR’s consistent strength values enjoyed by companies like Rigidply. “One of our specialties is large span trusses for ag and commercial projects (60-100' clear span),” explains Shirk. “MSR helps in that part of the business, too. Designers can rely on MSR properties, use full-design strength, and avoid overbuilding.”
Why is MSR key to a quality truss? In contrast to visual grades, machine rated lumber production is centered on measuring the physical properties of each piece of lumber on the line. MSR manufacturers are required to test samples during each shift, and independent third parties audit the entire quality assurance process to confirm conformance with published design values. This testing process verifies that production consistently meets design value requirements even as timber growing practices and environmental conditions change.
The result? Component manufacturers have confidence in MSR’s higher strength values, which in turn provides greater design flexibility. This allows truss designers to optimize the lumber in each truss, resulting in a more efficient use of materials and lower installed costs.
Steve Szymanski of Drexel Building Systems in Little Chute, Wisconsin, has been involved with truss design for 33+ years and says he wishes more truss designers understood the value of optimization in truss design. “The analogy I like to use is cooking,” he says. “There can be similar recipes for a certain type of dish but it’s the cook who chooses high quality ingredients and uses them in just the right amounts that usually produces the best end product. The same is true when using MSR lumber to optimize truss designs. Because there are more grades to choose from, you can make a more cost-effective truss.”
Szymanski says he often uses a basic floor truss system to illustrate the overall installed cost savings with customers: “I explain that, because we can be confident in the higher design values and deflection properties of MSR, we can often use fewer trusses in the floor system as a whole – placing components 19.2 inches on center instead of 16. Less lineal footage of product to install means a lower installed cost, while delivering a high performance floor that doesn’t sacrifice loading capacity.”
Consider this example from Szymanski that maximizes the benefits of using MSR lumber in his optimized designs to create a high performance, cost effective product. Shown are two drawings of the same 22’ floor truss: the first truss is designed with 2x4 SPF No. 2 and the second truss is designed with 2x4 SP 2850F 2.3 MSR lumber. [For images, see PDF or View in Full Issue.]
While the drawings are almost identical, the performance that results from Szymanski’s optimization of the design is particularly noteworthy. The floor truss designed with the MSR grade can be spaced 19.2” on center, instead of the tradition 16” on center, saving the builder one truss for every eight feet of floor system. What’s more, the MSR-built system will perform better as the design values of the MSR deliver approximately 23% lower deflection. While these optimized trusses might cost a bit to build due to slightly larger plates and higher quality lumber, overall installed costs will go down as fewer trusses and less framing labor is needed.
Rigidply’s Engineering Manager agrees that using MSR is key to truss design optimization. “Our designers are always looking to reduce the amount of web lateral bracing required by increasing the lumber grade to our MSR options,” explains Tim Riegel, PE. “Reduced lateral bracing requirements reduces the installed cost and overall amount of lumber needed within a roof system. I think it’s one of the biggest benefits of using MSR lumber.”
Last but not least, wood continues to be one of the most renewable resources for use in a variety of applications. In addition to consistent strength, high quality, and increased flexibility for optimized design, every single piece of MSR lumber can be used to the maximum, which allows component manufacturers to turn inventory faster and reduce waste costs. At the end of the day, the combined benefits of using MSR lumber demonstrate a clear commitment to quality and make the engineered components even more marketable.
The bottom line for those considering a move to using more MSR lumber in trusses? Shirk says, “you know what you’re working with and that broadens your capabilities.”
For more information on common grades of MSR lumber and design values by species, visit the MSRLPC website.