Tfuss specifrers asking for

1f-\NE OF the earliest forms of \-Iengineered wood is experiencing a "renaissance" in demand. It's a growth market for retail dealers as more builders and truss producers specify machine stress rated (MSR ) lumber for chords of roof and floor trusses, plus other types of construction.

MSR lumber was introduced in the 1960s for use in demanding, highstrength engineered applications. Today, an estimated 50Vo of all truss manufacturers use MSR in at least part of their production.

MSR lumber is the only engineered wood that is both visually graded and machine evaluated. There are several factors that have pushed MSR annual demand beyond the 1 billion bd. ft. mark: o More specifiers are requiring high performance lumber with strength values that are more reliable and accurate than visual inspection alone. a Engineered truss systems today push structural lumber elements closer to the limit of their design capacity. o Unlike visually graded lumber that can vary from one plant to another, the quality of electronically tested MSR lumber is said to be consistent throughout the industry.

The MSR Lumber Producers Council surveyed suppliers, builders and truss manufacturers to determine their present and future requirements for MSR lumber. Among their comments:

"Our sales of MSR lumber are increasing each year, and it now represents about 40Vo of our total volume," said Chuck Freeland, Boise Cascade. Boise. Id. "Truss manufacturers like the fact that it has higher design values, giving it an extra edge for longer span applications. For example, it's frequently used for clear-span attic trusses to support bonus rooms over a garage without posts or columns. The in-place cost of MSR is very competitive, because in many cases you can use smaller truss chords than you would need for visual grades on the same spans."

Barnett Lumber Co., Denver, Co., uses MSR lumber for top and bottom chords on all of their trusses. "We can't rely on visually graded lumber anymore," explained truss plant mgr. Dennis Wilson. "Since more lumber producers are now offering MSR, the availability has greatly improved. Our customers like the predictability and reliability of MSR."

Added Ed McCormick, Silver State Components, Las Vegas, Nv.: "With trusses made from MSR lumber, you don't need pickup crews that go out and repair trusses at the jobsite. In today's society where there are lawsuits everywhere, MSR means security and reliability. We've used it for 17 years."

According to David Spates, Spates Fabricators, Palm Springs, Ca., "We use MSR lumber for I007o of our truss chords. In this desert climate, green lumber is subject to twisting and waning, but MSR is light, dry and easy to handle. We call it our 'problem solver' because there are no callbacks because of crooked ceilings or truss failure. Even though MSR costs more than visual grades, it pays for itself because it greatly reduces falldown compared to green framing. The key words for MSR are consistency and less liability, because every piece is tested twice."

TimberTech, a major lumber and engineered wood supplier to retail dealers, truss companies and other wholesalers throughout the Southwest, has been using MSR lumber for its truss chords for 25 years.

"Our customers expect it," said Gary Weaver. "MSR provides better uniformity and straightness compared to visual grades. Homebuilders and home buyers are getting more qualityconscious. 'Wavy ceilings' caused by uneven drying of green lumber roof trusses are no longer acceptable. To us, MSR means more reliability, less downfall, more confidence and extra insurance from an engineering standpoint."

TimberTech's inventory includes over 2 million bd. ft. of lumber-8O7o of ir MSR.

Continental Homes, a major TimberTech contractor customer, says they prefer MSR lumber floor and roof trusses. "The lumber is straighter, with less knots and wane and this means fewer call-backs," says Continental's Terry Boech.

As lumber passes through an MSR machine's mechanical grading system, the stiffness or density is measured along the length of each piece. This information is used (along with other properties) to assign or predict key structural properties such as bending strength, tensile strength and modulus of elasticity. Predetermined machine settings help classify lumber into strength categories. After visual elimination by trained graders, final grade selections are made and pieces are placed into common MSR grades such as 1650f-1.5E or 2400f-2.08.

In a proof loader, lumber is loaded possible with visually graded lumber. This means architects, engineers and building designers can be assured of a product with consistent strength properties. Truss designers can build trusses that match the size and strength of lumber components to the desired span. to 2.1 times its assigned design bending stress. This off-line testing helps ensure that machine settings are selecting lumber that meets structural requirements.

Since each piece is non-destructively evaluated and strength and stiffness are monitored on a daily basis, MSR lumber can be expected to meet design requirements with greater confidence and reliability.

MSR has become an international product, since it is now available in several wood species groups, including spruce-pine-fir, southern pine, Douglas fir and hem-fir.

The National Design Specification for Wood Construction lists two broad classes of mechanically graded lumber, Machine Stress Rated and Machine Evaluated Lumber.

The result is said to be a more precise evaluation of each oiece than is

Several factors have pushed MSR annual demand over the 1 billion board foot mark.