Tfuss specifrers asking for

1/-\NE OF the earliest forms of \-fengineered 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 507o 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 I 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. 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.

. Engineered truss systems today push structural lumber elements closer to the limit of their design capacity.

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

"We've used MSR lumber for our truss chords for 25 years. Our customers expect it. MSR provides better uniformity and straightness compared to visual grades," said Gary Weaver, Timber tech, San Antonio (Cibolo), Tx. "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." erties. Truss designers can build trusses that match the size and strength of lumber components to the desired span.

"We have over 2 million bd. ft. of lumber in our inventory and SOVo of it is MSR," Weaver adds. Timber Tech just celebrated its 25th anniversary as a major lumber and engineered wood supplier to retail dealers, truss companies and other wholesalers throughout the Southwest.

Continental Homes, a TimberTech contractor customer, says they prefer MSR lumber floor and roof trusses.

"The lumber is straighter, with fewer knots and less wane and this means fewer call-backs," says Continental's Terry Boech.

Scott Stanley, Scosta Corp., Sebring, Fl., agreed: "With MSR lumber, we can provide our customers with superior quality trusses that meet and exceed appearance and engineering standards."

According to Randy Smith, Georgia Mountain Components, Oakwood. Ga.. "MSR demand is moving ahead fast because of its improved availability, quality, strength to carry heavier loads, and improved pricing stability. We're increasing our MSR volume each month."

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- l.5E or 24OOf-2.08.

In a proof loader, lumber is loaded 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.

The result is said to be a more precise evaluation of each piece than is possible with visually graded lumber.

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.

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

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.

This means architects, engineers and building designers can be assured of a product with consistent strength prop-