Demonstration of Hardwood Trusses in Residential Construction Projects

Abstract

The hardwood lumber industry is a key component of the forest products industry in the Lake States and Northeast regions of the United States. Two of the primary lumber species include sugar maple (Acer saccharum) and red maple (Acer rubrum). High grade lumber from these species has an extremely high value, often exceeding $1,500/thousand board feet (M bdft). Lower grades of maple including pallet lumber usually sell for $200 to $275/M bdft. A cooperative Lake States research team developed the technical and economic background necessary for using low grade maple as structural components in metal-plate trusses and prefabricated wood I-joists. Specific projects that have been completed addressed the following research topics: lumber yield and recovery, lumber properties, acce\erated drying schedules, truss plate fasteners, truss fabrication and testing, I-joist fabrication and testing, and :financial assessments. An important step prior to implementation was the development of several demonstration projects using structurally graded maple lumber. A relationship was established with the Duluth Chapter of Habitat for Humanity International and a demonstration project was developed to use the red maple lumber in trusses for two houses with attached garag~s that were to be built during the summer of 2001. To minimize concerns oflumber length and s_pecies, we chose to use red maple as truss webs with spruce-pine-fir (SPF) chords in the house section and red maple for both the truss chords and webs in the attached garage. Red maple cants were obtained, sawn into 2- by 4-in. dimension lumber and dried using an accelerated kiln schedule. Structural grading was completed using an E-computer with visual overrides for #2 a11d #3 grade lumber. Truss designs were completed and sealed by a professional engineer and the trusses were manufactured by Kylmala Truss in Duluth, Minnesota. Natural Resources Research Institute (NRRI) personnel were involved in the setting of the trusses. There were no specific problems noted from the use of red maple in either the house or garage trusses. A second demonstration project was designed to use sugar maple lumber as web stock in a standard storage truss in a garage built in rural Duluth, Minnesota. Kiln-dried hard maple remaining from earlier projects was graded using a commercial E-computer. The lumber was then provided to Kylmala Truss for use in manufacturing a 6:12 pitch garage truss that spanned 26 ft. The trusses were set by NRRI personnel and covered with oriented strandboard (OSB) sheathing. There were no specific problems or challenges identified from using hard maple in the trusses, although it was difficult to hand nail siding to the hard maple web on the gable end trusses.