Most trusses are fabricated using visually graded lumber and machine stress-rated lumber. Visual grades used in chords will include Select Structural, No.1/No.2, whereas webs can also use No. 3 and Stud grades. When calculated stresses and truss configurations require greater strength qualities machine stress-rated lumber is used. Trusses are fabricated using 38 x 64mm to 38 x 286mm lumber according to loading and truss spacing. All trusses for use in Canada must be manufactured using NLGA graded lumber that have assigned structural properties listed in CSA O86-01.
Today, almost all light frame trusses are connected by means of galvanized steel plates referred to commonly as truss plates or connector plates. The plates are manufactured by high speed stamping machines that punch out the plate teeth, and shear the plate to required size. Many sizes and gauges of connector plates are manufactured to suit a variety of joint geometries and loadings. The use of metal plates permits the plant fabrication of trusses with consistent and dependable engineering properties.
The metal connector plate transfers loads between adjoining members through the connector plate teeth. The connector plate strength is dependent on the grip of the teeth and the shear and tensile capacity of the steel plate. The plate is prevented from deforming during installation, and the minimum tooth penetration must be maintained, as monitored by the manufacturer's quality assurance personnel. Each plate must be installed using specifically designed press or roller truss plate equipment to achieve published design values as per CCMC reports. Truss plates that are available to the public through retail outlets or those used by related industries in packaging & pallets will perform to published values only if installed correctly.
In Canada truss plates are usually stamped from 16, 18 or 20 gauge (US Standard Gauge) sheet steel of minimum quality as prescribed in the 2001 edition of CSA Standard O86-01, Engineering Design in Wood. Truss plates are proprietary products approved by the Canadian Centre for Materials in Construction (CCMC) each with a unique set of design values. In order to obtain approval, the plates are tested in accordance with CSA Standard S347- M1980 Method of Test for Evaluation of Truss Plates Used in Lumber Joints.
Plate widths can be from 25mm (1") to 300mm (12") and lengths can be up to 600mm (2') or even longer. Stamping results in teeth lengths varying from about 6mm (1/4") to 25mm (1"). Nail-on plates are occasionally provided to allow assembly by the builder on the site. For example, nail on plates are sometimes used to join separate parts of a field-assembled truss.