Machine stress rated lumber
Machine stress rated (MSR) lumber is a type of softwood dimension lumber evaluated by mechanical stress rating equipment.
MSR lumber differs from visually graded lumber. Each piece is tested and assigned a rating based on its modulus of elasticity (flexibility) to show stiffness and strength.
Traditionally, MSR lumber has been used to make engineered wood products such as roof trusses. It is also used in the production of chords for I-beams and webs in stressed-skin panels.
Other products that use MSR lumber include:
MSR machines non-destructively test each piece of lumber to determine its stiffness so that it can be assigned a permitted design stress. The grading system for MSR lumber is based on the relationship between the stiffness of a piece of lumber and its bending strength.
Grades of MSR lumber are assigned “f-E” values (e.g., 1950f-1.7E). The “f” value shows the predicted strength in pounds per square inch (psi), while the “E” value gives the average stiffness measured in millions of pounds per square inch (106 psi).
Products like roof trusses will use different grades of MSR lumber within their structure, depending on the particular stresses experienced by the chords composing each roof truss. Most MSR lumber is 38mm x 89mm (two-by-four), 38mm x 140mm (two-by six) or 38mm x 184mm (two-by-eight).
- Date modified: