What is the difference between Machine Stress Rated (MSR) lumber and visually graded lumber? – Canadian Lumber Standards Accreditation Board

Q: What is the difference between Machine Stress Rated (MSR) lumber and visually graded lumber?

MSR Grade Stamp Regular Grade Stamp Based upon in-grade testing the anticipated strength properties for visually graded lumber are determined by visually assessing each piece for the presence of strength reducing characteristics such as knots, slope of grain, etc. The strength characteristics of MSR lumber are determined by testing each piece to measure the stiffness. MSR lumber is also visually checked for properties other than stiffness which might affect the piece. Given that the stiffness of each piece is measured individually, MSR lumber can be assigned higher specified design strengths than visually graded dimension lumber. This information will appear on the MSR grade stamp with an Fb and E value. Fb indicates the fibre stress in bending applicable to lumber loaded on edge in pounds per square inch. The Fb values can range from 1200 Fb to 3000 Fb. E is the mean or average modulus of elasticity (MOE) for the grade in millions of pounds per square inch. The E values can range 1.2 E to 2.4 E.

MSR Grade Stamp	Regular Grade Stamp

Based upon in-grade testing the anticipated strength properties for visually graded lumber are determined by visually assessing each piece for the presence of strength reducing characteristics such as knots, slope of grain, etc. The strength characteristics of MSR lumber are determined by testing each piece to measure the stiffness. MSR lumber is also visually checked for properties other than stiffness which might affect the piece. Given that the stiffness of each piece is measured individually, MSR lumber can be assigned higher specified design strengths than visually graded dimension lumber. This information will appear on the MSR grade stamp with an Fb and E value. Fb indicates the fibre stress in bending applicable to lumber loaded on edge in pounds per square inch. The Fb values can range from 1200 Fb to 3000 Fb. E is the mean or average modulus of elasticity (MOE) for the grade in millions of pounds per square inch. The E values can range 1.2 E to 2.4 E.

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