Modulus of Elasticity (MOE)
Modulus of Elasticity (MOE) is a measure of a material stiffness — how much it resists bending under load. In lumber and engineered wood, MOE is expressed in millions of pounds per square inch (psi) and determines how far a beam or joist will deflect under a given load. Higher MOE means less deflection.
In Detail
MOE is the single most important structural property for beams and joists because it directly controls deflection — the amount a member bends under load. Building codes set deflection limits (typically L/360 for floors and L/240 for roofs) to prevent bouncy floors, cracked finishes, and visible sag. A member with higher MOE will deflect less under the same load and span.
For dimensional lumber, MOE varies significantly by species and grade. Douglas Fir-Larch No. 2 has a published MOE of 1.6E (1,600,000 psi), while Southern Pine No. 2 has 1.4E. SPF (Spruce-Pine-Fir) No. 2 is 1.4E. Machine Stress Rated (MSR) lumber is graded primarily by its measured MOE, giving more reliable stiffness values.
Engineered lumber achieves higher and more consistent MOE values because the manufacturing process distributes natural defects: LVL ranges from 1.5E to 2.1E, PSL is typically 2.0E, and glulam ranges from 1.5E to 1.9E depending on the layup. I-joist stiffness is expressed as EI (MOE times moment of inertia) because the composite cross-section makes simple MOE comparisons misleading.
Related Terms
Deflection Limit
A deflection limit is the maximum amount a structural member (beam, joist, or rafter) is allowed to bend under load, expressed as a fraction of the span length. Common limits are L/360 for floors (1 inch of deflection per 360 inches of span) and L/240 for roofs. Deflection limits prevent bouncy floors and cracked finishes.
Laminated Veneer Lumber (LVL)
Laminated Veneer Lumber (LVL) is an engineered wood product made by bonding thin wood veneers together with all grain running parallel, creating a beam material that is stronger, straighter, and more dimensionally stable than solid sawn lumber of the same size.
Parallel Strand Lumber (PSL)
Parallel Strand Lumber (PSL) is an engineered wood product made by bonding long, thin strands of wood veneer together under heat and pressure, with all strands oriented parallel to the length. PSL is used for heavy-duty beams, headers, and columns where high strength and stiffness are required.
Related Materials
LVL (Laminated Veneer Lumber)
Laminated veneer lumber (LVL) is a high-strength engineered wood product made from thin wood veneers bonded with structural adhesive under heat and pressure. It is the most commonly specified engineered beam and header material in residential and light commercial construction.
PSL (Parallel Strand Lumber)
Parallel strand lumber (PSL) is a high-strength engineered wood product made from long, thin strands of wood veneer bonded with waterproof adhesive under high pressure. Known commercially as Parallam PSL (Weyerhaeuser), it is used for beams, columns, and posts where maximum load-carrying capacity is required.
Glulam (Glued Laminated Timber)
Glulam (glued laminated timber) is a structural engineered wood product made by bonding multiple layers of dimensional lumber with waterproof adhesive. Available in architectural and industrial grades, glulam is used for beams, columns, arches, and exposed structural applications where both strength and appearance matter.