What Size LVL to Span 20 Feet: Sizing Guide

Laminated Veneer Lumber (LVL) is an engineered wood product widely used for beams and headers in residential and light commercial construction. When askingwhat size LVL to span 20 feet, the answer depends on load conditions, deflection limits, and building codes. Proper sizing ensures structural integrity for floors, roofs, or open spaces, preventing sagging or failure. This guide explains the key factors and steps for determining the right LVL size.

Key Factors in LVL Beam Sizing

LVL beam size is determined by several variables beyond just the 20-foot span:

• Span length: Clear distance between supports, here 20 feet (240 inches).
• Loads: Dead load (structure weight, e.g., 10-20 psf) and live load (occupants, snow, e.g., 40 psf floors or 20-60 psf roofs).
• Tributary width: Area supported by the beam, affecting total load.
• Deflection limits: Typically L/360 for live load (span/360) or L/240 total, where L is in inches.
• LVL grade: Common types like 1.8E, 2.0E (modulus of elasticity in million psi), or 2.0E-3100F (bending stress in psi).
• Spacing and plies: Multiple plies (e.g., 2x or 3x) increase capacity.

Building codes like the International Residential Code (IRC) require spans to meet these criteria. Always verify with local codes or a structural engineer.

Step-by-Step Sizing Process

Follow these steps to findwhat size LVL to span 20 feet. Use manufacturer span tables (e.g., from LP, Boise Cascade) for precision, or approximate with formulas.

1. Calculate total load:
   Total uniform load (w) = dead load + live load, in pounds per linear foot (plf).
   Example: Floor beam, 40 psf live + 10 psf dead, tributary width 12 ft.
   w = (40 + 10) psf × 12 ft = 600 plf.
2. Check bending stress:
   Maximum moment M = (w × L²)/8, where L = 20 ft.
   M = (600 plf × 20²)/8 = 30,000 lb-ft (360,000 lb-in).
   Required section modulus S = M / Fb, where Fb is allowable bending stress (e.g., 2600 psi for 2.0E LVL).
   S = 360,000 / 2600 ≈ 138 in³.
3. Check shear and deflection:
   Shear V = wL/2 = 600 × 20 / 2 = 6,000 lbs.
   Deflection δ = (5 w L⁴)/(384 E I) ≤ L/360.
   E = modulus of elasticity (e.g., 2.0 × 10⁶ psi); I = moment of inertia.
4. Select size from tables:
   For a 20 ft span floor beam (600 plf, L/360 deflection):
   - Single 1¾" × 14" 2.0E LVL: Max span ~16-18 ft (insufficient).
   - 2-ply 1¾" × 16" 2.0E: ~19-21 ft (viable).
   - 3-ply 1¾" × 11⅞": ~20 ft under lighter loads.
   Roof beam (300 plf): 1¾" × 14" may suffice for simple gable.
5. Convert units if needed:
   Imperial units dominate U.S. construction (feet, inches, psf), but metric users convert via tools.
   20 feet = 6.096 meters.
   600 plf = 895 kg/m (plf × 1.488).

Example calculation: For the 600 plf floor beam, a 2-ply 1¾" × 16" LVL (S ≈ 160 in³ per ply, total 320 in³) exceeds requirements, with I sufficient for deflection under 0.67 inches (L/360 = 0.67 in).

Practical Applications and Common Mistakes

In practice, LVL spans 20 feet in garage door headers, floor beams over basements, or roof ridges. Residential floors often use doubled LVL at 16" spacing; commercial may need deeper sections like 18"-24".

Common pitfalls:

• Ignoring point loads (e.g., walls above).
• Overlooking wet service conditions (reduces capacity 20-30%).
• Not converting units accurately in mixed imperial/metric projects.
• Exceeding simple span tables without engineering review.

For complex loads, software like beam design tools or Excel calculators help, inputting converted units precisely.

Summary

Determiningwhat size LVL to span 20 feetrequires balancing loads, deflection, and grade—typically 2-3 plies of 14"-18" deep 1¾" LVL for standard residential use. Consult span tables and professionals for safety. Use the free unit converter at HowToConvertUnits.com for quick conversions like feet to meters or psf to kPa in your beam calculations.