1 1/8 Lumber in Construction in USA: In-Depth Guide for Builders and Architects

Overview of 1 1/8 Lumber Dimensions in U.S. Construction

1 1/8 lumber plays a specialized yet vital role in modern residential and commercial construction across the United States. Unlike nominal sizes such as 1×6 or 2×4, the 1 1/8-inch thickness falls under more exact engineered wood dimensions used in specific applications requiring greater load capacity, dimensional stability, and long-span performance.

Typically available in plywood sheets, OSB panels, or laminated veneer lumber (LVL) forms, this dimension is essential for meeting structural codes in high-demand zones such as subfloors, roof decks, and multi-layered wall systems.

Standard Applications of 1 1/8 Lumber in Construction Projects

Heavy-Duty Subflooring in Residential Structures

In multi-story residential buildings, 1 1/8-inch subfloor panels are the gold standard. Their increased thickness provides exceptional rigidity, reducing deflection and eliminating the “bounce” often associated with thinner subfloors. Builders prefer this thickness when installing under:

• Hardwood flooring
• Tile and stone surfaces
• Heavy kitchen cabinetry

The result is a floor that feels solid underfoot, minimizes squeaking, and supports longer spans between floor joists.

Commercial Roof Sheathing

In commercial construction, 1 1/8 structural panels are used in roof assemblies where long joist spacing or heavy equipment like HVAC systems demand superior strength. These panels are common in:

• Retail buildings
• Warehouses
• Cinemas and arenas

The added mass and density help reduce vibration transmission and noise, which is beneficial in sound-sensitive environments.

Engineered Stair Treads and Landings

For code-compliant stair assemblies, 1 1/8-inch lumber is often utilized to construct treads and platforms. This dimension meets or exceeds most building code requirements for strength and durability, especially in commercial stairs exposed to high foot traffic.

• Interior stair systems in schools, hospitals, and office buildings
• Exterior landings with weather-treated 1 1/8 LVL for moisture resistance
• Spiral and custom stair installations needing customized milling

Formwork and Concrete Shoring

Contractors engaged in concrete pouring use 1 1/8-inch plywood forms for building walls, columns, and slabs. These forms are capable of withstanding the hydraulic pressure of wet concrete without deforming. They are reusable and offer better dimensional integrity over multiple pours compared to thinner panels.

Material Types Available in 1 1/8 Lumber

Plywood Panels

1 1/8 plywood panels are constructed using multiple veneer layers, bonded with phenol-formaldehyde adhesives under high heat and pressure. These panels are typically available in:

• Tongue-and-groove edges for tight, interlocking seams
• APA-rated panels for structural certification
• 24OC, 32OC, or 48OC ratings based on joist span compatibility

Commonly used plywood types include:

• Southern Yellow Pine Plywood
• Douglas Fir Plywood
• Maple or Birch Plywood for specialty interior finishes

Oriented Strand Board (OSB)

Engineered with compressed wood strands arranged in cross-directional layers, 1 1/8 OSB panels provide consistent strength and cost-effectiveness for:

• Subfloors
• Roof decks
• Wall bracing panels

They are often edge-sealed to reduce swelling from moisture exposure, making them suitable for exterior sheathing when properly installed.

Laminated Veneer Lumber (LVL)

LVL products in 1 1/8 thickness are used for load-bearing headers, rim boards, and beam framing. Their high strength-to-weight ratio and dimensional consistency make them preferable in engineered applications requiring precise tolerances.

Structural Performance and Span Ratings

1 1/8-inch panels are generally rated for 24-inch or wider joist spans, depending on panel type and material composition. Key span advantages include:

• Increased load capacity
• Reduced deflection under concentrated loads
• Superior performance for point loads (e.g., heavy furniture or machinery)

Typical live load capacity exceeds 100 pounds per square foot (psf) for joist spans of 24 inches or less, making it a dependable option in heavy-use zones.

Moisture Resistance and Durability Enhancements

To meet performance requirements in wet or humid environments, 1 1/8 lumber panels are manufactured with moisture-resistant adhesives and treatments:

• Exposure 1 rated panels tolerate moisture during construction delays
• Fully waterproof marine-grade plywood available for specialty applications
• Edge coating systems prevent delamination in exposed edges

Contractors should always seal cut edges and fastener penetrations with appropriate sealants to preserve the panel’s structural integrity.

Fastening Techniques and Installation Best Practices

Installation of 1 1/8 lumber products requires specialized fastening systems due to the panel’s thickness and density:

• Use 2½” or longer ring-shank nails or screws to ensure full penetration into underlying framing.
• For subfloors, apply construction adhesive in combination with fasteners to reduce squeaking and increase bonding strength.
• Stagger panel seams and allow for expansion gaps between panels to accommodate moisture-related movement.

Finishing, Leveling, and Surface Preparation

Before applying final flooring, it’s essential to prepare 1 1/8 subfloor surfaces for optimal adhesion and performance:

• Sand joints or high spots for smooth transitions.
• Fill gaps or surface damage using wood filler or leveling compounds.
• Apply primer or sealers before installing finishes like hardwood or tile.

Proper preparation ensures uniform load distribution, enhances material longevity, and avoids future flooring issues such as cracking or lifting.

Pricing and Sourcing Information

The cost of 1 1/8-inch panels varies based on material type and regional availability. As of 2025, typical pricing includes:

• Plywood (APA-rated): $75–$100 per 4×8 sheet
• OSB Panels: $55–$75 per 4×8 sheet
• LVL boards: $6–$10 per linear foot

Builders should source from certified lumberyards offering APA stamps, mill grade documentation, and on-site storage protection to guarantee product quality.

Compliance with U.S. Building Codes

1 1/8-inch lumber conforms to requirements set forth by:

• International Residential Code (IRC)
• International Building Code (IBC)
• APA – The Engineered Wood Association

All panels used in structural roles must carry grade stamps confirming compliance with:

• Span ratings
• Exposure ratings
• Species and glue classification

Conclusion

1 1/8 lumber provides a robust, dependable solution for load-bearing, flooring, and roofing systems in U.S. construction. Whether in the form of plywood, OSB, or LVL, its thickness delivers superior strength, minimal deflection, and code-compliant reliability across a wide range of structural applications. When properly installed and maintained, it serves as a long-lasting foundation for both residential and commercial building projects.