What Thickness Plywood Should I Use for Flooring?

Plywood thickness plays a crucial role in determining the durability and stability of flooring in both residential and commercial settings. As a versatile and affordable building material, plywood has become increasingly popular due to its inherent strength and ease of installation. To make well-informed decisions when selecting the appropriate plywood thickness for flooring, it is essential to consider factors such as subfloor type, room usage, and weight load requirements.

According to the Engineered Wood Association (APA), the recommended thickness for plywood used in flooring applications typically ranges from 5/8-inch (15.9 mm) to 3/4-inch (19.1 mm). Thinner plywood sheets might result in sagging or buckling, especially in areas with heavy foot traffic or where larger loads need to be supported. On the other hand, thicker plywood offers greater resistance to deflection and can more effectively distribute weight across the floor surface.

In addition, it is important to consider the plywood grade as well, which can directly impact the overall performance and stability of the flooring. The American National Standards Institute (ANSI) has established a grading system for plywood, with grades A to D indicating the quality of the outer veneer. Higher grades, such as A and B, are generally preferred for flooring applications, as they offer smoother surfaces and fewer appearance defects. By taking the time to research and compare various thicknesses and grades of plywood, homeowners and builders can ensure that their flooring projects have a strong and long-lasting foundation.

Fundamentals of Plywood Thickness

Standard Thicknesses

Plywood for flooring is available in various thicknesses, typically ranging from 1/4 inch (6mm) to 1 1/8 inches (28mm). Some common thicknesses include:

• 1/4 inch (6mm)
• 3/8 inch (9mm)
• 1/2 inch (12mm)
• 5/8 inch (15mm)
• 3/4 inch (18mm)
• 1 inch (24mm)
• 1 1/8 inches (28mm)

The appropriate thickness for a specific project depends on factors such as the type of flooring to install, the weight it will bear, and the subfloor’s condition.

Load Bearing Capacity

The load-bearing capacity of plywood varies depending on its thickness. Thicker plywood offers greater support and is better suited for areas with heavy furniture or occupants. The American Plywood Association (APA) provides recommendations for plywood thickness based on the load bearing requirements:

Thickness	Maximum Joist Spacing
5/16 inch	16 inches
3/8 inch	16 inches
7/16 inch	24 inches
1/2 inch	24 inches
19/32 inch	32 inches
23/32 inch	48 inches

Following these guidelines ensures a robust and stable flooring surface that can withstand the demands of everyday usage.

Moisture Resistance

Plywood’s moisture resistance depends on the adhesive used in its production and the various layers’ quality. Exterior-grade or marine-grade plywood is recommended for areas prone to moisture exposure, such as bathrooms and kitchens. These types of plywood feature adhesives with enhanced water-resistant properties, ensuring they maintain their structural integrity in moisture-prone spaces.

It’s essential to choose the right plywood thickness for moisture resistance. For instance, 3/4 inch (18mm) thick plywood is recommended for bathroom flooring to prevent sagging and warping due to humidity and potential water exposure.

By considering the standard thicknesses, load-bearing capacities, and moisture resistance, you can select the most suitable plywood thickness for your flooring project.

Selecting the Right Thickness for Flooring

Residential Applications

In residential applications, a plywood thickness of 1/2 inch or 5/8 inch is commonly used for flooring. This thickness provides a balance of durability, affordability, and ease of installation. A thicker plywood like 3/4 inch may be used in high-traffic areas or where additional insulation is desired.

Commercial Applications

For commercial applications, a plywood thickness of 3/4 inch is often recommended. This thickness offers increased stability, wear resistance, and support for heavier loads. In some cases, a thickness of 1 inch may be used for commercial projects with very high foot traffic or heavy furniture and equipment loads.

Application	Plywood Thickness
Residential	1/2″ or 5/8″
Commercial	3/4″ or 1″
Industrial	1″ and up

Industrial Applications

Industrial flooring applications require even greater strength and durability. Plywood thicknesses of 1 inch and up are necessary to provide adequate support for heavy machinery, vehicles, and other industrial loads. The choice of thickness for industrial flooring will depend on factors such as weight distribution, floor lifespan, and the specific equipment used in the space.

It is essential to consider the specific demands and requirements of each application when selecting plywood thickness for flooring. By taking into account factors such as foot traffic levels, equipment weight, and desired floor lifespan, the appropriate thickness can be chosen to ensure a durable and long-lasting flooring solution.

Plywood Types and Corresponding Thicknesses

Softwood Plywood

Softwood plywood, typically made from trees like pine, spruce, and fir, is often used for construction purposes. Common thicknesses for softwood plywood flooring are:

• 3/8 inch (9.5 mm): Suitable for subfloors and underlayment
• 1/2 inch (12.7 mm): Common for subfloors and roofing
• 5/8 inch (15.9 mm): Good for subfloors paired with thicker floor coverings
• 3/4 inch (19 mm): Often used for single-layer flooring and tongue-and-groove applications

Hardwood Plywood

Hardwood plywood, sourced from deciduous trees such as oak, maple, and birch, is commonly used for flooring, cabinetry, and furniture. Thicknesses for hardwood plywood flooring generally range from:

• 1/4 inch (6.35 mm): Ideal for overlaying existing flooring or countertops
• 1/2 inch (12.7 mm): Suitable for subfloors and thicker floor coverings
• 3/4 inch (19 mm): Typically employed for single-layer hardwood flooring installations

Tropical Plywood

Tropical plywood, manufactured from various tropical wood species, is often favored for its increased water resistance and durability. Flooring thicknesses for tropical plywood typically include:

• 1/2 inch (12.7 mm): Common choice for subfloors in humid environments
• 3/4 inch (19 mm): Preferred for flooring installations in demanding conditions and high-traffic areas

Composite Plywood

Composite plywood combines a thin layer of hardwood or other veneers with a core made of stronger, engineered wood products like medium-density fiberboard (MDF) or particleboard. It offers a cost-effective and stable alternative for flooring applications. Primary thicknesses for composite plywood used in flooring include:

• 1/4 inch (6.35 mm): Recommended for overlaying existing floors or countertops
• 1/2 inch (12.7 mm): Suitable for use as a stable subfloor base
• 3/4 inch (19 mm): Most common choice for installations requiring additional strength and stability

Installation Techniques and Considerations

Subfloor Preparation

Before installing plywood flooring, it’s crucial to prepare the subfloor. Ensure the surface is clean, dry, and free of debris. Remove any protruding nails or screws and repair damaged areas. Level the subfloor using leveling compound if necessary, as an uneven surface can cause problems with the installation. Verify the subfloor’s moisture levels to prevent potential expansion or contraction of the plywood.

Expansion Gaps

Allow space for expansion gaps when installing plywood flooring. Typically, a 1/4-inch gap around the perimeter of the room and between adjacent sheets is recommended. Expansion gaps accommodate the natural movement of plywood due to temperature and humidity changes, preventing potential damage. Use spacers to maintain the consistent gap width during installation.

Adhesives and Fasteners

Selecting the appropriate adhesives and fasteners is critical for a successful plywood flooring installation. Use high-quality wood glue to bond plywood sheets to the subfloor, ensuring proper adhesion. Spread the adhesive with a notched trowel and press the plywood firmly into place.

Fasteners, such as nails or screws, should be evenly spaced and long enough to penetrate the subfloor. For example, a 1/2-inch plywood sheet requires 1-1/2-inch fasteners. Drive fasteners every 6 inches along the edges and every 12 inches in the field. Always countersink fasteners to provide a smooth surface for the finished flooring.

Plywood Thickness Regulations and Standards

International Building Code

The International Building Code (IBC) outlines specific guidelines that must be followed when determining the thickness of plywood for flooring projects. It is essential to adhere to these regulations to ensure a safe and stable flooring system. The IBC suggests a minimum plywood thickness of 15/32 inch for joist spacing up to 16 inches, and a minimum thickness of 19/32 inch for joist spacings up to 24 inches.

Some key factors that the IBC takes into consideration include:

• Load-bearing capacity
• Deflection and bending resistance
• Exposure to moisture and environmental conditions

For exact thickness recommendations and requirements, it is important to consult the official IBC documentation relevant to the specific construction project.

APA Plywood Design Specifications

The APA – The Engineered Wood Association provides detailed design specifications for plywood flooring thickness. These specifications are also widely recognized by the construction industry and are an important reference in determining the appropriate plywood thickness for a given project.

The APA Plywood Design Specifications offer the following guidelines for common flooring applications:

• Single Layer Flooring: A minimum thickness of 15/32 inch for joist spacing up to 16 inches and a minimum thickness of 19/32 inch for joist spacing up to 24 inches.
• Subfloor and Underlayment Combinations: For floors with a separate subfloor and underlayment, the minimum thickness recommendations are as follows:
  • Subfloor: 15/32 inch for 16-inch joist spacing and 19/32 inch for 24-inch joist spacing
  • Underlayment: 1/4 inch minimum

It is worth noting that these guidelines are intended to serve as a starting point, and further consultation with an engineer or architect may be necessary to ensure that the chosen plywood thickness meets the specific requirements of a given project, taking into account factors such as load capacity, span rating, and any unique environmental conditions.