How to Choose the Best Plywood for Subflooring

Choosing the best plywood for flooring is more than just picking a sheet of wood and laying it down. The subfloor serves as the backbone of your entire flooring system the hidden layer that bears all the weight and stress from above, supporting your floor finish, furniture, and foot traffic. Ignoring this critical layer or selecting the wrong type of plywood can lead to squeaking floors, uneven surfaces, premature floor damage, and costly repairs.

In this comprehensive guide, we will dive deep into everything you need to know about plywood for flooring: the types of plywood suitable for subfloors, the impact of plywood grading and thickness, moisture resistance considerations, comparisons with alternative materials, and detailed installation tips. By the end of this article, you will be empowered to confidently select the best plywood for your flooring project, ensuring a stable, durable, and long-lasting floor.

What Is a Subfloor and Why It Matters

The Subfloor: The Structural Foundation Beneath Your Feet

The subfloor is the foundational layer installed directly over the floor joists the horizontal structural beams that span across your home’s foundation or framing. Unlike the visible floor finishes like hardwood, laminate, or tile, the subfloor is hidden but performs a vital function. It acts as the primary structural surface that supports the entire floor system and all the loads placed on it.

Its main purpose is to create a flat, stable platform that evenly distributes weight across the joists, preventing sagging, bouncing, or flexing. If the subfloor is weak or uneven, the finish flooring will reflect those imperfections leading to cracking tiles, squeaking hardwood, or uneven carpet surfaces. The stiffness and strength of the subfloor material are essential to avoid these issues.

Choosing the best plywood for flooring means prioritizing plywood that can withstand heavy foot traffic, furniture loads, and dynamic forces without bending or deteriorating over time. This layer must be reliable and structurally sound to ensure the longevity of your entire flooring system.

Subfloor vs Underlayment: Clearing Up the Confusion

A common misconception is to confuse the subfloor with the underlayment. While both are layers beneath the finished floor, they have very different roles.

• Subfloor: This is the thick, structural panel usually plywood or oriented strand board (OSB) installed directly onto the floor joists. Its purpose is load-bearing and providing rigidity.
  
• Underlayment: Installed on top of the subfloor, this thinner layer smooths out minor imperfections and creates a suitable surface for the finish flooring. It can also provide moisture barriers or soundproofing depending on the material.
  

When selecting plywood, it’s important to focus on the subfloor layer because it requires strength and thickness. Underlayment plywood does not need to meet the same structural standards and is generally thinner and less robust.

Understanding this distinction helps ensure you buy the correct plywood for flooring structural plywood for the subfloor, and separate materials for underlayment if needed.

Why a Strong Subfloor Makes or Breaks Your Floor

The subfloor’s quality determines not only the structural integrity but also the comfort and sound characteristics of your finished floor. A properly constructed subfloor:

• Prevents Sagging and Flex: The right plywood thickness and quality reduce deflection under weight, keeping the floor firm.
  
• Eliminates Squeaks: Secure fastening methods combined with rigid plywood reduce movement that causes annoying noises.
  
• Supports Heavy Loads: Strong plywood resists denting and damage when heavy furniture or appliances are placed on the floor.
  
• Ensures Flatness: Critical for finish materials like tile or hardwood, even small dips or waves in the subfloor can cause cracks or buckling.
  
• Handles Moisture Risks: Moisture-resistant or treated plywood can protect the subfloor in humid areas or locations prone to spills.
  

If you use substandard plywood or plywood not rated for flooring, you risk costly problems such as warped floors, squeaking, mold growth, or structural failures down the line.

Therefore, selecting the best plywood for flooring suited to your environment and usage requirements is fundamental to a successful flooring project.

Best Types of Plywood for Subfloors

Structural Plywood: Built for Strength and Stability

Structural plywood is engineered specifically to meet the demands of load-bearing flooring applications. Unlike decorative plywood that focuses on surface appearance, structural plywood is manufactured with multiple thin veneer layers glued crosswise with waterproof adhesives. This cross-grain construction enhances the panel’s strength, rigidity, and resistance to bending.

Additionally, structural plywood panels are graded and stamped by organizations like the APA (The Engineered Wood Association), certifying their compliance with building codes. These ratings indicate the panel’s thickness, span rating, and load capacity, helping you select plywood that matches your floor joist spacing and load requirements.

When buying plywood for subfloors, always check for structural grades to ensure the panel can reliably support your floor system for decades without failure.

CDX Plywood: The Industry Standard for Subfloors

CDX plywood is one of the most popular plywood types for subflooring, especially in residential construction. The designation “CDX” refers to the veneer grades and adhesive used:

• The “C” and “D” denote the quality of the face and back veneers; “C” is a smoother, more uniform face veneer, while “D” is rougher with knots and defects.
  
• “X” means the plywood uses exterior-grade glue, which provides superior moisture resistance compared to interior-grade adhesives.

CDX plywood provides a strong balance of durability, affordability, and water resistance, making it the go-to choice for most builders. However, if you’re installing flooring in very moist environments, you may want to consider higher-grade or pressure-treated options for enhanced protection.

Tongue and Groove Plywood: Locking the Floor Panels Together

Tongue and groove plywood differs from standard square-edge plywood because its edges are shaped to interlock:

• Each panel has a “tongue” (a protruding edge) on one side and a matching “groove” (a recessed edge) on the opposite side.
  
• During installation, the tongue fits tightly into the groove of the adjacent panel, locking them together.

This design reduces the movement between panels and helps prevent floor squeaks and panel shifting. It also distributes loads more evenly across the floor surface, especially helpful when joists are spaced wider apart (16” or 24” on center).

Choosing tongue and groove plywood for subflooring can increase the overall stability and longevity of your floor.

Treated vs Untreated Plywood: Tackling Moisture and Durability

Moisture exposure is a major threat to plywood’s integrity. Untreated plywood is susceptible to swelling, warping, delamination, and mold growth if exposed to humidity, leaks, or spills.

To counter this, you can choose:

• Pressure-treated plywood: This plywood is chemically treated to resist rot, insects, and fungi. It’s the best option for crawl spaces, basements, bathrooms, or any area prone to moisture.
  
• Moisture-resistant plywood: This type uses specialized adhesives and coatings that improve water resistance without harsh chemicals.

Using treated or moisture-resistant plywood in vulnerable areas protects your subfloor from premature failure, prolonging the life of your entire flooring system.

Plywood vs OSB for Subfloors: Which Is Better?

Strength and Durability: Battle of the Panels

When deciding on the best plywood for flooring, many homeowners and builders ask whether plywood or OSB (Oriented Strand Board) is the better choice for subfloors. Both materials are engineered wood products designed for structural use, but they have distinct differences in terms of strength and durability.

Plywood is made by gluing together thin layers of wood veneer with alternating grain directions. This cross-grain construction imparts excellent strength, stiffness, and resistance to warping. Plywood tends to maintain its shape better over time and can handle heavy loads without bending or sagging.

OSB, on the other hand, is manufactured by compressing wood strands with adhesives into large panels. While OSB panels have good strength and are often less expensive than plywood, they are generally heavier and can be less resistant to moisture. OSB can swell along the edges when exposed to water, causing uneven subfloor surfaces or even structural weakening.

For high-traffic areas or installations requiring superior durability, plywood’s consistency and rigidity often make it the preferred choice. If you want the best plywood for flooring in terms of long-term performance, plywood usually outperforms OSB.

Moisture Resistance: Which Material Holds Up Better?

Moisture exposure is a critical factor when selecting subfloor materials. Subfloors are often exposed to humidity, spills, and leaks during and after construction. This makes moisture resistance essential to avoid swelling, mold, or delamination.

Plywood generally handles moisture better due to the waterproof adhesives used between the veneer layers and its natural wood grain orientation. However, untreated plywood can still be vulnerable in persistently damp environments.

OSB is more susceptible to water absorption, especially at panel edges, where swelling can cause floor unevenness or even buckling. Although manufacturers have improved OSB with moisture-resistant resins, it typically requires better job-site protection and faster finishing.

If your project involves moisture-prone areas such as bathrooms, kitchens, or basements, opting for moisture-resistant plywood or pressure-treated plywood will provide greater protection than OSB.

Cost and Availability: Budget vs Performance

Price is always a consideration. OSB panels tend to be less expensive than plywood, making them a tempting option for builders on a tight budget. Availability can also influence the choice, with OSB often stocked in larger quantities at lumber yards.

However, choosing the cheapest option upfront can lead to problems later, such as floor squeaks, warping, and replacement costs. The slightly higher initial investment in best plywood for flooring often pays off in durability, installation ease, and peace of mind.

Many contractors recommend plywood subfloors because they provide consistent quality, better fastening holding, and improved performance key to a floor that lasts.

Recommended Plywood Thickness for Subflooring

Thickness Matters: 1/2″, 5/8″, or 3/4″? What to Choose

One of the most important factors in choosing plywood for subflooring is the thickness. Too thin, and the floor will flex, sag, or squeak under pressure. Too thick, and you may add unnecessary weight and expense.

The most common thicknesses for subfloor plywood are:

• 1/2 inch: This is generally too thin for most residential subfloor applications unless you have very closely spaced joists (12 inches or less). It can lead to floor bounce and squeaks.
  
• 5/8 inch: A middle ground option, often used in remodels or areas with joists spaced at 16 inches on center. Provides adequate stiffness for many floors.
  
• 3/4 inch: The industry standard for new construction, especially for joists spaced 16 or 24 inches apart. Offers excellent rigidity, prevents deflection, and supports heavy loads without movement.

Using the best plywood for flooring means matching the thickness to your joist spacing, expected load, and type of finish floor.

Factors Affecting Thickness: Joist Spacing, Load, and Flooring Type

The ideal plywood thickness depends on several key variables:

• Joist Spacing: Wider joist spacing requires thicker plywood to prevent sagging. For example, with joists 24” apart, 3/4” plywood is strongly recommended.
  
• Load Requirements: Floors that will hold heavy furniture, appliances, or large numbers of people need thicker, stronger subfloors to avoid deflection.
  
• Floor Covering Type: Hard surfaces like tile or stone need a very stiff subfloor to prevent cracking. Thinner plywood under these finishes can cause failure.
  
• Installation Conditions: If the subfloor must be glued and screwed (to reduce squeaks), thickness recommendations may vary slightly.

Always consult building codes and manufacturer specifications when choosing plywood thickness to ensure compliance and durability.

Alternative Subfloor Materials

Oriented Strand Board (OSB): The Economical Alternative

OSB is an engineered wood panel made from compressed wood strands and adhesives. It’s widely used as a subfloor material due to its affordability and availability.

While OSB can be a cost-effective option, especially for large-scale projects, it is generally heavier and more moisture-sensitive than plywood. OSB is less resistant to swelling and edge damage, so it requires proper sealing and fast installation of the finished floor.

Choosing OSB over plywood depends largely on budget, climate, and job-site conditions. In dry climates with rapid construction schedules, OSB can perform well, but plywood still leads for longevity and moisture resistance.

Concrete Subfloors: A Different Animal

In some homes, particularly basements and slab-on-grade constructions, concrete serves as the subfloor.

Concrete subfloors are extremely durable and resistant to moisture, but they have downsides such as coldness, hardness, and the need for leveling before installing finish floors. They also lack the flex that wood-based subfloors offer, which can be important for some flooring materials.

Plywood can be installed over concrete slabs using sleepers or specialized adhesives, combining the benefits of wood subfloors with the strength of concrete.

Engineered Panels: Innovations in Subflooring

Newer engineered wood panels combine various wood fibers and adhesives to create strong, stable subflooring products.

APA rated sheathing, structural composite lumber, and other specialty panels can offer improved moisture resistance, stiffness, and ease of installation. Some engineered panels are designed to minimize squeaks and maximize load-bearing capacity.

While these products can be more expensive than traditional plywood, they may provide superior performance in challenging environments or unique construction projects.

Key Factors in Choosing the Right Subfloor Plywood

Structural Rating and Grade: Decoding the Stamps and Labels

When selecting the best plywood for flooring, one of the most critical steps is understanding plywood grading and structural ratings. Plywood panels are stamped by certification agencies such as the APA (Engineered Wood Association), providing valuable information about the panel’s strength, thickness, grade, and intended use.

The grading system typically consists of letters and numbers for example, «CDX» or «ACX.» The letters indicate the veneer quality on the face and back of the panel, where “A” is the highest quality with minimal defects, and “D” is the lowest, often with knots or imperfections. The “X” usually indicates exterior glue that is more resistant to moisture.

Beyond the veneer quality, structural ratings include span ratings (like 48/24), which tell you the maximum joist spacing the panel is designed to cover safely. The first number refers to roof sheathing, and the second to subflooring applications. For subflooring, the span rating guides you on how thick the plywood should be to avoid excessive deflection or failure.

Choosing plywood with the correct structural rating and grade is essential to guarantee that your subfloor can safely support expected loads and maintain long-term stability.

Moisture and Weather Resistance: Protecting Your Floor’s Foundation

Moisture is the enemy of wood. Even the best plywood can degrade quickly if exposed to prolonged dampness or water infiltration. Therefore, moisture resistance is a key factor in selecting subfloor plywood, especially in climates with high humidity or where floors may occasionally get wet.

Pressure-treated plywood is impregnated with preservatives that protect against rot, fungi, and insects. It is an excellent choice for crawl spaces, basements, and other moisture-prone areas.

In addition, some plywood panels are manufactured with moisture-resistant adhesives and coatings to minimize water absorption. These panels, often labeled as «moisture-resistant plywood,» offer enhanced durability without the chemical treatments of pressure-treated plywood.

Before installation, it’s crucial to ensure that the subfloor is properly sealed and that the building envelope protects the floor from leaks or water intrusion.

Load-Bearing Capacity: Supporting Your Life and Furniture

Your subfloor’s load-bearing capacity directly affects the comfort and safety of your living spaces. Floors endure constant dynamic loads people walking, furniture shifting, appliances vibrating, even heavy equipment in some commercial settings.

The best plywood for flooring will have a high load-bearing capacity, meaning it resists bending and cracking under pressure. Thicker panels with better span ratings improve this capacity. Additionally, fastening methods such as glue and screws, rather than nails alone, help maintain a secure and stiff floor.

Ignoring load requirements can lead to sagging floors, floor squeaks, or even structural damage over time. Therefore, consider the expected load in your space for example, kitchens and living rooms often require stronger subfloor materials than closets or hallways.

Certification or Stamp: Why It Matters

Always check for certification marks such as the APA stamp on plywood. This stamp verifies that the panel meets industry standards for strength, moisture resistance, and safety.

Panels without certification may not provide reliable performance, risking premature floor failure or non-compliance with local building codes.

The APA-rated sheathing, for instance, ensures the plywood meets strict criteria for subfloor use, including thickness, bonding, and mechanical properties.

Buying plywood with proper certification is an insurance policy for your floor’s durability and your home’s safety.

Pros and Cons of Using Plywood for Subflooring

Advantages: Why Plywood Remains a Popular Choice

Plywood offers several compelling benefits that make it the best plywood for flooring in many situations:

• Affordable: Compared to other engineered wood products or specialty materials, plywood is reasonably priced, making it accessible for most budgets.
  
• Durable: Thanks to its layered construction, plywood resists bending, warping, and cracking under normal conditions.
  
• Easy to Install: Plywood panels are lightweight relative to their strength, easy to cut, and install with standard tools.
  
• Good Fastener Holding: Plywood holds nails and screws firmly, reducing squeaks and loosening over time.
  
• Versatile: Available in various thicknesses, grades, and types, plywood can suit almost any flooring project.

These advantages explain why plywood continues to dominate as a preferred subfloor material in residential and commercial construction.

Disadvantages: What to Watch Out For

Despite its strengths, plywood has some drawbacks that must be considered:

• Prone to Water Damage (if untreated): Without treatment, plywood absorbs moisture, leading to swelling, delamination, or rot.
  
• Can Warp or Delaminate Over Time: In harsh environments or poor installation conditions, plywood panels may warp or layers separate.
  
• Not Completely Impervious to Termites or Mold: Untreated plywood is vulnerable to pests and fungal decay if exposed to moisture.
  
• Requires Proper Installation: Without correct fastening and sealing, plywood subfloors can squeak or develop unevenness.

By understanding these potential downsides, you can take appropriate measures such as using moisture-resistant or pressure-treated plywood and following best installation practices to mitigate risks.

Bottom Line: Making the Smart Choice for Long-Lasting Floors

Selecting the best plywood for flooring is a crucial decision that sets the foundation for a durable, stable, and comfortable floor. It requires careful consideration of structural requirements, moisture resistance, thickness, and certification.

Using high-quality structural plywood like CDX or tongue and groove panels, matched with appropriate thickness and moisture protection, ensures your subfloor performs well under load and over time. While alternatives like OSB or concrete exist, plywood’s proven track record and versatility make it a reliable choice for most projects.

In summary, invest time in understanding your project’s needs, consult professional guidelines, and choose plywood with the right grades and certifications. Your floor and your peace of mind will thank you.