What thickness plywood do I need for 16-inch joist spacing?

23/32" (sold as 3/4") plywood with a 48/24 span rating is the standard recommendation for 16" OC joists. While 19/32" (5/8") meets minimum code, the upgrade to 3/4" significantly improves floor stiffness and squeak prevention.

Is OSB or plywood better for subfloor?

Both are code-accepted and perform similarly in dry conditions. Plywood handles moisture better (doesn't swell at edges) and is slightly better for high-moisture areas. OSB saves $5-10 per sheet and is the builder's standard in most residential construction.

Do I need T&G subfloor panels?

T&G panels are required when joist spacing is 19.2" or 24" (to eliminate the need for edge blocking). For 16" OC joists, T&G is optional but highly recommended as it prevents panel edge movement and squeaking.

How much construction adhesive should I use under subfloor panels?

Apply a 3/8" bead of subfloor adhesive in a wavy pattern along each joist before setting the panel. One 28 oz tube covers approximately 50 linear feet of joist.

Article

Flooring

Best Plywood for Subfloor: Thickness Guide and Grade Comparison

Tom Rodriguez, General Contractor Jul 29, 2024 8 min read

Best Plywood for Subfloor: Thickness Guide and Grade Comparison

The subfloor is the unsung hero of your home — it bears every step, supports your finished flooring, and connects everything to the framing system. Get it right and you'll never think about it again. Get it wrong and you'll hear every step and feel every bounce.

Understanding Subfloor Panel Ratings

Plywood and OSB panels for subfloors carry a span rating stamped on every panel. The rating looks like this:

48/24

First number (48): Maximum spacing between roof rafters or framing if used as roof sheathing (in inches)
Second number (24): Maximum joist spacing when used as subfloor (in inches)

So a 48/24 panel can span 24-inch joist spacing as a subfloor.

Additionally, panels carry an APA (American Plywood Association) Performance Category designation that replaced the old thickness system:

Category 19/32" corresponds to older 5/8" designation
Category 23/32" corresponds to older 3/4" designation
Category 7/16" corresponds to older 7/16" designation

Thickness Guide by Joist Spacing

|---------------|--------------------------|-------------|--------------------|

| 12" OC | 19/32" (5/8") | 19/32" | 40/20 |

| 16" OC | 19/32" (5/8") | 23/32" (3/4") | 48/24 |

| 19.2" OC | 19/32" (5/8") | 23/32" (3/4") | 48/24 |

| 24" OC | 23/32" (3/4") | 7/8" | 60/32 |

| 24" OC + hardwood floor | 7/8" | 1-1/8" | 60/32 |

Rule of thumb: Always use 3/4" (23/32") plywood for 16" OC joists. It's the near-universal standard and only adds $8–12 per sheet vs. 5/8".

Plywood Grades for Subfloor

Structural 1 (STRUCT 1)

Highest shear strength, used in seismic and high-wind zones. More expensive than standard, not necessary for most residential subfloors.

Rated Sheathing (CDX)

The standard subfloor grade. The "CDX" designation means:

C: Face veneer grade (some knot holes, repaired, acceptable face)
D: Back veneer grade (rougher, more defects acceptable)
X: Exterior glue (moisture-resistant bond — not waterproof, but the glue bond survives occasional moisture)

CDX is the standard residential subfloor panel and what most builders use.

Tongue and Groove Subfloor (T&G)

Available in 23/32" and 1-1/8" thicknesses. The T&G edge eliminates the need for blocking at panel edges and prevents the common edge-racking issue. Required by many building codes for certain joist spacings.

Strong recommendation: Use T&G subfloor panels whenever possible. The investment (typically $3–5 more per sheet) prevents squeaky floors and panel movement.

Underlayment Grade

A smooth-faced panel with a B or better face grade. Used over subfloor to provide a smooth surface for resilient flooring (vinyl, LVP). Thinner: typically 1/4" to 3/8".

Plywood vs OSB for Subfloor

Oriented Strand Board (OSB)

Price: $5–10 less per sheet than comparable plywood

Stiffness: Comparable to plywood

Moisture resistance: MORE sensitive to moisture than plywood — swells at edges when wet

Squeak potential: Similar to plywood when installed correctly

Code acceptance: Fully code-accepted for subfloor applications

Plywood

Price: $5–10 more per sheet

Stiffness: Comparable to OSB

Moisture resistance: Better — dries more uniformly without permanent edge swelling

Squeak potential: Slightly better long-term performance

Code acceptance: Fully code-accepted

Verdict: In dry interior applications (typical homes), OSB saves money with minimal performance difference. In crawl space homes, basements, or bathrooms where moisture exposure is higher, plywood is the better investment.

Installation Best Practices

Orientation

Install panels with the strength axis (long dimension and face grain direction) perpendicular to the joists. The span rating is calculated assuming this orientation.

Gaps

Between panels: Leave 1/8" gap between all panel edges. This gap accommodates expansion and prevents buckling. Some T&G panels have this gap built into the joint.

At walls: Leave 1/2" gap at walls for expansion.

Fasteners

For 3/4" subfloor panels on 16" OC joists:

Nails: 8d ring-shank nails, 6" OC at edges, 12" OC in field (or per local code)
Screws: 2-1/2" coarse-thread subfloor screws — better squeak prevention than nails
Adhesive + fasteners: Apply construction adhesive (Liquid Nails SubFloor or equivalent) in a wavy bead on each joist before laying the panel. This dramatically reduces squeaking by preventing the panel from moving against the joist.

Squeak Prevention Protocol

1. Apply construction adhesive to every joist before panel placement

2. Use ring-shank nails or screws (not smooth nails)

3. Leave proper expansion gaps

4. Don't allow panels to sit wet before installing flooring

Special Situations

Radiant heat systems: Use 3/4" plywood (not OSB) for radiant heat subfloors. The thinner construction and lower moisture tolerance of OSB make it less suitable. Leave 1/4" expansion gaps between panels.

Tile installation: Tile requires a very stiff subfloor. For tile over a wood subfloor, total subfloor thickness should be at least 1-1/8" (3/4" subfloor + 3/8" cement board or 1-1/8" single-layer T&G). The Tile Council of North America recommends L/360 deflection limit — meaning the floor should deflect no more than 1/360 of the span under load.