For many homes, 23/32-inch plywood, often sold as nominal 3/4-inch, is a common subfloor choice. But the right plywood thickness for subfloor use depends on the space between the floor joists, the panel rating, and the flooring going on top. A sheet that works for one room may not suit another. Before buying, check your project plans and flooring instructions. Cardinal Lumber offers plywood and building supplies for new floors and home repairs throughout South Louisiana.
Common Plywood Thicknesses for Subfloors
You will often see 23/32-inch plywood used for subfloors because it provides a firm base in many floor systems. Some approved systems with joists spaced 16 inches apart may allow 19/32-inch plywood, depending on the panel rating and finished floor. These sizes are close to 3/4 inch and 5/8 inch, but the labels are not exact matches. Read the thickness printed on the sheet and match it to the project requirements. Buying by a rounded size alone can lead to the wrong choice.
Check the Floor Joist Spacing
Floor joists are the beams beneath your subfloor. Joist spacing means the distance from the center of one joist to the center of the next. Common spacing includes 16, 19.2, and 24 inches. As that gap grows, the plywood has more space to bridge and may need a higher rating or greater thickness. The strength of the joists matters, too. Thicker plywood cannot fix weak or damaged framing. If your project includes framing repairs, review the plans before choosing framing lumber and floor panels.
Read the Plywood Grade Stamp
Thickness tells only part of the story. The span rating on a structural panel shows the support spacing it is rated to handle under stated conditions. On APA Rated Sheathing, a stamp such as 48/24 gives roof spacing first and subfloor spacing second. It does not mean that panel suits every floor with 24-inch joist spacing. The flooring above may have stricter rules. When shopping for plywood and sheet goods, match the grade, thickness, and span rating to the full floor design.
Match the Subfloor to Your Flooring
The finished flooring can change how thick the subfloor needs to be. Hardwood, vinyl, laminate, and tile each have their own base requirements. For example, some hardwood floor systems over joists spaced 24 inches apart call for 7/8-inch panels or an approved two-layer setup. Tile floors need a base that limits bending, along with the layers required by the tile system. Adding cement board does not replace the plywood strength the design calls for. Check the flooring maker’s instructions before placing your material order.
Can Thin Plywood Serve as a Subfloor?
A thin sheet placed over an existing floor serves a different purpose from the main structural layer. Underlayment may help create a smooth surface for certain floor coverings, but it depends on a sound subfloor beneath it. A sheet of 1/4-inch plywood should not be treated as a stand-alone floor spanning open joists. If you uncover thin panels during a remodel, find out what supports them before adding new flooring. Covering a weak base with another thin layer will not solve the underlying problem.
Install the Panels With Proper Support
Even the right thickness needs proper installation. Tongue-and-groove plywood helps support adjoining panel edges, while square-edge sheets may need blocking beneath unsupported joints. Panels should run with their strength direction across the joists, following the panel instructions. Manufacturers commonly call for panel gaps of about 1/8 inch to allow for movement, though edge profiles may have their own spacing details. Use the specified fasteners and adhesive where required. Poor support or loose fastening can leave a thick panel floor feeling uneven or noisy.
Check for Moisture Before Covering the Floor
Before laying new flooring, check for moisture damage, soft spots, swollen edges, and loose panels. In South Louisiana, leaks and damp crawl spaces deserve attention before the floor is covered. Fix the moisture source and allow materials to dry as required by the flooring maker. Exposure 1 plywood can handle some moisture during construction, but it is not made for ongoing wet conditions. For subfloor repairs, damaged sheets may need replacement rather than another layer placed over them.
Get the Right Plywood for Your Project
Choosing plywood starts with a few clear details: joist spacing, panel rating, finished flooring, and the condition of the existing floor. Bring those details, along with your plans and room measurements, when you shop. As a Lumber & Building Supplier in Louisiana, we can help you review available materials against your project list. Ready to order supplies for a new subfloor or repair? Contact our Patterson building supply team to discuss your materials and request an estimate.