How thick should the plywood subfloor be for hardwood installation?

For hardwood flooring installation, plywood subfloor thickness should be minimum 5/8" (15.9mm), with 3/4" (19mm) being the preferred standard for optimal stability and performance.

The 3/4" plywood subfloor provides the best foundation for hardwood installation because it minimizes deflection and movement that can cause squeaks, gaps, or premature wear. This thickness works well with both nail-down solid hardwood and engineered hardwood installations. The additional rigidity helps prevent the slight bouncing that can occur with thinner subflooring, which over time can loosen fasteners and create noise issues.

5/8" plywood can work for engineered hardwood or lighter solid hardwood species, but it requires more attention to joist spacing and overall structural support. If your joists are spaced 16" on center or less, 5/8" may be adequate, but 19.2" joist spacing typically requires the full 3/4" thickness. Many experienced installers prefer 3/4" regardless of joist spacing because it provides a more forgiving installation surface and better long-term performance.

In Ottawa's climate with seasonal humidity changes, proper subfloor preparation is critical to prevent movement and gaps. The plywood should be exterior-grade or moisture-resistant, properly fastened every 6-8 inches along joists, and any gaps between sheets should be minimal. Before installation, the subfloor must be flat within 3/16" over 10 feet, clean, and dry (moisture content below 12%).

Check your existing subfloor thickness before ordering materials, as this affects your transition heights to adjacent rooms and may influence your hardwood species selection. A licensed flooring contractor can assess your specific subfloor conditions and recommend any necessary improvements for a successful installation.

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