Choosing the right subfloor for hardwood flooring is crucial for ensuring stability, durability, and an optimal finish. Here’s a breakdown of what to consider when selecting the best subfloor:

1. Type of Hardwood Flooring

  • Solid Hardwood: Solid hardwood flooring is more prone to moisture fluctuations, so it requires a sturdy, stable subfloor like plywood or OSB (oriented strand board).
  • Engineered Hardwood: Engineered hardwood is less susceptible to moisture, making it more versatile. It can be installed on concrete subfloors with proper moisture barriers or on wood subfloors.

2. Subfloor Material Options

  • Plywood: A common choice for subfloors, plywood provides durability and dimensional stability. It is typically available in 3/4″ thickness, which is ideal for supporting hardwood floors.
  • Oriented Strand Board (OSB): Another affordable option, OSB offers a solid base but isn’t as water-resistant as plywood. It should be at least 3/4″ thick for stability.
  • Concrete: Concrete is generally used for subfloors in basements or ground-level installations. It requires a moisture barrier, such as a polyethylene sheet or a specialized underlayment, before installing hardwood.
  • Particleboard: Not recommended for hardwood flooring, as it lacks the stability needed and does not hold nails well.

3. Subfloor Thickness

  • Minimum Requirements: For solid hardwood, a minimum thickness of 3/4″ for plywood or OSB is recommended. Thicker subfloors reduce flexing, which can prevent damage to the hardwood above.
  • Engineered Wood Flooring: Engineered hardwood can sometimes be installed on thinner subfloors, but thicker subfloors still enhance stability.

4. Subfloor Moisture Control

  • Moisture Barrier: For concrete subfloors, use a moisture barrier to protect hardwood from absorbing ground moisture. A polyethylene sheet or a special hardwood flooring underlayment works well.
  • Relative Humidity and Moisture Testing: Ensure moisture levels in the subfloor are within 12% of the hardwood flooring. Test the subfloor with a moisture meter to confirm it is dry enough before installation.

5. Installation Method of Hardwood Flooring

  • Nail-Down: Requires a wood subfloor (such as plywood or OSB). Solid hardwoods often use this method and need a sturdy base.
  • Glue-Down: Works for both engineered wood and some solid woods but requires smooth subfloors, such as plywood, OSB, or concrete. In the case of concrete, a moisture barrier is essential.
  • Floating Floor: Floating floors do not attach directly to the subfloor, which makes them suitable for a range of subfloors, including those with minor imperfections. This method is typically used with engineered hardwood.

6. Flatness and Smoothness of Subfloor

  • Level Surface: A flat subfloor is critical for preventing squeaks and uneven spots in hardwood flooring. Check for high or low spots and sand or fill them as needed.
  • Repair Damages: Address any issues like cracks, holes, or uneven areas. For wood subfloors, loose boards should be nailed down, and concrete cracks should be patched with a leveling compound.

Summary Checklist for Choosing a Subfloor:

  • Choose plywood or OSB for wood subfloors, and concrete with a moisture barrier for basement or ground-level installations.
  • Ensure adequate thickness (3/4″ or thicker for stability).
  • Use a moisture barrier on concrete subfloors.
  • Ensure the subfloor is level and smooth to avoid unevenness.
  • Match the installation method to the subfloor type for stability and durability.

Selecting the right subfloor based on the type of hardwood, location, and moisture conditions will help ensure a long-lasting and beautiful hardwood floor.