Understanding the Importance of Subfloors

Rod Lorenz

One of the most important parts of a building's structure is its floor system. The floor system carries the weight of the roof, interior walls, furniture, finished flooring, appliances, and people..How well the floor structure is built and designed will determine how much weight the floor will be able to carry.

Every flooring system has multiple layers: underlayment, structural joists, surface flooring and, vitally, the subfloor. Some kind of subfloor is found underneath every type of floor. Choosing the right material for the subfloor and correctly installing it is essential to a great floor that performs well and lasts for a long time. 

The term subfloor can sometimes be incorrectly used to refer to the thin layer of cement board, plywood, or even foam padding that lies just under the surface floor covering. The underlayment is actually made of these materials.

The subfloor is a sturdy structural layer that rests directly on the joists. It's usually made of oriented strand board (OSB) or plywood. The subfloor makes a stable surface, not only for floor coverings but also for all of the heavy "live-load" in the living space elements, such as people, kitchen and bath cabinets, furniture, showers, and tubs. Although joists have side bracing, the subfloor can also act as additional bracing to control the joist's lateral movement.

Recommendations for Hardwood Flooring

The place where you are laying a new subfloor and the surface floor covering may affect how the subfloor should be installed. For hardwood flooring installation, plywood is the best subfloor. CDX plywood that's 3/4" thick and rated A/C will serve well for any flooring installation (The first letter in A/C refers to the exposed face grading, and the second letter is the grading of the bottom side.) Tongue-and-groove plywood helps the subfloor fit together better and reduce squeaks.

Weak foundation footings, undersized and/or improperly spaced floor joists, improperly spaced support columns, or weak improperly nailed subflooring can lead to many issues such as:

  • Excessive wear on high spots
  • Uneven spots
  • Unsightly surface variations
  • Decreased lifespan
  • Sagging
  • Excessive movement and shifting
  • Damage
  • Separation
  • Decreased comfort when walking.

These issues can worsen with time and end up requiring reinstallation or repair of part of or all of the flooring.

Would you like to talk with us about hardwood floors? We’re here to help. Contact us at 920-984-3383, 800-354-9902 or info@ralphshardwood.com. Showroom appointments are available.

Image: Shutterstock

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