Flooring
Subfloor
The subfloor is the structural layer beneath finished flooring, providing the foundation for all floor coverings. In residential construction, subfloors are typically plywood or OSB over floor joists; in commercial and basement applications, concrete slabs serve as subfloors.
Subfloor condition directly impacts finished floor performance—unevenness telegraphs through, moisture problems transfer upward, and squeaks originate from loose connections. Proper subfloor preparation before installing finished flooring prevents costly problems later.
Key Characteristics
- ✓Structural foundation
- ✓Plywood, OSB, or concrete
- ✓Must be flat and sound
- ✓Affects finished floor performance
- ✓May require leveling
- ✓Should be dry before installation
Types & Variations
Plywood subfloor (wood construction)
OSB subfloor (economical)
Concrete slab (basements, commercial)
Gypcrete (over radiant)
Sleeper system (over concrete)
Works Well With These Styles
Placement & Usage Tips
Test concrete subfloors for moisture before installing wood or laminate products. Repair squeaky plywood by securing to joists. Level depressions with self-leveling compound.
💡 Pro Tip
A 10-foot straightedge reveals subfloor flatness—variations over 3/16 inch in 10 feet should be addressed before installing most flooring. This single check prevents most flooring failures.