Layered flooring systems are flexible, sturdy, inexpensive, and easy to build. The flooring system found in most homes starts with a floor covering (laminate, vinyl, tile, or other) on top of an optional buffering underlayment. The floor covering and underlayment rest on a thick, solid subfloor supported by sturdy joists.

Learn the differences between subflooring, joists, and underlayment, as well as their roles below floor coverings such as wood, tile, laminate, or vinyl.

Material Vertical Position Purpose Required?
Floor covering 1 Top visual/walking layer Yes
Underlayment Optional buffer No
Subfloor 3 Solid flat base Yes
Joists 4 Main superstructure Yes

Floor Covering

Floor covering is the topmost layer that you see and walk on such as ceramic tile, solid wood, laminate, engineered wood, luxury vinyl, or carpeting. Floor covering is not structural, so it will always have a subfloor under it.

Underlayment

Underlayment is the optional thin buffer between the floor covering and the subflooring.

Underlayment is not required in all installations, and it can have different meanings, such as:

  • Wood: Thin luan or plywood that smooths uneven subflooring for solid hardwood or engineered wood flooring.
  • Backer board: Cement backer board for tile and stone flooring.
  • Laminate underlayment: Thin foam or felt installed under laminate flooring.

Subfloor

The subfloor is the flat, stable surface below the floor covering. The subfloor is nailed to the top of the joists.

Most houses have subfloors. The subfloor is typically made of plywood or OSB, ranging from 19/32 inches to 1-1/8 inches thick. Subfloor plywood or OSB sheets typically have tongue-and-groove edges to reduce floor sagging and bounce.

If the bottom-most floor is a concrete slab, its definition as a subfloor becomes more fluid. The concrete can be painted or left uncoated and used as-is. Or a subfloor system can be built on top of it to separate a floor covering (like carpeting or laminate) from the concrete. A third option is to install an uncoupling membrane like Schluter Ditra on the concrete and then install ceramic tile on top of the membrane.

Joists

Joists form the bottom-most superstructure of the flooring system.

Made of engineered wood, laminated wood, or dimensional lumber, joists are arranged parallel to each other and typically 16 inches apart, though this spacing may vary. If the home has a concrete slab floor, it will not have joists.

Tip

An older home that has been extensively remodeled may have many layers of old and new flooring. Homeowners may have added layer upon layer of flooring rather than stripping away lower layers. Keeping layers in place is valuable when one of those layers contains asbestos. When it is kept in place and undisturbed, asbestos is safe. But sanding, grinding, or scraping asbestos floor layers is hazardous.

How to Determine Flooring Type and Thickness

You may need to determine the number of layers of flooring materials and the floor’s total thickness. You will need a straight-edge ruler or a tape measure to do this.

  • Floor heating vent: Remove a floor HVAC vent by lifting it straight up. With the vent removed, you have a wide, clear view of a cross-section of your floor.
  • Top of stairs: Sometimes, the top of a staircase has an unfinished opening that permits a cross-section view of the entire floor. Even if the stairs are fully finished, you can get an approximate thickness reading by measuring the distance from the top of the riser to the top of the floor covering.
  • Basement and crawlspaces: This method might give you a rough idea of the layers if the basement’s ceiling and joists are exposed. Reach up and try inserting a straight edge or tape measure up through any space or gap you find between the subfloor panels and take note of the measurement.
  • Unfinished areas: If an unfinished area like a closet or pantry lacks baseboard molding, place the straight edge along the wall. Slide it down until it touches the subfloor to measure the thickness of the floor covering and any underlayments.

FAQ

  • Plywood is a stronger subfloor material and performs better than OSB if it gets wet. OSB tends to swell up if it gets flooded, and it does not return to its original dimensions after it has dried out. However, from a cost perspective, OSB is better than plywood since it’s about half the cost of plywood.

  • Underlayment is not a substitute for subfloor. Subfloor is a thick, stable base for the floor covering (like carpeting), and the subfloor rests on top of the joists. Underlayment, if required, is a thin buffer that rests on top of the subfloor. Underlayment is never installed directly on the flooring joists.

  • OSB subfloor is the most budget-friendly subfloor material. One sheet of 23/32-inch OSB subfloor costs about $20 per 4-foot by 8-foot panel. A comparably sized sheet of plywood subfloor panel costs $40. So, plywood costs twice as much as OSB subfloor.

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