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How Flat Does My Subfloor Need to Be?

Your subfloor needs to be flat, not perfectly level. Flat means no abrupt dips or peaks: within 3/16" over 10' for Modin LVP and Arista, 1/8" over 6' for Modin Herringbone, and 1/16" over 6' for Silvan.

Flatness vs. Levelness
  • Levelness is whether your floor is perfectly horizontal. A room that slopes gradually from one end to the other isn't level, but that's fine.
  • Flatness is what matters. A flat surface has no sudden peaks, dips, or bumps, even if the room tilts overall. A consistent slope with no abrupt irregularities won't cause problems. Unexpected rises and valleys will.
Requirements by Collection
  • Modin LVP (all lines except Herringbone): 3/16" over 10'. Test: the gap under a 10' straightedge stays at or under 3/16" at any point.
  • Modin Herringbone: 1/8" over 6' and 1/16" over 1'. Test: two stacked quarters at 6' and one quarter at 1'. Neither should slide under a straightedge.
  • Silvan: 1/16" over 6'. Test: one quarter shouldn't slide under a 6' straightedge anywhere.
  • Arista: 3/16" over 10'. Test: the same 10' straightedge check as Modin.

Check with a long straightedge in multiple directions. Mark problem areas before you start laying planks.

A Note on Modin Herringbone: The strictest tolerance we have, both at 6' and at 1'. Because planks install at an angle, small irregularities have an outsized impact on joint stress and appearance. Budget extra prep time.

 

How to Fix It

  • High spots: sand or grind down mechanically. Don't try to bridge with underlayment.
  • Low spots: fill with a Portland cement-based patching compound or self-leveling compound. Trowel smooth and cure fully before installing.
  • Existing tile grout lines (Modin only): fill recessed lines and skim-coat until flush with the tile surface.

Underlayment is not a correction tool. Fix the subfloor first, then add underlayment.

 

Full Installation Guides

For complete subfloor prep instructions, moisture requirements, existing subfloor compatibility, and underlayment guidance:

Common Questions

My room slopes. Do I need to level the whole floor?
Not if the slope is gradual and consistent. Run a straightedge across it, if the gap stays within tolerance, you're fine. Levelness isn't the issue. Abrupt changes in height are.

Can underlayment compensate for a slightly uneven subfloor?
Underlayment adds cushion and sound dampening over a subfloor that already meets spec. It won't bridge dips or fill gaps, and should never be used to level out an uneven subfloor.

Questions? Email support@flooret.com or call 1-800-700-8122. M-F, 8 AM–7 PM CST.