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Subfloor and Underlayment Recommendations

How to achieve the ideal Steller Floors installation - and what to do if you can't

In most homes and commercial spaces, Steller Floors are designed to feel and perform like traditionally nailed or glued-down hardwood—solid, quiet, and durable. That means the subfloor beneath matters.

While ideal subfloor conditions provide the fastest installation and best long-term performance, we recognize that many real-world subfloors fall short. Fortunately, functional installations are still possible in many imperfect settings—often making Steller Floors your best choice even when other floors won't work.

However, some subfloors do need remediation before any flooring (including ours) can be installed safely or successfully.

Ideal Installation Conditions

If you're aiming for optimal performance and the easiest install, your subfloor should be:

  • FLAT  - Deviations should not exceed 3/16" over a 10' radius.

  • FIRM - OSB or plywood panels should be fully supported underneath, with no noticeable deflection.

  • DRY

    • Concrete: ≤ 75% relative humidity (RH)

    • OSB/Plywood: Moisture content between 6%–12%. Anything wet from rain or construction must be dried prior to installation.

Moisture Resistance: Moisture Barrier Guidelines

Moisture can damage any hardwood flooring over time, so it's important to determine if your subfloor assembly needs a moisture barrier, or more critically, moisture remediation before you begin.

a) Moisture in Slab – Barrier Required

If you’re installing over a concrete slab—even on an upper level—moisture vapor can wick upward and damage flooring.

✔️ Solution: Use 6 mil polyethylene sheeting taped at seams. It’s cost-effective and highly effective for vapor control. Liquid-applied moisture barriers are also ok.

b) Occasional Humidity Below OSB – Barrier Recommended

If your space sits over a crawlspace or unfinished basement, occasional humidity is common.

✔️ Solution: Use red rosin paper, or housewrap. These help reduce vapor transmission and are compatible with most OSB floors.

c) Endemic Moisture or Condensation – Remediation Required

If your wooden subfloor structure is exposed to constant or condensing moisture (e.g., visible mold, damp joists, or standing water), do not install flooring or a moisture barrier yet.

⚠️ Problem: A barrier will trap moisture and accelerate structural decay.
🛠️ Remediation Required: Resolve water ingress, improve ventilation, or install a ground vapor barrier in crawlspaces before continuing with any flooring project.


Functional Installations: When Subfloors Aren’t Perfect

There are many real-life situations where the ideal subfloor isn’t practical—older homes, condos with noise ordinances, or spaces where leveling the subfloor isn’t desirable. In these cases, a fully functional Steller Floor installation is still possible, and may outperform alternative flooring options.

Typical Functional Use Cases

  • Noise-sensitive environments (HOAs, condos with acoustic requirements)

  • Ergonomic floors (gyms, dance studios, play areas)

  • Aging or imperfect subfloors where repair isn’t feasible

Installation Approaches

To simulate a standard install and minimize performance issues:

  • Option A: Simulate Ideal Conditions
    Use a stiff layer (like ½" plywood) on top of your underlayment to create a firmer surface before installing Steller Floors.

  • Option B: Reduce Symptoms
    Install directly over compliant or imperfect surfaces while managing expectations:

    • Expect some soft “give” or deflection underfoot
    • Slightly more difficult installation
    • Risk of noise or wear from imperfect flatness (especially if lippage occurs)

Additional Functional Tips:

  • For soft underlayments, choose materials with Shore A Hardness ≥ 60 durometer
  • Shim low spots after installation to reduce flex and noise

Non-Functional Conditions: When Steller Floors Won’t Work

While Steller Floors are versatile, there are situations where a successful installation isn’t possible because underlayment materials are too compliant or subfloors are too irregular. These include:

  1. Soft, fabric-backed, or foam underlayments thicker than 2mm
  2. Soft cork underlayment with durometer under 60
  3. Uneven subfloors with severe irregularities, including:
    1. Vertical discontinuities > 1/16" within 1"
    2. Gaps > 3" between panels
    3. Non-planar adjacent panels (different heights, warping)

In these cases, the result is:

  • Visible deflection or lippage
  • Difficult installation
  • Increased noise levels from floor movement
  • Chipping or damage at edges and corners

Summary: What to Expect Based on Your Subfloor

Subfloor Condition Installation Type What to Expect
Flat, firm, and dry Ideal Fast install, nailed-down feel, quiet and durable
Slight imperfections or soft underlayments Functional Some deflection, slower install, possible lippage/noise 
Major unevenness or soft sublayers Non-Functional Install not recommended – will not perform reliably

 

Considering something not listed? There seems to be a never ending list of new underlayments available! The awesome part of a Steller Floor is that if you have some extra time, you can always test a small section of flooring over the underlayment you choose and decide if it will work for you. If you decide against it, disassembling the flooring and using it again during your install is a breeze.

Also feel free to reach out to our support team at support@floorsbysteller.com, and we can look over product specs with you to see if we can anticipate issues with any potential materials.