Hardwood Floors February/March 2026

AT THE SITE Resiliency in Acoustical Underlayments (Continued)

Once an acoustical underlayment compresses and loses height, its acoustical performance drops significantly, and the floor may feel harder and noisier. Think of it this way: a good acoustical underlayment acts like a shock absorber. It cushions impact, reduces sound transmission, and maintains its structure under pressure. Without these qualities, the flooring system can fail to deliver the comfort and quiet consumers expect. ACOUSTIC BASICS A Flooring underlayments are tested as part of a system to simulate a typical floor/ceiling assembly. The floor, underlayment, adhesive, substrate, and the ceiling assembly are combined to evaluate performance against IIC, Delta IIC, HIIC, and STC ratings. These values show how the assembly performs in various noise tests, from footsteps to airborne sound. u Manufacturers often test multiple assemblies to provide a broader understanding of their product’s capabilities. Generally, denser acoustical underlayments, like synthetic rubber, tend to resist deflection better than some other types. It is not uncommon to find these types of underlayments used in applications requiring vibration control. INSTALLATION CONSIDERATIONS I

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Beyond material properties, consider installation methods and substrate compatibility. The underlayment should work over concrete slabs, wood subfloors, and floors treated with leveling compounds. Ideally, it should be suitable for glue-down or floating installations. s t

As with any flooring project, success starts with proper substrate testing. Check for moisture and flatness, as prep work may be needed. Underlayments cannot correct substrate problems; they will conform to irregularities, which can telegraph through the flooring or create voids under wood floors. A little extra time spent on prep can prevent costly callbacks later.

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Acoustical underlayment materials may include cork, synthetic rubber, recycled rubber or cork/ rubber blends, foam pads, recycled cellulose fiber materials, and dimpled or peel-and-stick membranes. For additional information, refer to the Underlayments: Sound Control/Acoustical section of the NWFA's Installation Guidelines on page 110 at NWFA.ORG/TECHNICAL-GUIDELINES/.

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