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What Is STC Rating? A Contractor's Guide to Sound Transmission Class

Posted by Core Insulation Supply on May 28th 2026

Demystifying Sound Transmission Class (STC)

If you are a contractor building a home theater, recording studio, or multifamily complex, you must understand STC ratings. Sound Transmission Class (STC) is an integer rating of how well a building partition attenuates airborne sound.

STC Rating wall assembly diagram

How to Achieve a High STC Rating

A standard interior wall (drywall on wood studs) has an STC of around 33—meaning loud speech can be heard clearly. To push that STC rating above 50 (where loud speech is barely audible), you need three things:

  1. Mass: Double layers of 5/8" drywall.
  2. Absorption: Filling the cavity with dense acoustic insulation like ROCKWOOL Safe'n'Sound® or ROCKWOOL AFB®.
  3. Decoupling: Breaking the structural vibration path using Resilmount® Sound Isolation Clips and furring channels.

By combining ROCKWOOL and Resilmount systems, contractors can easily achieve STC ratings of 60+, meeting strict building codes and exceeding client expectations.

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