Sound Transmission Class (STC) Ratings
Thermal Insulation & Acoustics · 7 specs
Direct Answer
Sound Transmission Class (STC) is an integer rating standardized under ASTM E90 and ASTM E413 that quantifies airborne sound attenuation across interior wall, floor, and ceiling assemblies, ranging from STC 30 (normal conversation heard easily) to STC 50+ (IBC building code privacy standard for multi-family dwellings).
Source: ASTM E90 Standard Test Method for Laboratory Measurement of Airborne Sound Transmission / ASTM E413 · Last reviewed Aug 28, 2026
Specs
| Governing Standards | ASTM E90 / ASTM E413 / ISO 717-1 (Weighted Sound Reduction Index Rw) / IBC Section 1206 |
| STC 30 (Poor / Single Pane) | Normal conversation heard clearly through wall and easily understood |
| STC 35 (Basic Interior Partition) | Standard 2×4 wall with 1/2" drywall on each side (no insulation) | Loud speech heard and understood |
| STC 40 (Moderate Commercial) | Standard 2×4 wall + R-13 fiberglass batt insulation | Loud speech heard as muffled murmur |
| STC 45 (Good Privacy) | 2×4 wall + batts + double layer 5/8" drywall on one side | Loud speech barely audible |
| STC 50 (IBC Building Code Minimum) | Multi-family party wall minimum under IBC 1206 (Staggered studs or Resilient Channel RC-1 + batts) |
| STC 55–60 (High-Performance Acoustic) | Double-stud wall (separated 1" air gap) + acoustic batts + Green Glue damping compound | Music bass highly attenuated |
Standard Architectural Wall Assembly STC Rating Matrix
| STC Rating | Acoustic Performance & Privacy Level | Representative Wall Assembly Construction |
|---|---|---|
| STC 30–34 | Loud speech heard and understood clearly | Hollow core interior door or single 2×4 stud wall + 1/2" drywall each side (no insulation) |
| STC 38–42 | Loud speech audible as faint muffled murmur | Single 2×4 wood studs + R-13 fiberglass/rockwool batt + 1/2" drywall each side |
| STC 45–48 | Loud speech barely audible; normal speech inaudible | Single 2×4 studs + batts + 5/8" Type X drywall on one side + double 5/8" on other |
| STC 50–52 | IBC Multi-Family Code Minimum for Party Walls | Single 2×4 studs + batts + Resilient Channel (RC Deluxe) + 5/8" drywall each side |
| STC 55–58 | Very quiet; loud stereo music muffled | Staggered 2×4 studs on 2×6 plate + mineral wool batts + double 5/8" drywall each side |
| STC 60–65 | True Soundproof Studio / Cinema Standard | Double 2×4 stud walls (separated by 1" air gap) + 2 layers batts + Green Glue viscoelastic damping |
The 4 Pillars of Acoustic Isolation: Mass, Decoupling, Absorption, Damping
- Mass: Heavy drywall (5/8" Type X weighs 2.2 lbs/sq ft) blocks high frequencies.
- Decoupling (Most Critical): Sound vibrates through rigid wood studs. Using Resilient Sound Isolation Clips (RSIC) or Double Studs physically disconnects the two drywall leaves, boosting STC by 10 to 15 points.
- Absorption: Mineral wool batts in the cavity absorb cavity resonance.
- Damping: Constrained-layer viscoelastic polymer compounds (Green Glue) convert vibrational kinetic energy into harmless friction heat.