STC Ratings Explained

A Practical Guide for Acoustic Performance in Commercial Interiors

Acoustic performance is a critical component of modern commercial design. Whether in corporate offices, healthcare environments, or institutional spaces, controlling sound transfer directly impacts privacy, comfort, and overall user experience.

One of the most commonly referenced metrics in this process is the Sound Transmission Class (STC) rating. While frequently specified in drawings and schedules, understanding how STC ratings translate into real-world performance is essential for architects, designers, and project teams.

What Is an STC Rating?

STC (Sound Transmission Class) is a numerical rating that measures how effectively a building assembly—such as a wall, partition, or glazing system—reduces airborne sound transmission.

The higher the STC rating, the greater the sound isolation.

Typical benchmarks include:

• STC 30–35: Normal speech is easily understood through the partition
• STC 40–45: Loud speech is audible but not clearly intelligible
• STC 50+: Speech is largely inaudible, offering strong acoustic privacy

STC ratings are determined through laboratory testing under controlled conditions, providing a standardized way to compare different assemblies.

Why STC Matters in Design

For architects, specifying the appropriate STC rating is about more than compliance—it’s about delivering environments that function as intended.

In workplace settings, acoustic control supports:

• Confidential conversations in offices and meeting rooms
• Reduced distractions in open-plan environments
• Improved occupant comfort and productivity

In healthcare and institutional environments, higher STC ratings are often required to meet privacy standards and regulatory expectations.

Early consideration of acoustic performance helps avoid costly redesigns and ensures that the final built environment aligns with user needs.

Key Factors That Impact STC Performance

While STC ratings are often associated with wall types, real-world performance depends on the entire assembly and how it is installed.

Wall Construction

Stud size, spacing, insulation, and the number of gypsum layers all influence acoustic performance. Double-stud or staggered-stud assemblies can significantly improve STC ratings.

Glazing Systems

Glass partitions typically have lower STC ratings than solid walls, but advanced systems—such as double-glazed units with acoustic interlayers—can enhance performance while maintaining transparency.

Seals and Perimeter Conditions

Even high-performing partitions can fail acoustically if gaps exist at the perimeter, ceiling, or floor connections. Proper sealing is critical to achieving specified ratings.

Doors and Hardware

Openings are often the weakest point in an acoustic assembly. Door type, gasketing, and thresholds must be coordinated with the surrounding wall system.

STC vs. Real-World Performance

It’s important to note that STC ratings are based on laboratory conditions. Field performance can vary due to installation quality, adjacent construction, and site conditions.

This is where coordination between design and construction teams becomes essential.

At A&F Building Group, we work closely with architects and general contractors to ensure that specified systems are installed correctly, with attention to detailing, sequencing, and integration with other trades. This helps bridge the gap between design intent and actual acoustic performance on site.

Integrating Acoustic Performance with Flexible Interiors

As commercial interiors evolve toward modular office systems, demountable walls, and glazing solutions, maintaining acoustic performance becomes more complex—and more important.

Modern demountable and modular systems are engineered to meet targeted STC ratings while allowing for reconfiguration over time. When properly specified and installed, these systems can deliver both flexibility and performance without compromise.

Designing with Confidence

Understanding STC ratings allows architects to make informed decisions that balance acoustics, aesthetics, and flexibility.

By considering acoustic performance early in the design process—and working with experienced installation partners—project teams can deliver spaces that support privacy, functionality, and long-term adaptability.

At A&F Building Group, we support architects with detailed coordination, system knowledge, and precise installation to help ensure that acoustic design intent is fully realized in the built environment.

To learn more about our interior system capabilities, visit our Services page or explore recent projects on our Projects page.