Understanding STC Ratings in SCIFs: Why Acoustic Security Matters 

When planning a Sensitive Compartmented Information Facility (SCIF), all areas of security matter including, access controls, alarms, perimeter protection, and one often-overlooked requirement: acoustic protection. 

This is where Sound Transmission Class (STC) ratings come into play. 

An STC rating measures how effectively a wall, door, ceiling, or any other part of the facility reduces sound transmission between spaces. In a SCIF environment, controlling sound and reducing noise is essential to help protect sensitive conversations from being overheard outside the secure perimeter. 

For project managers, understanding STC ratings, sound transmission, and acoustic performance is an important part of designing and constructing a secure facility. At CenCore, acoustic considerations are incorporated throughout SCIF construction projects to help customers identify vulnerabilities early, helping avoid costly rework and support accreditation readiness.  

What Is an STC Rating? 

A Sound Transmission Class (STC) rating is a standardized measurement used to evaluate how well a building assembly blocks sound. 

The STC rating system provides a consistent way to compare walls, doors, ceilings, and partitions. Testing standards such as ASTM E90 and rating methodologies such as ASTM E413 are commonly used to determine a Sound Transmission Class rating.  

To simplify how the rating system works: 

• Lower STC ratings allow more sound transmission 

• Higher STC ratings provide greater sound insulation 

• A higher STC rating makes conversations more difficult to hear and understand through a wall 

STC Rating Chart 

STC Rating	Typical Performance
30	Normal speech can be heard and understood
45	Loud speech can be heard but is difficult to understand
50	Loud speech is barely audible
60+	Excellent sound insulation and privacy

This STC rating chart provides a general reference, although real-world performance can vary based on wall design, installation quality, frequency ranges, and surrounding building conditions. 

When explaining STC, it’s important to remember that the goal isn’t complete soundproofing. Instead, a higher STC rating indicates greater sound reduction and less sound transmission through a wall assembly. At lower ratings, normal speech can often be understood through a wall, while at higher ratings even loud speech becomes difficult to hear.  

Why STC Ratings Matter in a SCIF 

In traditional commercial buildings, acoustic design is often focused on comfort and reducing noise. In a SCIF, acoustic performance serves a different purpose. 

Sensitive conversations occur inside secure spaces every day. Even when perimeter walls meet physical security requirements, poor acoustic performance can create vulnerabilities if conversations can be heard outside the facility. 

This is why STC ratings, sound transmission, and overall acoustic performance are important considerations during SCIF design and construction. While acoustic requirements are influenced by ICD standards and accreditation expectations, the primary objective remains to protect sensitive information and reduce the potential for unintended disclosure.  

Strong acoustic performance helps: 

• Reduce sound transmission through perimeter walls 

• Improve speech privacy 

• Reduce unwanted noise transmission 

• Support secure operations 

• Minimize costly remediation after construction 

For many SCIF projects, teams establish target STC ratings early in the design phase to guide wall construction, door assemblies, and overall acoustic planning. At CenCore, acoustic considerations are reviewed throughout the project lifecycle to help ensure secure spaces perform as intended. 

 

STC Ratings for Walls 

Throughout the construction process, one important piece to consider is STC ratings for walls. 

The performance of STC rated wall assemblies depends on several factors. Some of these factors that influence acoustic performance include: 

• Drywall quantity and thickness 

• Metal or wood stud configuration 

• Wall cavity insulation 

• Acoustic insulation placement 

• Resilient channel systems 

• Door assemblies 

• Penetrations and utility pathways 

• Installation quality 

Each wall component contributes to the overall STC value and acoustic performance of the assembly. A high-performing wall can still experience excessive sound transmission if doors, penetrations, ceilings, or adjacent building systems are overlooked. 

The result is that two walls with similar published ratings can perform very differently once installed in the field. That is why construction quality is just as important as material selection.  

Common Causes of STC Rating Failures 

Common causes of excessive sound transmission include: 

Poorly Sealed Penetrations 

Conduits, cables, pipes, and utility openings can create direct pathways for sound if not properly sealed. 

Door Assemblies 

Doors are frequently the weakest point of an acoustic perimeter. Improper installation, worn seals, or incorrect hardware can significantly reduce acoustic performance. 

HVAC Systems 

Mechanical systems can contribute to both noise transmission and acoustic vulnerabilities if sound mitigation measures are not incorporated into the design. 

Construction Deficiencies 

Small gaps, missing sealants, incomplete insulation, or undocumented field modifications can reduce a wall’s sound reduction capabilities and impact overall performance. 

These acoustic issues can stem from workmanship and installation practices rather than the specified STC rating itself.  

Why Construction Quality Matters 

These facilities may achieve an excellent STC rating in laboratory testing, but real-world performance depends on how the system is installed. 

This is where Field STC becomes important. 

A wall may perform exceptionally well under controlled factory conditions yet produce lower-than-expected results once installed. Construction quality, penetrations, doors, and adjacent building systems all influence acoustic performance. 

During construction issues like gaps, improperly sealed joints, mechanical pathways, and utility penetrations can reduce an assembly’s transmission loss and increase sound transmission. 

Testing methods such as ASTM E336 are often used to evaluate in-place acoustic performance rather than relying solely on laboratory ratings. 

For SCIF projects, achieving the desired acoustic outcome is not simply about selecting a wall with a higher STC rating. It requires consistent quality assurance throughout construction. CenCore’s Construction Surveillance Technicians (CST) helps customers identify potential acoustic vulnerabilities early, reducing project risk and minimizing costly corrections later in the process.  

How CenCore Supports Acoustic Performance in SCIF Construction 

Throughout the construction process meeting acoustic requirements involves more than selecting pieces of the assembly with the appropriate Sound Transmission Class rating. 

Successful projects require coordination between security requirements, construction activities, quality assurance processes, and accreditation planning. 

CenCore supports customers through: 

• SCIF design and construction support 

• Construction oversight 

• Security-focused inspections 

• Acoustic performance reviews 

• Quality assurance activities 

• Accreditation preparation and support 

By incorporating acoustic considerations throughout planning and construction, project teams can reduce any possible risk while improving acoustic performance and help ensure facilities meet their intended security objectives. 

Conclusion 

Understanding Sound Transmission Class (STC Ratings) and sound transmission is an important part of successful SCIF construction. 

STC ratings help ensure privacy and noise control helping support the protection of sensitive conversations within secure environments. All of the components of a SCIF build such as drywall, stud configurations, penetrations, and HVAC systems, contributes to overall acoustic performance. 

Organizations that address acoustic requirements early in a project are often better positioned to reduce risk and improve accreditation readiness. 

CenCore helps customers incorporate acoustic considerations throughout SCIF planning, construction, and accreditation support to help create secure facilities that perform as intended. 

Learn more about our SCIFs here.

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