Strategies To Improve STC Ratings

Aug 30, 2023 by Amy Wilson

OnBoard Newsletter | August 2023

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What is an STC rating?

Sound is energy transmitted by vibration through a medium. When sound travels from one room to another, it can be measured with a Sound Transmission Class (STC) rating. The STC rating is tested in accordance with ASTM E90: “Standard Test Method for Laboratory Measurement of Airborne Sound Transmission Loss of Building Partitions and Elements” and scores how well a wall assembly mitigates airborne noise between spaces.

Higher STC ratings indicate the assembly is more effective at reducing sound transmission. With this knowledge, you can design your assembly to achieve the desired level of sound control. The International Building Code designates 50 as the minimum allowable STC rating between units in a multifamily building.

Continue reading to discover the valuable strategies that can assist you in meeting the necessary STC requirements for your project.

Six variables to consider for optimal STC ratings

1. Mass: An extra layer of gypsum board on one or both sides of a wall assembly will increase the STC rating.

2. Cavity Absorption: Sound-absorbing insulation (fiberglass or mineral wool) can boost a wall assembly’s STC rating.

3. Cavity Depth: A deeper partition cavity can increase the amount of sound transmission loss, especially if filled with acoustical insulation.

4. Stiffness: The thickness of a stud affects the STC rating. Choose metal, thinner-gauge studs and alter stud spacing from 16” o.c. to 24” o.c. to positively impact an STC rating.

5. Decoupling: Construct chase walls, stagger the studs, add resilient channels or add Resilient Sound Isolation Clips to decouple one side of the partition from the other. These strategies can increase an STC rating by 5 to 14 points.

6. Damping: Gold Bond® SoundBreak XP Wall® Board has an embedded layer of viscoelastic polymer between two layers of gypsum board, which effectively provides sound damping. One additional layer of SoundBreak XP Wall Board can increase the STC rating up to 11 points.

Wall assemblies with the same STC rating are not always equal in performance. The sound transmission loss at each frequency can vary, highlighting the importance of reviewing the assembly sound test. Check out a recent post from the NGC Blog for in-depth information about the six STC design considerations and how to create better acoustical wall assemblies.

OITC Infographic
Click to view infographic

The Outdoor-Indoor Transmission Class (OITC) is a more recent rating system that measures the transmission of street noises such as car horns, sirens and construction noises through exterior walls, windows, doors and other building assemblies. Similar to the STC rating, a higher OITC rating indicates outside noise will be less detectable. The OITC rating system emphasizes low-frequency sounds in its calculations. It provides additional valuable information when addressing noise issues caused by outdoor sources.

 Please feel free to reach out to your construction design manager if you have additional questions about acoustics.

"The SoundBook is an excellent guide to utilize when researching options for your projects’ noise-control requirements. This resource is organized by framing material, size, gauge and number and type of gypsum board layers to make assembly selection easy. Illustrations in the guide allow you to quickly evaluate and compare different acoustical assemblies."

Amy Wilson


Amy Wilson

Construction Design ManagerNational Gypsum Company

"Specifying partitions that meet the acoustical requirements of your projects can be difficult. Your construction design manager is here to help. We offer specific project guidance as well as an AIA Lunch N Learn that covers the topics discussed in this issue of OnBoard. Please do not hesitate to contact us."

Scott Hughes


Scott Hughes

Construction Design ManagerNational Gypsum Company

Acoustical Resources

FAQs - Answers to commonly asked questions about acoustical assemblies and STC ratings. Explore now!

The SoundBook® - With more than 300 tested acoustical assemblies, The SoundBook provides solutions for your toughest acoustical challenges. Download now!

Building Knowledge Together® - Reach out to your construction design manager and book your upcoming continuing education session: Acoustically Enhanced Gypsum Board Designed for High STC Wall Partitions.

Product Spotlight | SoundBreak XP Family of Products

Need innovative noise-reduction solutions between interior units, floors and ceilings or enhanced acoustical performance of an existing wall assembly? Count on the SoundBreak® XP® family of products to get the job done. Watch our video to see how these products help prevent noise pollution between spaces.


Project Profile | Charlotte Rescue Mission

Owner: Charlotte Rescue Mission | Charlotte, NC

Developer: JLL | Charlotte, NC

Architect: LS3P Associates Ltd. | Charlotte, NC

General Contractor: Rodgers Leeper | Charlotte, NC

Drywall Contractor: Spectrum Interiors | Charlotte, NC

Charlotte Rescue Mission’s new 72,000-square-foot Rebound Center facility will provide shelter and addiction recovery services for Charlotte area men. Scheduled to open in spring 2024, the modern building will nearly double its capacity, helping some 500 participants each year find a transformative future of hope and wholeness.

Read more about this project and the products used.

Rendering courtesy of LS3P Associated Ltd.

Learning Opportunities

NGC Blog - Discover a wealth of information on the NGC Blog, where we share insightful articles on a wide range of topics. From designing fire and sound wall assemblies to exploring the impact of high-performance building products, take your expertise to the next level by delving into the NGC Blog today.

Continuing Education - Expand your knowledge and skills with our wide array of in-person and online continuing education courses, all of which are eligible for AIA learning credit. Contact your construction design manager today to schedule your next course.

Expert Connection

From expertise on building products in fire- and sound-rated assemblies to specifying the best products for your next project, we have a construction design manager available to provide architectural design assistance every step of the way. We are here to help you design and build better. Connect now!

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