27 Aug Designing for Quiet: What I learned from National Gypsum’s Webinar on Sound Control Assemblies
A few weeks ago, I had the opportunity to join a fantastic webinar hosted by National Gypsum exploring STC ratings and sound control assemblies, an area of building science that’s often overlooked in single-family residential projects, but critically important when it comes to designing attached ADUs (Accessory Dwelling Units).
Whether you’re an architect, builder, or homeowner considering adding rentable space to your property, understanding sound transmission and fire-rated assemblies can make or break the comfort and performance of your design.
What Is STC, and Why Does It Matter?
STC (Sound Transmission Class) measures how well a building assembly—like a wall or floor—reduces airborne sound between rooms. While typical single-family homes don’t require STC-rated assemblies between interior walls, the game changes when you’re working on attached ADUs or multifamily configurations.
In these cases, building codes generally require:
One-hour rated assemblies.
STC rating of 50 or higher.
IIC (Impact Insulation Class) rating of 50 or higher
This ensures privacy, safety, and livability—especially when one dwelling unit is intended for tenants or short-term guests.
Key Takeaways from the Webinar
The webinar offered practical strategies and a few surprising facts about improving sound performance in residential construction. A few highlights:
Metal studs outperform wood studs in sound assemblies because they’re less rigid and transfer less vibration.
24″ on-center framing is actually better for sound control than 16″ on-center, as the greater spacing reduces the number of rigid connection points for sound to travel through.
Resilient channels and decoupling finishes (like floating drywall layers) are great ways to prevent direct sound paths and increase STC values.
Using products like Gold Bond® SoundBreak® XP® can significantly enhance the acoustic performance of a wall or ceiling system without overly complicating the construction process.
The bottom line: thoughtful design and product selection matter, especially when you’re aiming for both code compliance and comfort in attached dwelling units.
Resources Worth Bookmarking
If you’re diving into ADU design, remodeling a rental unit, or simply curious about soundproofing, here are a few fantastic resources from National Gypsum that were shared during the webinar:
These are packed with pre-tested assemblies, STC/IIC ratings, and design tips tailored to both wood and metal framing.
Why This Matters for Homeowners and Architects Alike
As California and many other states continue to encourage the development of ADUs for extended family, rental income, or aging in place, the quality of these secondary units will define how successful they are. Good design goes beyond square footage—it’s about the experience of space, and sound plays a major role in that.
If you’re planning an ADU or renovation and want to learn more about integrating code-compliant acoustic and fire-rated assemblies without compromising aesthetics or budget, we’re always happy to help guide the process.
Let’s design smarter and quieter.
If you’re thinking about building an ADU or want to retrofit for better privacy and peace, feel free to reach out or explore our other blog posts for more technical tips and inspiration.
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