Mass timber construction has rapidly transformed modern building design—offering sustainability, faster construction timelines, and a warm, natural aesthetic that resonates with today’s apartment and office environments. But with exposed wood ceilings as a defining feature, acoustical performance becomes one of the most critical—and often overlooked—design challenges.
Why Acoustics Matter in Mass Timber
Unlike traditional assemblies that rely on drop ceilings or heavy concrete slabs, mass timber structures often leave the underside of the floor exposed. While visually striking, this creates a direct path for sound transmission.
Bare mass timber panels alone typically underperform acoustically. For example, a cross-laminated timber (CLT) floor can have an STC of ~41 and IIC of ~25, far below acceptable building standards. Most building codes and occupant expectations require ratings of 50 or higher.
This means acoustical design isn’t optional—it must be engineered into the floor assembly.
Understanding IIC vs. STC in Floor Design
To properly design for acoustics, it’s essential to address two different types of sound:
- Impact Insulation Class (IIC): Measures how well a floor reduces structure-borne noise like footsteps, dropped objects, and furniture movement
- Sound Transmission Class (STC): Measures how well a floor/ceiling assembly blocks airborne sound such as voices, TVs, and music
A successful mass timber assembly must address both simultaneously.
Floor Assembly Strategy for Mass Timber
1. Sound Control Mats for Impact Noise (IIC)
One of the most effective ways to improve IIC ratings on mass timber construction is through the use of high-performance sound mats.
Keene Building Products Quiet Qurl® sound mats are engineered specifically for this purpose:
- Provide resilient separation between the structural deck and finished floor
- Absorb and dissipate impact energy before it travels through the structure
- Improve IIC ratings significantly without adding excessive height or weight
Because mass timber structures lack inherent damping, adding a resilient layer like Quiet Qurl is essential to prevent impact noise from transferring directly through exposed ceilings. For a more efficient sound mat, Quiet Qurl® 013 MT was engineered to deliver high acoustical performance with less material and less thickness. Quiet Qurl 013 MT allows for a 7/8″ floor assembly—up to 3/8″ thinner than typical sound mat systems—while maintaining the STC, IIC, and HIIC ratings required for modern multifamily construction.
2. Perimeter Isolation: Preventing Flanking Noise
Even with a high-performing sound mat, sound can “flank” around the assembly—traveling through walls and structural connections.
This is especially problematic in mass timber, where continuous panels can carry vibration across units.
Quiet Qurl Perimeter isolation addresses this by:
- Decoupling the floor from surrounding walls
- Preventing rigid connections that transmit vibration
- Maintaining the integrity of the acoustical system
Without perimeter isolation, even the best floor mat can be compromised.
3. Gypsum Underlayment for Airborne Noise (STC)
To control airborne sound, additional mass and separation are required.
Keene Building Products GSL (gypsum-based underlayment systems) enhance STC by:
- Adding mass to the floor assembly
- Reducing airborne sound transmission between units
- Creating a more balanced acoustical system when combined with sound mats
This layered approach—mass + isolation—is critical for achieving target STC ratings in exposed mass timber designs.
Putting It All Together: A System Approach
Designing acoustics in mass timber isn’t about a single product—it’s about a complete system:
Recommended Assembly Strategy:
- Mass timber structural deck (CLT or similar)
- Quiet Qurl® sound mat (impact isolation)
- GSL underlayment (airborne sound control)
- Perimeter isolation (flanking prevention)
This integrated approach ensures:
- Higher IIC ratings (reduced impact noise)
- Higher STC ratings (reduced airborne noise)
- Fewer post-occupancy complaints
- Preservation of exposed timber aesthetics
Project Spotlight: How Quiet Qurl Reduced Impact and Airborne Noise for Intro Cleveland Apartments
Intro Cleveland stands as one of the largest mass timber developments in the United States – a nine-story mixed-use structure located in the heart of Ohio City. To preserve the exposed timber ceilings architects desired, while meeting IBC sound transmission requirements, the project team turned to Keene Building Products’ QuietQurl® system to form the acoustic layer between the timber structure and the finished floor.
Final Thoughts
Mass timber construction delivers unmatched sustainability and design appeal—but it demands a smarter approach to acoustics. Without proper planning, exposed ceilings can quickly lead to noise complaints, callbacks, and compromised occupant comfort.
By combining sound mats, perimeter isolation, mass-enhancing underlayments, and structural decoupling systems, designers can achieve high-performance acoustical assemblies—without sacrificing the beauty that makes mass timber so compelling.
In today’s multifamily and commercial environments, acoustical performance isn’t just a technical requirement—it’s a competitive advantage.
