How to reduce sound transmission in floor-ceiling assemblies

Sep 28, 2022

Reducing sound between floors can lead to increased indoor environmental quality and happier residents and tenants


Unwanted sound, whether it’s a conversation, the beeping of a jammed printer or footsteps on a hard surface floor above, can adversely affect hospital patient well-being, office worker productivity and apartment resident comfort. By designing structures that minimize noise passing through floors and ceilings, architects can create spaces better suited for work, play and everyday living.

Learn how to effectively reduce sound between floors and which products manufactured by Gold Bond Building Products can help you achieve the level of sound reduction needed for any project.

How does sound travel?

There are two types of sound transmission through floor-ceiling assemblies, airborne sound and impact sound. Airborne sound, such as that from voices or loud music is caused by fluctuations in air pressure, causing assemblies to vibrate. Impact sounds (such as footsteps on the floor above) are caused by vibrations through the structure caused by objects striking surfaces.

The difference between wall and floor-ceiling sound reduction

When it comes to wall partitions, sound mitigation strategies target airborne sounds like speech, music and television noise. When it comes to reducing sound between floors, in addition to airborne sound, sounds created by impacts on the floor above like walking, furniture movement or dropped objects are also targets for sound control.

What is the difference between the acoustical ratings STC, NRC, CAC and IIC?

The acronyms STC, NRC, CAC and IIC can cause confusion. Here’s a top-line overview of these acoustical ratings:

  • Sound Transmission Class (STC): Rates an assembly’s ability to resist the passage of airborne sound at 16 frequencies between 125 Hz and 4,000 Hz. It is a measure of the sound reduction between spaces.
  • Noise Reduction Coefficient (NRC): Measures the absorption of airborne sound energy by the surfaces of a room and objects within the room. Soft materials absorb more sound than hard materials.
  • Ceiling Attenuation Class (CAC): Measures airborne sound transmission between adjacent spaces through a shared plenum where sound travels through the ceiling over a dividing partition and down through the ceiling in the next room.
  • Impact Insulation Class (IIC): Measures the effectiveness of a floor system at reducing impact sounds such as foot traffic
Sound Book
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How does Gold Bond SoundBreak XP Fire-Shield C reduce sound transmission through floors and ceilings?

SoundBreak® XP® Fire-Shield C™ Gypsum Board consists of two high-density gypsum panels laminated together with a sound-damping viscoelastic polymer. SoundBreak XP reduces sound transmission in two ways:

  • The high-density gypsum board has greater mass than standard gypsum board to reduce sound energy.
  • The viscoelastic polymer dissipates sound energy by transforming it into negligible heat.

What are the advantages of SoundBreak XP Fire-Shield C?

  • Provides high STC and IIC ratings when tested as part of a floor-ceiling assembly by an independent third-party acoustical laboratory using ASTM E90 test procedures.
  • Provides both STC and IIC ratings above 60 in specific floor-ceiling assemblies, making it a best-in-class solution by reducing sound two times more than the code requires.
  • Provides 1-hour fire ratings in wood-framed floor-ceiling assemblies.

Can SoundBreak XP Fire-Shield C be used with other sound reduction methods?

For even greater sound dampening between floors, install SoundBreak XP Fire-Shield C in combination with resilient channels or clip systems to mitigate sound transmission. Sound energy travels faster through denser materials such as subfloor panels and wood joists. Resilient systems interrupt the path of sound with steel channels, decoupling the gypsum board ceiling membrane from the framing.

What building types need floor-ceiling sound reduction the most?

Reducing sound between floors is paramount — nobody wants to hear their neighbors. Most buildings need some degree of sound dampening between floors. Some building types where sound control is important, include:

  • Wood-framed apartment buildings
  • Multifamily buildings
  • Commercial office buildings
  • Health care facilities
  • Hotels

With wood-framed multifamily buildings, sound dampening between floors provides a sense of privacy at home.

Special attention to sound transmission between spaces is important in commercial buildings. For example, in designing a hospital, give special attention to mitigating chair scooting noises in the cafeteria, especially if it’s sandwiched in between patient rooms.

Buildings in the hospitality sector, including hotels, spas and resorts, also call for special attention to sound dampening between floors to create an optimal experience for visitors, especially in hotels. With guests coming and going all hours of the day, decreasing the vibration and impact sounds between floors can lead to happier customers and satisfied building owners.

Download The SoundBook® to select assemblies that achieve the desired acoustical goals and requirements of your specific project.


Editor’s Note: We’ve recently updated this post to reflect a change in product name. For clarity, the revised name for SoundBreak XP Ceiling Board is Gold Bond® SoundBreak® XP® Fire-Shield C™ Gypsum Board. Contact 1-800-NATIONAL if you have additional questions.