Both fire and sound transmission class performance are equally critical and needed over the life span of a structure. Subsequently, we cannot choose one over the other. We need both to provide a safe environment and to meet building code(s).

Admittedly, we hope there is never a structure fire. However, if 5, 10, or 15 years from now there is, the products used must provide compartmentation, allowing safe egress, safeguarding the structure, allowing first responders to enter safely, and minimizing loss of property.

Sound transmission class performance is required daily to support privacy in medical facilities, within multi-family homes, hotels, and other similar structures. STC performance is based on the complete wall assembly. The STC rating of both the wall and floor assembly is critical. Products used to seal gaps and building joints between assemblies can only perform to the level of the complete wall assembly. In other words, a single joint fill material used to seal building joints that obtained an STC 57 used in a wall assembly providing STC 50 can only perform to the level of the complete wall assembly. A single joint fill material product cannot elevate the wall’s STC performance above its design performance level.

Assembly Requirements

International Building Code Section 1207 requires assemblies separating dwellings and/or dwellings from public or service areas, to have a STC of not less than 50 (45 if field verified). ASTM E90 (laboratory) and ASTM E336 (field) being the standards for determining STC performance.

To provide consistent, dependable STC performance over the life of the structure, the installed materials must remain pliable, adhere to the substrate, and support the structure’s design movement. Traditional products such as sealant or spray often struggle with providing these attributes over time and sealants tend to harden and separate, which can also diminish the STC performance. The performance obtained during an initial third-party sound test or initial construction can decline or no longer be achieved if the joint fill material hardens, shrinks, or pulls away from the drywall or the adjoining structure.

Fortunately, today, we have pre-formed fire and acoustic products that can withstand common weak points and deliver consistent and dependable STC performance over the life of the structure. In addition, pre-formed products can limit the liability associated with poor workmanship or declining STC performance over time.

In your next project, to minimize liability and to deliver the required performance over the life cycle of the structure, ensure:

1. Wall/floor assemblies meet the STC and fire rating requirements.
2. Joints between assemblies deliver the movement required.
3. Products installed are permanently flexible and remain adhered to the substrate.

Delivering these three items from design to construction are steps toward delivering a code-compliant structure to the owner and a safe and comfortable structure for occupants.