Photo © Raj Das
This method would result in a thicker-looking mullion from the outside of the building as the drywall extension would often be visible. Specifically made and acoustically tested systems provide caps to close the gap between the end of the drywall partition and the façade. These systems provide a cleaner-looking, less-visible connection from the outside of the building, as well as a slip connection to allow the façade to expand as it heats up. These caps also provide tested acoustical separation from STC 35 to 60. In the author’s experience, the acoustical separation provided by the partition will be significantly limited if this connection is unaddressed. If the drywall partition stops at the mullion and the gap is filled with backer rod or a neoprene gasket, a partition with a single layer of drywall on each side (including the batt insulation) should be considered, as the mullion/partition connection will limit the acoustical separation from anything higher than this partition.
The gap between the structural floor and the façade is another weak link for the acoustics within the building. Acoustical separation at the perimeter can be compromised due to the gap between these two locations. Drywall window return enclosing the gap can help address the attenuation required between these two vertical adjacencies. However, mixed-use adjacencies may need more significant construction to provide adequate acoustical separation.
In the past, zoning used to address restaurant and bar activities by providing distance between commercial and residential uses. The mixed-use concept, allowing occupants to socialize locally rather than commute to an activity, is becoming popular. While this is beneficial to the community, it requires improved acoustical separation. As mentioned, a restaurant or bar located within a mixed-use building may operate well into the nighttime, and even if live music is restricted, will cause noise levels that would be disturbing to the residences above. In leases, landlords are adding a requirement of ‘inaudibility’ and/or acoustical separation as high as STC 75 between these adjacencies. While the structural building with poured concrete slabs may already be providing this separation, without ‘box-within-a-box’ construction at the perimeter, the gap between the structure and the façade limits the acoustical separation. To achieve higher acoustical isolation, a separate façade, attached resiliently from the building structure, and closing off the acoustical ceiling or floor is required (Figure 3).
Conclusion
As a final thought, all components of the building allow the façade to properly expand and contract. Without providing slip connections and avoiding rigid connections between the façade and interior components such as the acoustical ceiling grid, pops and creaks occur as the two components heat up differently and attempt to expand.
While the visual, thermal, and fire/life safety aspects of the façade are the most discussed factors, the acoustical considerations discussed above are also an important part of the overall success of a project. Such concerns require careful detailing and construction to provide the appropriate acoustical environment to building occupants. An integrated team with the ability to address all of the relevant design considerations is crucial to maximize the mixed-use trend, while minimizing some of the concerns associated with living close to other people and different uses.
