In the world of architecture, we frequently hear the term “mixed-use development,” and our firm is increasingly called upon to provide mixed-use development acoustical consulting. The term “mixed-use” generally refers to a development that incorporates residential and commercial space in a close-knit fashion. Mixed-use developments have been constructed for centuries, often taking the form of residential space above retail space – such as the shopkeeper living above the shop. As industrialization increased, mixed-use fell out of favor, and segregated land-use became popular. But late in the past century, mixed-use developments resurfaced, often with the intent of revitalizing urban areas and creating walk-able communities – as opposed to communities where a person must drive a car or take some form of public transportation to perform their daily routine.
So what do acoustics have to do with mixed-use developments? Well, as it happens, quite a lot. What happens when the shopkeeper moves out and a new tenant moves in? This new type of occupant will find noise from the shop to be a great nuisance and will desire a high degree of noise isolation. It’s the most common acoustical issue we face in mixed-use developments: the problem of adjacency. That is, spaces that share adjoining walls, floors, or ceilings often have differing levels of noise sensitivity: restaurants below condominium units, night clubs within an apartment building, grocery stores on the first level of a residential building. We see all sorts of combinations, and for the most part, there are no building codes in place to adequately address the noise incompatibilities.
Local building codes are usually based upon either the Uniform Building Code (UBC) or the International Building Code (IBC). Both of these codes require minimum levels of sound isolation for multi-family residential units: Sound Transmission Class 50 (STC50) and Impact Isolation Class 50 (IIC50).
STC is a measure of the amount of sound blocked by a partition. It applies to walls and floor-ceiling assemblies separating a residential unit from another residential unit or from spaces used for other purposes. So, for example, if a sandwich shop will occupy the storefront below an apartment, most building codes would require that the floor-ceiling assembly between these spaces meet a rating of at least STC50 (the higher the STC rating, the more sound is blocked). IIC, on the other hand, applies to sound generated by people walking in the space above. The IIC of a floor-ceiling assembly, therefore, would be less critical for the situation where there is an apartment over a sandwich shop. The IIC becomes critical where there is residential above residential, or as is sometimes the case for hotels, where there is a restaurant above hotel rooms. Unfortunately, these minimal building code requirements are often completely inadequate for reducing noise disturbance between spaces with dissimilar uses.
At Acoustics By Design, we regularly take phone calls from unhappy residents of mixed-use land developments. The story line is almost always the same: they signed the lease because it was a trendy apartment, or because it was located downtown, or because it was a good deal, but they did so without giving the slightest thought to the potential noise problems. After moving in, they find the noise to be disturbing their quality of life, and they want it fixed, but they have a problem: they already signed the lease!
At this point, options for the tenants or the property owner can be limited. Even if a sound study is performed, the costs for retrofitting a noise isolation solution can be steep, and the costs for going to litigation can be even more prohibitive. Often, improving the sound isolation means moving all affected tenants out of the building while walls or floor-ceiling assemblies are altered… which can be especially problematic and often impossible for commercial tenants.
As an acoustical consulting firm, the best scenario is to be involved in the process during the design phase, long before construction begins. This way, we can assist in optimizing constructions that provide sufficient levels of noise control in addition to meeting the other design requirements. Incorporating these construction features into the original design can be much more cost effective than attempting to fix problems after construction is complete; it can keep residents happy and shopkeepers busy.