Technical Feature: Choosing the Correct Acoustical Underlayment
Over the past 10 years, multi-family construction has increased demand for hard surface flooring, whether this be tile, stone, engineered wood, or vinyl plank. Unfortunately, these hard floor coverings accentuate sound vibrations, which lead to complaints from residents. When sound enters high-rise concrete structures, it travels through the concrete as vibration and radiates into multiple units, disturbing occupants. Installing a high-performance acoustical underlayment underneath the finished floor prevents these vibrations from entering the structure. This interstitial layer between the finished floor and concrete structure decouples the contact points, limiting excess impact noise or any other vibrations caused by the structure.
The International Building Code (IBC) has mandated multi-family construction to meet certain levels of sound attenuation in two classes, sound transmission class (STC) and impact insulation class (IIC). These classes take care of airborne (STC) and impact (IIC) noise. Airborne noise includes loud music, yelling, singing, etc. Impact noise can be caused by activities like high heels, moving furniture, or dancing. Ratings are given to a floor-ceiling assembly when it has been tested in a third-party NVLAP accredited laboratory. Ratings mandated for minimum levels of sound control are STC/IIC 50 when tested in a laboratory and STC/IIC 45 when tested in the field. If these levels are not met, developers, architects, and contractors may be liable for the repairs needed to meet IBC and local building code requirements.
Some manufacturers take advantage of these simplified standards by providing a test report that is high performing but not representative of real-world conditions. Many developers, architects, and contractors believe if there is a test report with a rating above minimum code, the products included will be acceptable for that building. This is not always the case, since laboratory and field tests can be manipulated to show false ratings of products presented.
Understanding how tests are performed is the best way to distinguish between materials that are qualified to meet the IBC requirements and those that are not. The most important detail to understand is that one acoustical underlayment does not achieve an IIC rating on its own. The entire floor-ceiling assembly, including the finished floor, acoustical underlayment, subfloor structure, and ceiling details, is required to achieve these ratings.
One of the biggest discrepancies when testing an assembly is an IIC rating of a bare concrete slab compared to one with a drop ceiling. An 8” bare concrete slab on its own will not meet IIC 50, but with a 10” drop ceiling full of insulation, it will reach IIC levels into high 50s or low 60s. Manufacturers may use drop ceilings to help boost their underlayment and show higher results. Issues arise when the floor-ceiling assembly of a design calls for a bare slab and the specified product was tested with a drop ceiling.
When choosing an acoustical underlayment for tile and stone, two major properties should be met: acoustics and crack isolation. Acoustics can be verified through a third-party laboratory test or a field test conducted by an acoustical consultant using ASTM E492, E90, and E1007 standardized test methods. Crack isolation can be verified using ASTM C627 Robinson Wheel Testing to meet minimum residential ratings. Companies that provide a significant amount of testing on both fronts insure results to architects and developers. Specifying products from these companies leads to confidence in a finalized product and overall fewer complaints from building occupants.
Ryne Sternberg is a chemical engineering graduate of Penn State University, and business development engineer with Pliteq Inc. – an engineering firm dedicated to providing products that will satisfy acoustical standards, crack isolation of tile and stone as well as any other requirements placed on floor-ceiling assemblies of design. All products are derived from recycled rubber content, which achieve the best vibration and acoustic results and contribute to LEED. These products are backed up with over 700 completed laboratory and field test reports. For more information, visit www.Pliteq.com.