To meet consumer demands for peace and quiet contractors and architects became tasked with finding ways to accomplish the goal of peaceful living. This was followed by building codes which decided how quiet was considered peaceful and unobtrusive. Over the years, a plethora of products and innovations have been developed to control noise on the floor above. All of these materials or methods are only one component of a complete system in which each piece plays an essential part of a total assembly. Elimination of any component in the assembly can seriously weaken the sound rating desired. It is not the floor system in and of itself that is the sole contributor to sound attenuation (reduction), every part of construction must be considered.
Most of the sound reduction data available in the market relates to tests of floor/ceiling systems that comprised of concrete slabs with gypsum wallboard hung on resilient furring channels (suspended or sound-rated ceiling system) with a layer of mineral wool or fiberglass insulation in the cavity. Unfortunately, most of the construction in the field does not have this type of ceiling treatment. Thus, rule number one should be to understand the structure you’re dealing with and how its attributes (total components) will affect the final and expected result.
It’s important to understand sound attenuation terminology and how it is used in discussing the system. The term STC (Sound Transmission Class) refers to the single figure of evaluation used to quantify the transmission of airborne sound through building elements, such as walls or floor systems. These types of sounds would be the equivalent of voices, radio, or television in the context of a multi-unit building. The term IIC (Impact Insulation Class) refers to statistical measurement standards used to quantify the transmission of impact sound energy through a floor/ceiling assembly system. These types of sounds would be the equivalent of foot traffic, dropped articles, or furniture moving in the context of a multi-family building. While enforcement is haphazard, multi-family construction in many jurisdictions must meet minimum IIC and STC values in floor and ceiling assemblies to meet local building code standards. Most common code used is published by the ICC (International Code Council) which calls for a minimum reduction value of 50 IIC and 50 STC. The higher the IIC or STC, the better the sound attenuation. You should always consult your local Building Department for the exact code requirements applicable for your area.
In addition to the building code standards, some condominium developers and homeowners associations set their own minimum standards written into their Covenants, Conditions, and Restrictions (CC&R). These are often more stringent than the building code requirements in that given jurisdiction. It is wise to consult your condo association on the CC&R standards required for IIC and STC values before installing hard surface flooring materials in your unit or project. The overall message here is if you don’t know what the requirements are, find out and avoid replacement and/or litigation later.
Impact Insulation Class (IIC) refers to a positive rating number that is used to compare and evaluate the performance of floor and ceiling construction in isolating impact noise. The IIC rating is used for specifying minimum sound control performance of assemblies in construction. Higher numbers refer to more effectiveness. ΔIIC and/or IIC are measured using either ASTM E2179 “Standard Test Method for Laboratory Measurement of the Effectiveness of Floor Coverings in Reducing Impact Sound Transmission Through Concrete Floors” or ASTM E492 “Standard Test Method of Laboratory Measurement of Impact Sound Transmission Through Floor-Ceiling Assemblies Using the Tapping Machine.” These test methods measure impact sounds on a floor surface through the use of sophisticated monitoring equipment.
Delta IIC (ΔIIC) refers to the actual IIC Value added to the floor/ceiling assembly for a particular flooring product installed on top of the actual floor construction. This value shows how much better a flooring assembly will perform, in terms of IIC, when using that particular sound control component. For example, a tile installation system incorporating a sound and crack isolation mat may add a ΔIIC of 20 to a typical 6”-thick (150mm) concrete floor, that otherwise carries an IIC rating of approximately 28 means that the total rating for this particular floor would be 48 IIC.
Field IIC (FIIC) is a positive rating number used to evaluate the performance of a floor construction and the associated structure derived from field impact sound measurements in accordance with ASTM E1007 “Standard Test Method for Field Measurement of Tapping Machine Impact Sound Transmission Through Floor-Ceiling Assemblies and Associated Support Structures.” It’s important to note that building codes allow for a difference (generally a lower rating in the field) of five points between laboratory (IIC) and field (FIIC) testing results.
Sound Transmission Class (STC) refers to a positive rating number that is used to measure the effectiveness of sound isolation in regards to audible, air-borne sound. STC is measured using ASTM E90 “Standard Test Method for Laboratory Measurement of Airborne Sound Transmission Loss of Building Partitions and Elements.” This test measures air-borne sound (e.g. voices, TV, stereos, etc…). In most cases, sound control underlayments in general, have extremely marginal or no affect on STC. The predominant factor for STC reduction is the mass of the structure, in other words, the greater the structural mass, the greater the STC performance. STC values are in large part influenced by the solid mass of the structure, but are also dependent on isolation and resilience within the structure that can be provided by the appropriate products.
Some sound reduction can easily achieve in almost any structure. However it requires very diligent adherence to the specific product manufacturer’s recommendations. As mentioned, when STC and IIC values are provided by a manufacturer they typically come as a result of a very specific assembly. When using any tile or stone product it would not be wise to install a compressive material under ceramic tile unless the product has been performance tested under ASTM C-627, the Robinson Floor Test. You should also inquire about the tile size, setting material, and grout recommendations. All may vary with each different sound reduction product. My thanks to Laticrete International for assistance in verification of several parts in this article.