Anybody who has lived in an apartment and had to knock on the wall to get the neighbor to turn down their radio knows firsthand how annoying unwanted noise can be. While airborne noise—and a product’s ability to counter it—is measured through a Sound Transmission Class (STC) rating, for flooring the most important number is the Impact Insulation Class (IIC). A high IIC will help ensure floors remain quiet, so the sound of footfalls aren’t transmitted through your floor into the downstairs neighbor’s ceiling.

In this month’s roundtable, we speak with manufacturers of sound control products to find out the importance of understanding not only the IIC rating but the Delta IIC as well, learn some best practices for working with sound control membranes and adhesives, and take a look at some of the industry’s latest sound control offerings.

Panelists are: Thomas Utley, Ardex technical consultant and sound underlayments expert; Sonya Moste, MAPEI product manager for crack isolation & sound control membranes; Dean Cunningham, Laticrete technical service manager; Brian Petit, president of NAC Products; Shane Jenkins, senior technical coordinator, Schönox HPS North America; David Jackson, DriTac field technical services manager; Beth Lee, Maxxon’s senior development and project manager; Kyle Erickson, Schluter research and development engineer; and Alex MacDonald, USG’s manager of strategic accounts.

Q: What do IIC and STC ratings mean as far as a product’s performance goes, and why is the Delta of these ratings so important to understanding what these products can achieve?

Utley: “There are two main types of sound to control: the Sound Transmission Class (STC) for Airborne Sounds, and the Impact Insulation Class (IIC) for Impact Sounds.

“Airborne Sound is normally controlled with mass and open cell insulation. Examples of Airborne Sound would be voices and music which travel through the air. Impact Sound is controlled by reducing vibration. Examples of Impact Sound are footsteps, moving furniture, or things dropped on the floor surface.

“When looking at manufacturer’s IIC ratings, it is important to understand how the rating was achieved. Was the underlayment tested by itself, or did the testing include multiple layers, drywall, etc.? The Delta IIC rating paints a more accurate picture and helps to compare sound qualifications.”

Moste: “A flooring material’s effectiveness at preventing the transmission of impact noise is measured by its impact insulation class (IIC). The higher a floor’s IIC rating, the better impact sound insulation it provides. Code requirements for flooring in multi-story buildings in many cities are a minimum of a 50 IIC and some as high as a 55 IIC.

“Delta is commonly misunderstood.  Delta is a Greek symbol (a triangle) typically meant to represent change. The value of the Delta rating is that it isolates the rating of the flooring products, while STC and IIC ratings are representative of the entire floor/ceiling structure tested (flooring and underlayment and concrete slab and ceiling, for example).

“The flooring industry only measures Delta on a 6” slab, which is why we don’t see Delta ratings for flooring on an 8” slab or on a wood truss assembly. In the case of sound-mitigating underlayments, the Delta is the change, or difference, between a bare slab’s IIC rating and that of the same slab with the flooring assembly above it. So if the bare slab has an IIC of 28, for example, and the flooring covering assembly (with the sound underlayment, adhesives and finished floor-covering) achieves an IIC of 50, then you know that the flooring covering assembly alone has a Delta IIC of 22 (50 minus 28).”

Cunningham: “Laticrete feels that Impact Insulation Class (IIC) ratings are a better measurement of sound reduction for cement surfaces. By operating a tapping machine with steel-faced hammers, an acoustic lab evaluates the sound-insulation properties of a building’s elements to determine the effectiveness of floor coverings in reducing impact sound transmission through concrete floors. For a basic concrete subfloor with no resilient underlayment, the IIC ratings are around 28 to 35 IIC. For a basic wood structure with no resilient underlayment, the ratings typically fall around 40 to 45 IIC. Without the addition of sound isolation products, the IIC rating of basic wood structures will rate better than concrete structures because they are naturally more resilient.

“Out of the two types of IIC numbers (IIC or Delta IIC), the Delta IIC number is the most straightforward and is determined through ASTM E2179, which measures the sound performance or difference of two floors.”

Petit: “Building code standards such as the Uniform Building Code (UBC) and the International Building Code (IBC) have developed minimum requirements that floor/ceiling assemblies must achieve for multi-family construction. The minimum value an assembly must achieve is an IIC and STC of 50. As a result, IIC and STC ratings are determined through accredited independent laboratory testing facilities using test methods developed in accordance with ASTM Test Methods. The higher the IIC and STC the better the sound attenuation of the system.”

Jenkins: “IIC values can range from as low as 25 for lightweight residential construction with no floor covering to more than 65 for commercial construction with carpet. More typical values fall between 35 and 55. For multi-family structures, some codes require an IIC of 50 or higher when tested in the laboratory and 45 or higher when tested in the field. Both STC and IIC are methods to test the entire system, including floors, walls, and ceilings.”

Jackson: “Field tests for impact sound (FIIC) and for airborne sound (FSTC) are also recognized by the International Building Code. These sound tests utilize the same testing methods as IIC and STC but are conducted on an actual jobsite in a building upon completion of the flooring installation. The IBC suggests ratings of 45 or higher for FIIC and FSTC testing.

“The Delta rating is another component to measuring sound control properties. This test values the difference between two IIC tests conducted over the same concrete subfloor. One test utilizes the bare concrete subfloor and the other is over the concrete subfloor with floor covering material, underlayment and adhesive included. The importance of the Delta rating essentially revolves around the ability to measure the added sound control properties that the installation solution adds to the installation.”

Lee: “IIC and STC ratings measure how well sound transfer is reduced through a solid building component. The rating system is important because it allows you to assess what the overall performance of your selected assembly should be. It does not however necessarily provide apples-to-apples comparison between products. This is where a Delta IIC measurement is beneficial.

“The intent of a Delta IIC measurement is to quantify the performance value added by a particular product. Test method ASTM E2179 describes the Delta IIC as “the laboratory measurement of the effectiveness of floor coverings in reducing impact noise from a standard tapping machine through concrete floors.” As with IIC and STC ratings, the Delta IIC should be seen as one of several tools used to compare products. Elements of ASTM E2179 leave room for interpretation, which creates a certain amount of variability in the results.”

Erickson: “To compare impact sound control performance of individual products, look for Delta IIC values obtained according to ASTM E2179. These values represent the contribution of the floor covering assembly (everything above the subfloor) to the impact sound rating of a concrete floor. The greater the Delta IIC value, the greater the product’s impact sound reduction contribution.”

MacDonald: “The IIC rating refers to sound that is initiated when someone impacts the floor (as in walking). It is most critical when using a hard surface floor covering like ceramic or vinyl tile. The STC rating is sound that is initiated in the air like speech and music. The one that is more critical is the IIC, as it is more difficult to get the IIC to an acceptable level unless the floor covering is a carpet and pad. As the Delta rises, the sound transmission goes down. The goal is to provide a system with the highest possible STC and IIC at a reasonable cost.”

Q: What are some best practices for working with sound reduction products?

Utley: “Always use products recommend by the manufacturer and follow their guidelines for a successful installation. They most often recommend products like perimeter isolation strips or acoustical caulks. Installers have to trust these recommendations and diligently follow the guidelines.”

Moste: “Know your city’s code requirements and what minimum IIC and STC ratings a product has to meet before selecting a sound mitigating product or system. Site test the material. Because of compatibility between products, know that using systems by the same manufacturer is the best way to achieve the desired results.

“Read the membrane manufacturer’s acoustical lab report in detail; don’t just go by the numbers on the technical data sheet. Carefully follow the membrane manufacturer’s written instructions regarding seam transitions and mandatory gap requirements around perimeter walls and interior columns.

“The membrane manufacturer may not offer a product or solution for handling room penetrations, floor openings and gaps between membrane sections. However, if these areas are left untreated, expect noise complaints.”

Cunningham: “Laticrete manufactures several sound reduction products to meet a variety of IIC ratings, including peel & stick mats, thick glue-down mats and sound and crack adhesives. It’s important for the installer to design their system so that the sound isolation product is as close to the tile or stone as possible, as these types of products perform best when they are close to the finish flooring or the impact sound source.”

Petit: “Know the building structure, including the thickness of the concrete substrate, the spacing of the joists in a wood substrate and if there is any type of ceiling assembly between the floors. When installing flooring over sound membranes, be sure to leave a 1/16” to 1/8” gap at the perimeter location and at any fixed objects like cabinets or bath tubs. Use a non-hardening acoustical sealant or a color-matched acoustical sealant instead of grout to enhance the ability to abate sound at the perimeter and up against fixed objects. Additionally, review the laboratory testing of a system to understand how the sound ratings were achieved and how it relates to your installation.”

Lee: “When installing a sound control mat, there are three tips to remember.

“Be sure to gap or isolate the sound control mat and flooring from walls and vertical penetrations (pipes and columns, for example) to avoid the creation of flanking paths. A flanking path is an indirect path which allows noise to travel along from one space to another. When the sound mat or flooring makes contact with a wall or vertical penetration, a flanking path is created. Maxxon recommends the installation of isolation strips around the room perimeter and all vertical penetrations through the floor. The sound mat and flooring can then be installed up to the isolation strip without fear of creating a flanking path. Alternatively, the sound mat and flooring can be installed with a 1/4” gap around all walls and penetrations.

“Avoid the use of staples, nails or screws. Instead use a manufacturer-approved adhesive if the flooring will be attached, or opt for loose laying the sound control mat if the flooring will be floating.

“Address mat damage prior to flooring installation. If tears or punctures occur, it is important to fix these tears or the sound control benefits will be compromised. Fixing the tear or puncture is as simple as rejoining the torn pieces or covering the puncture with a piece of duct tape.”

Erickson: “As a first step, it is important to identify the floor assembly’s required performance before choosing any particular sound reduction products. Whether it is exceeding code requirements for sound control or other functions such as waterproofing or uncoupling, each underlayment offers its own contributions to an assembly and must be chosen accordingly. Many sound reduction products are multi-functional, and can satisfy multiple requirements while minimizing the overall height.

“To optimize the performance of a given system, the installer must have a good understanding of the installation room and all rooms surrounding that area. Unexpected flanking or sound transmission around the flooring assembly will cause products with high Delta IIC ratings to underperform in the field. To help optimize impact sound reduction performance in the field, isolate the floor covering from neighboring walls or other restraining surfaces with perimeter movement joints. These joints can be filled with acoustical sealant or movement joint profiles can be used as a maintenance-free alternative.”

MacDonald: “Make sure the system you want to use has been tested in a laboratory. Field testing is not reliable from one project to the next. Achieving STC and IIC ratings that are well above the minimum 50 can be done with thicker sound mats and/or multiple sound control products.”

Q: What membranes and adhesives do you offer for sound reduction?

Ardex: “Ardex offers a recycled rubber underlayment in a thickness of 2mm or 5mm, called Ardex DS 70 Acoustic Mat. The DS 70 rubber underlayment is manufactured by grinding up car tires and removing any steel belting and other contaminants, and is FloorScore certified, confirming the production facilities follow rigorous indoor air quality emission requirements. Flooring products that earn FloorScore certification qualify for use in high-performance schools and office buildings. Ardex D S 70 can also contribute toward earning LEED points.”

Custom Building Products: “Custom Building Products offers EasyMat Tile & Stone Underlayment, a versatile mat underlayment that reduces time and labor cost when setting tile and stone over concrete, plywood, primed OSB or any other acceptable subfloor. EasyMat cuts easily with a utility knife, doesn’t require any nails or screws, and comes in a peel & stick version. The product was specially designed so the mortar locks into the mat to create a strong bond throughout the system that will withstand repeated stress and still maintain its bond strength. EasyMat also features SoundGard Technology, which provides high and credible impact sound reduction.”

DriTac: “DriTac is excited to introduce an expansion to our successful line of flooring underlayments with DriTac EnviroTread high-performance rubber underlayment and acoustical barrier, available in 2mm (8402), 5mm (8405) and 10mm (8410) thicknesses. EnviroTread is ideal for successful glue down and floating installations of hardwood, carpet, carpet tile, ceramic tile, stone and laminate flooring. EnviroTread is suitable for both residential and commercial applications.

“This durable rubber underlayment boasts anti-crush mechanical properties and the ability to diminish minor floor irregularities. While installers have the option to float this underlayment, EnviroTread also offers DriTac’s Dual Force, Silent Fuse technology when utilized in conjunction with approved DriTac flooring adhesives in ‘double-stick’ glue-down applications. The resulting Total Sound Reduction System (SRS) features an enhanced lifetime warranty from a trusted, single-source supplier.

“EnviroTread is made from 100% post-consumer waste and is VOC compliant.”

Laticrete: “Fracture Ban is a high-performance, pliable, lightweight peel & stick membrane designed for use under wood, tile or vinyl floors. This reinforced, high-strength membrane performs as an anti-fracture and acoustical underlayment system that eliminates the transmission of stresses from the substrate while dampening the transmission of impact and airborne noise through the floor to the room below

“Specifically when used under tile, 125 Sound & Crack Adhesive provides incredible sound transmission protection while simultaneously protecting the tile or stone finish from any cracking from the substrate through to the tile or stone finish.  Additionally, 170 Sound & Crack Isolation Mat is a high-performance acoustical underlayment system that muffles impact noises under wood, tile or vinyl floors.”

MAPEI: “MAPEI offers a comprehensive line of sound mitigating products for all types of flooring including the most popular, which are ceramic tile and stone, wood flooring and luxury vinyl plank. Our line includes Mapeguard 2, Mapesonic 2, Mapesonic RM, Mapecontact SRT, Ultrabond ECO 985 and Ultrabond ECO 995.”

Maxxon: “Maxxon’s Acousti-Top is an excellent solution for renovation projects or concrete new construction looking to achieve sound code. Acousti-Top is lightweight, thin and at 708 sq. ft., offers exceptional roll coverage. Made from a propriety blend of acoustical fibers, Acousti-Top is highly durable, discrete, and compatible with virtually any floor covering.”

NAC Products: “NAC offers two sound abatement membranes: Super SAM 125 and SAM 3.

“Super SAM 125 is for installations where there is no acoustical ceiling. In addition, Super SAM will provide crack isolation protection for up to 3/8” of lateral substrate movement and can function as a waterproof membrane when a urethane sealant is applied to the seams and end joints.

“SAM 3 is for installations where there is a sound-rated ceiling assembly or some type of an acoustical assembly between the floor and ceiling. SAM 3 will also provide crack isolation protection for up to 3/8” of lateral substrate movement and can function as a waterproof membrane when a urethane sealant is applied to the seams and end joints.”

Schluter: “Schluter-DITRA-HEAT-DUO reduces sound transmission in addition to integrating electric floor warming. It also provides the core functions associated with DITRA: uncoupling, waterproofing, vapor management and load support. The dual benefits of reducing impact sound transmission and providing faster warm-up times make this membrane ideal for hard surface floors in multi-story residential construction.

“To reduce the potential for flanking, Schluter movement joint profiles can be installed in the room at all perimeter joints. Schluter-DILEX-EKE and DILEX-KSA feature a soft movement zone, preventing a sound bridge from forming between the floor covering and the neighboring structures while providing the key functions of a movement joint profile.”

Schönox HPS North America: “At a thickness of just 1/8”, Schönox TS improves impact sound insulation by up to 17 decibels. It’s a resounding difference you’ll notice but thankfully won’t hear. Schönox TS is made of cork and recycled urethane granules and provides additional thermal insulation as well.

“The Schönox Renotex 3D System is a self-bearing, fire-rated construction following the relevant standards of construction in the Multi-Family, Student Housing and Senior Living markets.”

USG: “USG offers our Levelrock brand SAM (Sound Attenuation Mat) Series sound mats. In recent years, in order to get cost-effective higher Deltas, we have added a fabric under our Levelrock brand SAM mats to improve the sound ratings by up to 5 IIC and STC points. This is like getting two sound mats in one.”