Sound Transmission Class (STC). Impact Insulation Class (IIC). And even Delta versions of these ratings. This oftentimes competing and confusing information has the capacity to overwhelm when assessing the best sound control product for a flooring installation. Which ratings should contractors go by? How are they measured? What do they really mean?

We asked manufacturers in the segment to weigh in. They responded at such a high volume that we’ve decided to split this story into two parts over the next two issues. We hope this deep-dive into sound control helps clear up some confusion about how these products are tested and how they are designed to perform.

Testing protocols

According to Wade Verble, DriTac’s vice president of business development, “IIC tests the ability to block impact sound by measuring the resistance to transmission of impact noise, such as footfall noise. STC evaluates the ability to reduce airborne sounds, such as voices, stereo systems and TVs. Ratings of 50 or above for both the IIC and STC sound tests will satisfy the minimum requirements of the International Building Code (IBC).

“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 in an actual building after the floor installation is completed. The IBC suggests ratings of 45 or higher for FIIC and FSTC testing.”

He added, “Another well-known test is the Delta test, which basically consists of two IIC tests conducted over the same concrete subfloor. One test is over the bare concrete subfloor and the other is over the concrete subfloor with the floor covering material and underlayment included.”

Sonny Callaham, Royal Adhesives & Sealants technical product manager, stated that both the STC and IIC tests follow ASTM standards. “STC is measured in a laboratory using ASTM E490. IIC is measured and stated in accordance to ASTM C634, E90, C423, E 548, E 717 and E 989. It is tested in a laboratory via ASTM method E492-90.”

Steve Taylor, Custom Building Products’ director of architecture and technical marketing, had this to say about IIC and STC tests: “IIC is measured in a laboratory in a room of a specified measurement, without furniture and openings. When the floor is struck with the testing equipment, the test measures the amount of sound that is transmitted through the floor into the room below. STC measures the amount of airborne sound that will permeate the walls and floor of a room in the laboratory. STC is primarily affected by the mass of the wall and floor construction; the membrane under the flooring has little impact on STC reduction.”

He added, “Over the years, expected sound reduction targets have been inflated by builders and owners, because the actual sound reduction did not match the manufacturer’s claims. The ceramic tile industry addressed this by establishing ANSI A118.13 for bonded sound reduction membrane. Products that meet this standard will deliver the claimed sound reduction.”

Sean Boyle, Laticrete’s vice president of marketing, North America, explained the IIC test in detail. “To conduct the test, two vertically adjacent exam rooms—the source and the receiver—are installed and only separated by a standard concrete floor. Designed so the only significant sound radiation entering the receiving room is from the concrete floor, a tapping machine strikes the test floor material and generates sounds between 125 to 4,000 Hz. The acoustic lab engineer plots the results of each tap on a graph, compares the results to the reference assembly and then determines the IIC rating from comparing these two tests. The IIC rating with the higher number shows the better performance.”

He added, “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. Essentially, the Delta IIC test shows what the product adds to the assembly in terms of isolating impact footfall noise—for example, one with a sound reduction product on it and one without. The Delta IIC rating is the performance gain between the first and second test, with the higher number showing better performance.”

According to Mark Lamanno, technical market manager for Franklin International/Titebond, laboratory testing will only give a partial picture of a product’s performance. “Tests are conducted using 9/16” thick flooring, a 6” slab and dead space between a dropped ceiling. Yet, this standard method doesn’t necessarily measure noise reduction in actual jobsite applications. It can be more effective to use other testing methods or to perform site testing.”

Sharon Paley, Ecore International acoustical engineer, said contractors should know that “most acoustical products will never carry their own STC or IIC ratings. These products typically need to be installed in a complete assembly before being tested; therefore any associated ratings are going to be indicative of the entire system and not a single product. For example, this means that no acoustical underlayment will guarantee you an IIC 72 rating by itself, but can help you get there depending on the rest of your proposed assembly such as concrete slab with an insulated gypsum board ceiling below.

“The only sure way to make a fair comparison between competing products is to review their ratings when tested in the same assembly. This means the same: floor finish (porcelain tile won’t perform the same as LVT or engineered wood), adhesive/installation methods (loose lay vs. glued down vs. nailed down), subfloor (6” concrete slab vs. wood joist vs. corrugated deck with gypsum concrete) and ceiling assembly (no ceiling vs. a one-layer GWB ceiling vs. two layers with resilient channels).”

She added, “Exercise caution with Delta IIC ratings (ASTM E2179) as well. While it’s true those should always be conducted only over 6” slab with no ceiling, the standard does not specify a floor finish, which means Product A could be tested with sheet vinyl and Product B with porcelain tile—in which case Product A will most likely have an advantage.”

J. Alex Keene, division manager for Dependable/Keene Building Products, echoed these sentiments. “Contractors need to understand sound ratings are derived from the full system, not simply a single product or floor covering. When choosing an assembly consider a variety of factors. A few good rules of thumb: soft floor coverings perform better acoustically than hard ones, concrete substrates offer greater acoustical performances than wood ones, and an acoustical ceiling is the easiest way to improve performance without affecting the flooring installation.”

Brian Petit, NAC Products’ vice president of operations, also advised caution when looking at a product’s ratings. “Just because a product has satisfactory sound numbers does not mean it is suitable for setting tile, as some products are good for sound attenuation but compromise the ability to install a successful, long-lasting floor. Other considerations should include: how much downtime will [this product] create for the work crew? What is the cost, ease of installation [factor] and warranty?”

Dale Asp, business development manager for Sound Seal’s Impacta division, said both IIC and STC ratings are “dependent on entire assemblies, not any single element. This means that you’ll need to have all the components of your floor-ceiling assembly in order to have an accurate rating. Floor covering, underlayments and the subfloor system (concrete slab vs. wood joist and spacing) are all needed before you can expect real advice from an acoustician.”

David Ford, Stauf USA’s vice president of sales and marketing, advises a skeptical approach to IIC and STC ratings. “Make sure the testing you are reading is from an independent laboratory that is not related in any way, shape or form to the manufacturer that is advertising it. What I have learned is that the numbers can and are fudged with regards to what they are actually registering.”

He added, “The only way to get a truly accurate measurement is on site with onsite testing for that particular job and [sound] insulation. All manufacturers can say whatever they want, but the proof is actually at the jobsite. There are too many variables to take into consideration to make one STC or IIC number accurate on every installation.”

Bostik’s hardwood, resilient and surface preparations systems market manager, Eric Kurtz, noted that “the thickness and type of concrete or wood subfloor structure, whether or not there is a drop ceiling, the type and installation method of the sound abatement product, and even the thickness and type of flooring all make a significant difference in test results. Contractors should seek out specific configurations regarding reported test results so that they can make the best decision for their specific applications.”

Other considerations

According to Jeff Johnson, MAPEI’s floor covering installation systems business manager, “Sound reduction requirements are most often applied to tile and stone installations for multi-unit housing projects. But the same sound control codes also apply to resilient flooring. With the incredible advances being seen in luxury vinyl tile and plank, along with their relative ease of installation, a sound control solution that is proven and documented for resilient flooring will be in great demand.”

Verble noted that contractors should be well-versed in the various product options in the marketplace. “Due diligence on product offerings and the company behind those products will always play a significant role. Premium-grade options from time-tested suppliers that offer warranties in writing can help circumvent future issues and maintain positive results.”

Callaham also cautioned that due diligence needs to be taken when comparing sound control systems simply by their ratings. “Make sure you are comparing the test results to the specific ASTM standards. Over the years, these tests have been modified to increase the sound rating. This can be done in a few different ways— using a thicker concrete slab as the control, adding a drop ceiling assembly or using a test application that will not be used in the field.”

To combat this, “ask for a copy of the sound report from the manufacturers,” he said. “These should be obtained prior to the bid to ensure the flooring contractor can properly relay realistic expectations to the end user. If you are submitting sound results for a product and the test results are achieved using a drop ceiling and your project will not have a drop ceiling, the end result will be much less than expected. Each manufacturer should have a copy of the test procedure from a certified laboratory testing the specific assembly they are promoting.”

Callaham added, “The largest contributor to sound control is the actual building itself. The design of the substrate and the ceiling below will maximize or minimize any benefit from the underlayment or flooring. The flooring contractor needs to make sure that all parts to the system they are installing are compatible and are fully warranted by all parties involved. Too many times the system is put together only to find out that it is not an approved application.”

Asp said a contractor needs to understand their needs when making a decision on what product to pick. “Be sure these needs are reasonable to achieve. There is a lot of misinformation out in the marketplace today. Research the available products for your assembly, then pick one that works best for that assembly. You can get information on the various products by speaking with a sound control testing facility or engineer. We are also available to field calls regarding sound control products, tests or just general sound control underlayment information and requests.”

Alex MacDonald, USG’s manager of strategic accounts, said contractors need to base their product decision on both price and performance. “If they are looking for a permanent, capital improvement to the floor we would suggest our method of using a sound mat underneath one of our gypsum-based self-levelers. This approach leads to a system that will be there for the duration of the structure and not have to be replaced each time a new floor covering is installed.

“To make the selection process easier, USG has published over 150 third-party sound tests in the USG Levelrock Brand & USG Durock Brand Fire and Sound Systems Guide (IG1685) that provides the specific sound test results based on the type of floor coverings that will be used in any given assembly. This reference guide gives the specifier or contractor STC and IIC values so they can quantify the price of the system vs. the sound performance of the system they select.”

Keene noted that “The contractor must determine that the sound rating attached to a product matches the floor ceiling assembly on their project. If each product’s rating matches the project, I would consider other qualities including price. If the project is a tile project I would seriously consider the anti-fracture properties of each product. If one offers me greater protection at a lesser or comparable price, I would select it over the others.”

Other qualities to look for in a product include “moisture control capabilities and warranty against moisture damage as well as ease of both application and cleanup,” said Lamanno.

Paley added, “It’s easy to take acoustical ratings at face value, but try not to. Give yourself extra time to research the best products for your job. Make sure you have the right expectations for your specific project and be cautious of any product that only provides one rating for all scenarios.”

The latest products

We also asked manufacturers to share some information on their latest sound control products. Here are their responses.

Kurtz: “Bostik’s Ultra-Set SingleStep2 product offers IIC ratings as high as 70 in a single application. Ultra-Set SingleStep2 uses Bostik’s proprietary AXIOS Tri-Linking Polymer technology that has exception workability and is easy to clean off of prefinished flooring even after cure. Vapor-Lock is another high performance adhesive and acoustic membrane that is polyurethane-based.”

Taylor: “Custom Building Products recommends EasyMat Tile and Stone Underlayment with SoundGard Technology for most residential and light commercial installation that require impact sound reduction, and CrackBuster Pro for heavy-duty commercial projects that require sound control.”

Verble: “DriTac has unveiled two new underlayment systems: DriTac 8302 Double Impact for engineered wood plank and floating floor installations and DriTac 8301 Impact for resilient floor installations. Both zero VOC products provide enhanced sound control properties and a dual force, silent fuse technology that helps dramatically cut down on sound transmission when used with approved DriTac flooring adhesives.”

Keene: “We offer two sound control underlayments for use under vinyl, wood and ceramic. Our QQ Step Soft is a rubber underlayment designed for use under a variety of floor coverings, including wood, ceramic and vinyl. We also have an uncoupling and acoustical membrane called KeedeRoll MT. We designed MT specifically for ceramic tile, and it offers an extra-heavy rating paired with a 54 IIC rating on an 8” concrete slab without an acoustical ceiling.”

Boyle: “Laticrete Fracture Ban is a high performance, pliable, lightweight peel-and-stick membrane designed for use under wood, tile or vinyl floors. It performs as an anti-fracture and an acoustical underlayment system. Specifically 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. 170 Sound & Crack Isolation Mat is a high-performance acoustical underlayment system that muffles impact noises under wood, tile or vinyl floors.”

Johnson: “MAPEI has combined the use of Mapesonic 2 sound reduction membrane and Ultrabond ECO 360 premium high-performance adhesive into a system for installing luxury vinyl tile and plank. Working together, Mapesonic 2 and Ultrabond ECO 360 make resilient floorcovering installation easier for installers, and specification- and code-compliant for contractors, with much quieter results for the homeowner.”

Petit: “NAC Products has multiple offerings including Super SAM and SAM 3, and in certain installations, our ECB crack isolation membrane can function as a sound abatement membrane depending on the level of sound attenuation the project requires. We mainly provide products for hard surfaces like porcelain and ceramic tile, stone and under hardwood flooring.”

Callaham: “Royal Adhesives offers our Millennium Series IFS 4014 Urethane Adhesive for applications that require adhesive, unlimited moisture protection and sound control in one product. Our patented trowel allows the installer to install the flooring just like they would a traditional wood flooring, but offers the end user both moisture protection and sound control.”

Asp: “Under tile Sound Seal/Impacta offers our ProBase rubber underlayments as well as our synthetic cork product, Cerazorb. For a double glue-down installation we offer ProBase, Cerazorb and our two-ply fast-track system, Jumpax. All of these can also be used under floating wood or laminate floors as well as our products for floating floor only installations: Redupax and Paladin. We also off a product for a nail down 3/4” hardwood floor. That product is Soundeater.”

Ford: “Stauf offers SMP 960 which is a polymer that is for use under wood. We have not [sound] tested other products but we were the first in the industry to have it tested and the first to do the moisture control along with it during the testing phase. Sound control is not a large part of what we have tested, yet I believe if others were tested in our line they would come back with favorable results.”

Lamanno: “Titebond 771-Step Adhesive, Moisture & Sound Control combines the superior properties of a moisture cure adhesive with the ability to be used as a moisture and sound control system, primarily for wood floor installations.”

MacDonald: “USG offers sound mats that go under our gypsum-based self-leveling underlayments. For instance, use the 1/4” USG Levelrock Brand SAM-N25 Sound Attenuation Mat and/or USG Durock Brand Quik-Top Self-Leveling Underlayment poured at 1” over the mat. Quik-Top will make a wood subfloor feel like a concrete slab and at the same time, when used in conjunction with a sound mat, can reduce the sound of foot traffic by about 50 percent.”