Welcome to the second part of our deep dive into sound control products. Last month, we looked at the testing protocols for IIC (impact insulation class) and STC (sound transmission class) ratings, and shared a brief overview of some of the sound control products available on the market. This month, we continue our look at sound control ratings, and ask manufacturers to share what installers/contractors should look for when selecting a sound control underlayment. We end with another roundup of products.


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What the ratings mean

For those who did not see last month’s issue, STC measures sound transmission through the air (laughter, clapping, radios, etc.) while IIC measures impact noise (footfalls, dropped objects, chair scrapes, etc.) However, that’s only part of the story.

Hal Stuhl, Accella Performance Materials vice president and business unit leader, stated: “The STC rating defines how well a floor/ceiling assembly reduces airborne sound by measuring the sound absorption at different frequencies based on the ASTM E90 standard. The IIC rating defines how well the floor/ceiling assembly reduces impact sound by measuring sound absorption of simulated footfalls using the ASTM E989 and E1007 standards. The results of these tests can vary greatly depending on the floor used, type and thickness of the underlayment, ceiling assembly and structure of the building itself.”

Beth Lee, marketing at Maxxon, noted that “the International Building Code (IBC) requires multifamily buildings to have a minimum design rating of 50 STC and IIC. The IBC also recognizes that a design rating (obtained in the laboratory under carefully controlled conditions) is seldom achieved in the field (F) and therefore lowers the required minimum field performance to an F-STC and F-IIC of 45.

“It has been observed that meeting code minimum for STC and IIC performance does not guarantee acoustical privacy or that no complaints will be received. Therefore the authors of the IBC, the International Code Council, have issued an appendix to the code called ICC G2-2010 Guideline for Acoustics. Within this Guideline, the ICC has confirmed that code levels are not acceptable levels of sound control, and they go on to give a recommendation of how ‘Acceptable’ and ‘Preferred’ sound control systems should perform in both lab and field scenarios. Acceptable performance in the field is 52 F-STC/F-IIC, while preferred performance is 57 F-STC/F-IIC. Acceptable performance in the lab is 55 STC/IIC, while preferred performance is 60 STC/IIC.”

Steve Gleason, Homasote’s sales engineer, technical department, went further into how the tests work. “Structure-borne sound tends to be the greater concern in multi-family construction. It is measured in a sound lab under very strict ASTM standards with the use of a tapping machine that is placed on the floor of a sealed assembly. The sound is measured from below and registered in frequency bands from 125 Hz to 4,000 Hz.

“The IIC tapping test does not, however, tell the entire story. It will be accurately measuring higher frequencies while some of the low frequencies, such as footfalls, go unmeasured as they are emitting frequencies that are lower than the test parameters. The design and construction of the entire assembly is very important, but the deployment of a good sound attenuation component as a secondary subfloor is crucial to achieving those code-compliant ratings.”

Jim Wink, vice president of sales and marketing for Foam Products, said to be wary of taking any test results at face value. “There are several acoustical testing labs in the U.S. that test using 6”-8” concrete subfloors and various methods of wood joist/plywood/gypcrete subfloors. Some subfloors have insulation below the subfloor, which create higher IIC/STC numbers. However, most of the current and new building constructions do not add insulation under the 6”-8” concrete subfloor, so buyer beware.

“Also, underlayment manufacturers can create higher IIC/STC numbers by using thicker flooring and denser aged concrete when testing. To create a level playing field, the Delta IIC test was developed to use the same quality/thickness of flooring and subfloor with the tested underlayment. This measures the underlayment decibel IIC rating by removing the flooring and subfloor IIC numbers. Most underlayment companies only publish the IIC/STC ratings with the insulated subfloor test, while Foam Products always publishes both insulated and non-insulated subfloor tests.”

According to Larry Lyons, Amorim Cork Composites’ director of sales and marketing for flooring and construction products, STC ratings are influenced by the mass of the building, not by the flooring or underlayment. “Sound control underlayment products and finished flooring materials do not contribute anything measurable to STC sound reduction; they only address impact noise.”

He noted that an underlayment used with a floor that’s bonded to the substrate will deliver two to three more IIC points than a floating floor installation. Other considerations must be taken when calculating IIC ratings as well.

“Sound-rated ceiling assemblies are not standardized, so get the full construction detail of any test data you are considering that has a sound-rated or suspended ceiling assembly. Field test data (F-IIC) is generally not a good standard of comparison. However, Delta IIC data can be useful in calculating non-standard assemblies.”

Bill Devin, Regupol business unit manager, added: “A common mistake is to think that the IIC number is only based upon an underlayment. An IIC number is based upon the complete floor/ceiling assembly, not just an acoustic underlay.”

Choosing the right underlayment

Kristin Fritts, H.B. Fuller Construction Products’ director of marketing, said contractors should look at the key performance attributes of an underlayment before selecting one. “For example, how well does the product perform with the substrate, flooring and in the specific job environment? In addition, consider how easy the product is to use and clean up, how safe it is for the installer, and whether it eliminates steps or otherwise reduces installation time. Finally, consider the warranty and reputation of the manufacturer in supporting installers in case of a question or problem.”

Deanna Summers, MP Global Products marketing specialist, also has a checklist for contractors to consider. “After sound considerations, contractors should start to look at other performance principles like the type of subfloor, moisture protection, compression resistance (the higher the number, the more supportive it is for a click system), whether or not the underlayment offers any thermal insulation for flooring, its recycled content, and how it contributes to clean air quality.”

Stuhl believes rubber underlayments are the best option for sound control. “A rubber product has superior sound absorption as well as resiliency. An overwhelming majority of commercial underlayment projects are installations using a recycled rubber underlayment, specifically in areas with large numbers of multi-story buildings. Recycled rubber underlayment has proven performance over a longer period of time. The rolled rubber system provides superior compression resistance so you can enjoy its benefits much longer.”

Lee noted that a bit of homework is involved in choosing the best underlayment. “There is a larger-than-expected deviation of results when comparing the exact same assembly’s performance at one lab versus another. The best approach I have seen is to compare lab tests, as well as five or more proven field tests from different projects verifying the average performance levels. If you have the data from all manufacturers being considered for that level of testing, you can make a very accurate decision on a product.

“When it comes to the acoustics on the project you really want to think about the acoustics beyond just one product type. While underlayments and sound control mats make a difference in overall noise reduction, they represent only two elements of the sound control equation.

“Beyond sound control, assembly design is also imperative to achieving a specific UL Fire Rating. Because both aspects are essential in the multifamily housing industry, an emerging trend is the issuance of evaluation reports by reputable third-party organizations. Evaluation reports prequalify all support testing for sound and fire for specific assemblies in one document, which ensures that a specific, well-built design will achieve or exceed fire and sound code.”

Gleason said a contractor needs to weigh the pros and cons of different underlayments before making a choice. “Some popular poured-in-place products can work well, but they come at the cost of the addition of extreme weight and water to the building envelope. Wood-based sound board products are often not strong enough to be used as a secondary subfloor, but a recycled cellulose-based sound board that has been tested for fire under ASTM E119 and has good structural characteristics testing can provide both structural enhancement and code-compliant sound attenuation to a floor/ceiling assembly. There are numerous rubber-based mats on the market, but most of them will only have sound testing over concrete slabs and will not meet code (IBC 1207) over wood member floor assemblies.

“All of those products will have some inherent limitations. It is incumbent upon the designer and/or the contractor to get as much information as possible about the structural components of each possible product as well as their sound attenuation capabilities in order to end up with a quiet floor assembly that lasts.”

Wink noted that it’s also important to understand the characteristics of the substrate and flooring. “Know whether the subfloor has insulation or no insulation below, and the thickness/quality of the wood, laminate or vinyl planks being installed. Request the actual IIC/STC testing from the underlayment manufacturer to compare the different products. Also, realize the many plastic underlayments will compress with traffic on the floor and begin to lose their acoustical benefit. Only high-density underlayments will last and provide the same sound control years after the initial installation.”

Products roundup

Tim Abbott, chief operating officer, Proflex, stated that “our SS-90 elastomeric membrane is an all-in-one soundproofing, crack isolation and moisture control product. It’s the first peel-and-stick membrane to achieve a 50 IIC and 52 STC on a 6” concrete slab with no ceiling. It can be used under approved thin sets, mortars and adhesives for interior and exterior applications of ceramic tile, stone and brick. It may also be used for interior applications of wood flooring.”

Fritts noted: “Tec WoodPerfect Advanced Performance Wood Flooring Adhesive is a recommended solution for sound control under wood flooring. Its many other benefits include one-step moisture control, strong initial grab, crack bridging, an isocyanate-free and lightweight formula, and ease-of-use and ease-of-clean-up. WoodPerfect also offers an advantageous open time of 60-90 minutes.”

Summers said “most of our products are designed with sound control in mind—QuietWalk (94% recycled, fiber-based) for under laminate, floating engineered wood and WPC 4mm or thicker; Insulayment (100% recycled, fiber-based) for under glue down and nail down wood; Sound Buffer for under laminate, engineered wood, luxury vinyl planks and WPC; and Absorbasound recycled crumb rubber-based underlayment for under tile and glue down applications.”

According to Stuhl, “Silent-Tread is our acoustical recycled rubber underlayment product, designed to dramatically reduce sound transmission within a room and floor to floor. It comes in a variety of custom sizes and thicknesses to meet each unique project need. We also supply it with a built-in moisture barrier that rolls out with the underlayment. Silent-Tread can be used with laminate, hardwood, ceramic tiles and engineered wood floor systems. It’s easy to install and does not curl when unrolled.”

Lee shared this about her company’s products: “Maxxon offers a comprehensive line of sound control mats, which includes solutions for wood, concrete, steel frame, open timber and mass timber construction. Most of our Acousti-Mat sound control mats are installed as part of an engineered system of sound mat plus gypsum concrete. This provides permanent sound control and provides substantial STC and IIC improvement. We also offer a low profile topical sound mat, Acousti-Mat LP, that is glued to the subfloor and accepts floor goods installed directly over the sound mat. It is also available with reinforcement for added crack suppression.”

Gleason stated: “440 SoundBarrier is a medium density fiber board that is made from pressed recycled paper and a bit of paraffin wax. 440 is an industry-standard sound attenuation component of a floor assembly. 440 is widely used under all finish floor surfaces.”

Wink said, “Foam Products manufactures the highest-quality acoustical underlayments for all woods/laminates and all vinyl planks/WPC. Eco Ultimate Silencer and Eco Silencer HD FOF are made of high-density polyurethane foam with recycled granulated rubber tire added. These underlayments provide the best acoustical sound absorption for laminates, engineered woods, 3/4” solid woods, bamboo and cork . These underlayments can be used with all types of installation—floating, glue down and nail down. For over twelve years, these underlayments continue to be the leading underlayment for acoustical sound control.

“For over five years, Silencer LVT underlayment has provided the best acoustical sound absorption for all vinyl planks and WPC flooring products with both floating and glue down installations. This underlayment is a high-density constructed polyurethane foam that does not compress and used with all thicknesses of vinyl planks. All underlayments are proudly made in the USA.”

Devin noted: “The Regupol Sonus Underlayments have been specifically engineered and manufactured to control impact noise for use under ceramic tile, stone, solid hardwood, engineered hardwood, laminate and vinyl/LVT flooring. Sonus underlayments have some of the highest acoustic ratings in the industry and are the perfect solutions for condos, apartments, dormitories, hotels, schools or any area where impact noise is a concern. Sonus underlayments are sold in rolls and are available on stock thickness of 2mm, 3mm, 5mm, 6mm, 10mm and 12mm, with custom thickness available.”