Today, there are more and more products on the market for providing sound reduction for under Luxury Vinyl Tile and Plank. These products can range from high density foam to a cork/rubber membrane. Upon reviewing products websites, care must be taken when looking for an acoustical underlayment as these sites are stating very high IIC and STC results without showing how and what the floor/ceiling system was used and how the product has been installed. For example, below is information pulled from various sites;
The highest rated and most effective acoustic barrier on the market. Provides unsurpassed through-the-floor and footfall noise reduction (11C 69/STC 66). Excellent Acoustical Performance. IIC Rating 73/STC Rating 67. Rated among the highest in the flooring industry with acoustic rating of IIC71/STC67
Other manufacturers of acoustical membranes will publish information like this;
ASTM E 492, Impact Sound Transmission (IIC) – 55 /ASTM E 90, Airborne Sound Transmission (STC) – 55 with 8” Concrete Slab, No Ceiling Assembly.
There are two types of laboratory sound tests performed in a controlled environment recognized by the International Building Code for sound vibration that travels from one living area to another: Impact Insulation Class (IIC) and Sound Transmission Class (STC). IIC tests the ability to block impact sound by measuring the resistance to transmission of impact noise or structure-borne noise (simulating footfalls, objects dropped on the floor, etc.). STC evaluates the ability of a specific construction assembly to reduce airborne sounds, such as voices, stereo systems, and TV. Both tests involve a standardized noise making apparatus in an upper chamber and a sound measuring system in a lower chamber. Decibel measurements are taken at various specified frequencies in the lower chamber. Those readings are then combined using a mathematical formula to create a whole number representation of the test, the higher the number, the higher the resistance. Ratings of 50 or above for both the IIC and STC sound tests will satisfy the minimum requirements of the International Building Code.
With the various types and combinations of building materials available to the industry, it is not surprising that the sound test results among different floor/ceiling assemblies may vary dramatically. One can imagine sound testing over a 6′′ concrete floor with a 12′′ suspended ceiling attached and filled with 8′′ of fiberglass insulation, as opposed to testing over just a 6′′ concrete slab. The more layers and thickness of materials usually means a higher sound test result.
It is important to note that IIC/FIIC and STC/FSTC tests are not single component tests, but an evaluation of the whole floor/ceiling assembly, from the surface of the floor covering material in the upper unit, to the ceiling in the lower unit. An integral part of a report for any of these sound tests is a detailed description of the floor/ceiling assembly used in the test.
The only way to accurately compare the sound deadening characteristics among underlayment materials using IIC/FIIC and STC/FSTC testing is to keep all other components in the test assembly constant, i.e., the same floor covering material, the same thickness and density of concrete (or composition of wood sub-floor), and the same suspended ceiling assembly. With everything else being equal, one can evaluate different underlayments as to their individual contributions to the sound insulating ability of that whole floor/ceiling structure.
Installation of these products can range from a “Double Glue Down” (both the underlayment and the LVT are glued down, Glue Down Underlayment/Loose Lay LVT, or Floating Underlayment/Floating LVT.
Care must be taken choosing the Glue Down Underlayment/Loose Lay LVT, or Floating Underlay- ment and Floating LVT. These systems must be treated as a floating floor system that requires an ex- pansion zone around all vertical objects, no pinch points such as moldings nailed down into the floor or extremely heavy objects placed on top the Floating Underlayment/LVT system, or areas subjected to heavy rolling loads. This also includes floating underlayment membranes such as Congoleum Underflor. These products contribute very little to IIC/STC ratings and should not be given any consideration for an acoustical membrane.
When using the “Double Glue Down” applications, most of the high density foam manufacturers have their own underlayment adhesive for adhering the foam to the substrate as well as an adhesive for adhering the LVT to the foam underlayment. The cork/rubber manufacturers generally suggest a one type of adhesive to use for adhering both the underlayment to the subfloor and the flooring to the underlayment.
Please note, when installing any flooring product over these acoustical membranes, the flooring may be subjected to damage caused by indentation.