Insulation and Sound Ratings – STC Ratings

Posted on April 17, 2013


We get this type of question often, “do you have (fill in the name brand) sound insulation?”

The short answer is, “not really.”  Fiberglass batts do not have an STC rating on their own, no matter what the package says it is. STC ratings are indicated for the system, not components of a system. Having stated that, the use of any fiberglass insulation can increase the partition assembly STC rating 4-10 points and we have isles full of product that will accomplish a higher rating.

Sound moves through material and through the air. This post will primarily address sound moving through air and its mitigation using insulation.

When it comes to promoting product for deadening sound, marketing people have done a very good job of convincing us that we need a new product to handle a new issue—Noise. Is this just smoke and mirrors? Not necessarily— Manufacturers are merely pointing out that their material also mitigates sound by promoting the old product as a new product and re-labeling and re-packaging it. It’s just really good marketing! The fact of the matter is; the insulation we and most dealers have in stock, does an extra good job of diminishing sound transmission and it always did.

Sure… there are a few new engineered products like QuietRock (an engineered acoustical drywall) on the market, especially made for controlling sound, but chances are, your customer doesn’t need to invest in that type of expensive noise reduction.

Reducing noise has become a prominent topic in the last few years. Certainly, no one wants to live in or near a building where they can hear loud music or worse, hear a toilet flush — and for those reasons, architects design sound reduction into high-rises, condos and multi-family homes. Good neighbors will soundproof home theater/entertainment rooms against potential complaints and if your teen’s rock band practices at your place… well, it might be a good idea to dampen the sound and keep the peace.

Simplistically speaking, insulation lessens the transfer through the air while the materials used in the structure of a partition determines how much sound vibrates through to the other side. For instance, a metal stud used instead of a wood stud, has less surface to transfer sound and will yield a higher STC in the wall system. Using resilient channel helps break some of the structural pathway sounds will travel.

Fiberglass and mineral fiber insulations were originally designed to insulate and had (perhaps) an unintended benefit of also keeping sound from bouncing back into a room or vibrating through. Sound reducing capabilities have always been there in those products.

Unlike chemicals that may be added to some materials as a fire retardant, there is nothing that is added to insulation to enhance its product for sound absorption. An R11 Sound Attenuation Blanket has no different sound properties than an R11 unfaced roll or batt you might already have in stock. It matters how and what you use for material (structure) in the system that controls sound. No one uses R11 in an exterior wall today, but as a sound insulation relabeled as a sound attenuation blanket for an interior wall? Sure!

All insulation buffers sound and I’m not suggesting there aren’t specialty products—there are. On the commercial side, specialty fiberglass board products are made in a variety of densities and thickness marketed for sound. They also insulate. However, according to testing performed at several independent laboratories—a variation in density has little or no effect on overall STC ratings. Insulation thickness is what drives the bus.

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Written by: Alice Deeny