Sounding off about Underlayment, Pt. 2

I’ve blogged a lot about IAQ (Indoor Air Quality), but taking that a step further, we should be looking at the entire IEQ: The Indoor Environmental Quality.

IAQ is part of the IEQ, as is good lighting and temperature control. Smart color choices and the use of natural materials (go wood!) can also help create a positive IEQ. Now sound control is being recognized as a factor as well. It’s called “acoustical comfort.”

Designing for acoustical comfort goes beyond a just picking an underlay—it’s the entire system that matters. What is the structure (steel, concrete, wood frame?), how thick is it, what other insulation is used, are there air pockets, and how about the windows and…?!

In the case of big projects, the full system needs to be studied for maximum benefit. For example, any underlay placed over a 9” concrete slab with a suspended ceiling stuffed with insulation will likely get a good rating – but not many buildings have that kind of construction. So when comparing acoustic ratings you also need to know under what conditions the material was tested.

When LEED looks at Acoustical Comfort, it approaches it from many different directions—you’ll need to look at the exterior sound situation (are you near a highway or an airport?), the operational noises (do you have a noisy HVAC system or rattles in the water pipes?) and the materials selected for sound control. The entire project is often reviewed and when considering flooring, you are generally reviewing the entire system being installed, not just the floor or the underlayment.

When a residential customer looks at sound control, they are rarely able to consider all those features. Most often, they are just looking at underlayment options and it is easy to become overwhelmed. Do I want the cork or the foam? Do I need a moisture barrier? This is thicker but has a lower number? This says it’s better for IIC but what if STC is my issue? Actually, what is IIC and STC? Is FIIC different from IIC?

Let’s try to simplify.

IIC is “Impact Insulation Class.” These are structurally borne sounds. Hear that footstep? That’s an impact sound. The standard showroom display of a dropping golf ball is a familiar illustration for IIC. However remember that a golf ball is not at all the same as a footstep. A laboratory rating for a product may not accurately reflect the actual conditions when installed, where an annoying creak of a joint might give away your teenager sneaking in after curfew, but underlayments certainly may improve an IIC rating.

Hear that shouting? Consider that a factor of what’s known as STC, “Sound Transmission Class.” We’re trying to reduce airborne sounds here–voices, television and that dog barking… Although it is still commonly referenced by flooring companies, STC is most appropriately used for wall and ceiling systems rather than directly for flooring. Underlayments will not usually make significant differences in STC ratings, but again that would depend upon the type of building structure.

Of course STC could come into play if someone in a condo above or below is hard of hearing and they have their TV blaring. The flooring and acoustical underlay could create an insulating layer. In real world, it is most likely the complete subfloor/ceiling assembly that would do this. Like with most features, it’s rare that a single component is going to dominate the end results—it’s the entire package that’s important. So in the future, expect to hear more about “Subfloor/Ceiling Assemblies” in major projects.

You probably have seen the term FIIC or less frequently perhaps FSTC. That “F” stands for “Field,” meaning it’s not a laboratory number, rather it is a test from a real building, directly applicable to that specific building design and construction. That’s logical and easy to remember. Unfortunately, the names for the tests were recently changed by ASTM (American Society for Testing and Materials).

The updated terms are AIIC and ASTC. The “A” replaces the use of the letter “F” and stands for “Apparent” also meaning it represents a field test, rather than a lab test.

The National Laminate Flooring Association advises that:

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. IIC/FIIC and STC/ FSTC tests are essential tools for evaluating sound in multi-level dwellings. However, without knowing and accounting for the whole floor/ceiling structure used in the test, the results are basically meaningless. Using IIC (FIIC) and STC (FSTC) results to represent the sound deadening ability of an underlayment without describing, in detail, the whole floor/ceiling assembly causes confusion at all levels of the marketplace and is ultimately misleading to the consumer.

One last note….sound control is one of the fastest growing segments in the industry. But not only do the technologies (both “hardware” like flooring and underlayment and “software” like the actual structural designs) constantly change, the testing protocols are also improving. Ratings of a few years ago may not be directly comparable to ratings today—test methods are changing regularly. I was advised that pre 1999 STC results posted before 1999 are largely unrelated to today’s results, and that the difference becomes greater as one goes back in time because of radically advances in testing methods.

For more info, try these sites:–14857?source=part

(And my thanks to the patient Metropolitan Spec Team for helping me with this post!)

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