Colorado Real Estate Journal - December 2, 2015
In times past, builders used newspapers to insulate walls in homes and to stuff into drafty gaps. If you’ve ever remodeled one of the old Victorian homes you would have found these aged and yellowed newspapers stuffed in every nook and cranny of the exterior walls. Upon examination, you would have discovered that these newspapers were full of advertisements touting miracle elixirs that would cure all that ails you. Even in those times, crafty advertisers realized that the readers are, in general, a gullible bunch. They would believe most anything if it was in print and happened to deal with something they knew little about. Today, we are barraged by new miracle products that claim to do the unimaginable. Some of these products are viable, but it takes a prudent shopper to sift through and find products that actually perform to the level claimed in the marketing or sales literature. Acoustical consultants encounter new products every day that claim hard-to-believe acoustical performances. One of the most common products in this category are those used to mitigate impact sound, such as footfall noise, a common complaint in multifamily housing. Next to moisture issues, sound isolation control is the most litigious problem in multifamily housing. There are two basic measures used in the industry to rate the acoustical performance of a floor-ceiling assembly: Sound Transmission Class and the Impact Insulation Class. The STC is a measure of the performance of the floor-ceiling assembly to isolate airborne sounds, such as voices, televisions, stereos, barking dogs, etc. The IIC is a measure of the floor-ceiling assembly to isolate impact noise (footfall) and other impact noises, such as furniture being dragged across the floor. We have found that achieving acceptable limits of impact sound is usually the most difficult, especially in lighter-weight wood-frame construction. The IIC rating typically ranges between a low of around 20 to a high of 80, with 20 being very poor and 80 being excellent. Suspicious advertising. A simple search on the Internet for impact sound insulation underlayments lead to the following product literature verbiage. The product name has been disguised for obvious reasons. This product is 0.08 inches thick and is described on the manufacturer’s website as, “(This) underlayment is the most technologically advanced flooring underlayment available. (This underlayment) is acoustically superior to all the underlayments.” It goes on to state for this particular product, the Impact Insulation Class equals 72. With a limited knowledge of IIC, except that some building codes call for a minimum of 50, the temptation to hurriedly specify this product with its remarkable impact-sound insulating performance (72) could be almost irresistible. But, wait a minute. Let’s examine this boast of impact sound insulation performance before we rush to get it into the floors of our project. First it needs to be understood that it is not the underlayment that has been found to have an IIC rating. An impact-sound insulation test is conducted on a complete floor-ceiling assembly. That is, the assembly being rated consists of the surface or finish we walk on, down to the ceiling below. One should ask what was the floor finish tested. Was it carpet and pad? Was it ceramic tile or marble? Was it an engineered wood floor or tongue and groove? Next we should ask what was the structural floor. Was it 8-inch-thick concrete? Was it formed-in-place or pre-tensioned or post-tensioned? Was it lightweight concrete on plywood or OSB subflooring on wood joists? What was the joist spacing? We also need to know about the ceiling. Was the assembly tested with or without a ceiling? Was it resiliently suspended or rigidly attached? Was it acoustical tile, one layer of gypsum board, two layers of gypsum board, etc.? What was the depth of the ceiling cavity? Was there fiberglass or mineral wool in the ceiling cavity? All of this information would be available in the laboratory test report and, based on this information, a designer could determine if the floor-ceiling system tested was appropriate for his or her project with respect to impact isolation. It has been our experience that, more often than not, when a copy of the test report is requested from the manufacturer of these unbelievably high IIC performing underlayments, they are not provided. The manufacturer is unwilling to release the very information an architect, designer or consultant needs to evaluate and validate the acoustical claims of the underlayment given in the marketing and sales literature. Beware. Whenever the designers (architects), developers or owners of multifamily residences are concerned with impact noise from the occupants above, adequate acoustical separation is paramount. Many new homeowners have certain expectations of how much they expect to hear from their neighbors located only inches away. If you Google “floor-sound-insulation,” you will get a multitude of products whose advertised acoustical performance appears too good to be true, and there is a good chance it is. The achievement of adequate sound insulation (airborne or impact) in a multifamily dwelling can be a difficult feat and there are usually no easy solutions.