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A townhouse owner recently contacted me complaining about neighbor noise and wanting to know if the walls could be tested to determine if they were in compliance with the building code. Of course, they can be field-tested but such testing is expensive and should not be necessary.

After explaining the building code to her she contacted her city building inspection department and received the following reply:

“STC field testing is not required if the contractor provides a “listed system” that meets the 50 STC rating. Most town homes in ××××× ×××××× are constructed with two “one hour” rated walls and most of the one-hour rated walls have a rating of 45-50; so with two walls the rating is 70-100. The code only requires a rating of 50 between units, not for each wall. Field tested walls only require a rating of 45.”

It seems like the building inspector has fallen prey to the notion of adding up the decibel performance figures. Two 50 STC rated walls installed side by side do not equal 100 STC, far from it, the combined performance data is likely only to result in a total STC of 50-53 STC. While the combined performance will be within the building code compliance requirements, doubling the cost of the wall by using a double wall assembly hardly seems a cost effective solution.

Very few building inspection departments insist on field-testing in accordance with the building code as a means of validating the sound isolation of party walls, relying instead on the selection of appropriate listed walls in the architect’s specifications. The fact that the architect specifies a party wall with an appropriate STC rating is no guarantee that’s what he/she will get. It is not surprising therefore to see so many unhappy owners complaining about the noise from neighbors. Many Drywall installers have a nasty habit of jacking up the drywall tight against the ceiling thereby leaving a void between the floor and the bottom of the gypsum board, which will be out of sight once the baseboard, is installed. If this void is not suitably caulked in an absolute airtight manner a 50 STC wall can let enough sound to pass through that can reduce the STC to 39 with as little as a 1/64″ crack.

Drywall installer’s often-times are not sufficiently knowledgeable about the subtle techniques of good sound control and furthermore there are no guidelines in the specifications to guide the installer. Many times the problem may be due to an uneven floor or a warped base plate. A field inspection during construction by a competent acoustician or field test following construction is the only way to insure sound privacy compliance with the building code.

A new homeowner would do well to ask the tough questions regarding noise control ahead of time as they will put the contractor on notice of the owners expectations were sound privacy is concerned. If noise control turns out to be a problem after occupancy there are many soundproofing products and techniques available but no easy fixes so an ounce of prevention before hand can be worth a pound of cure later on.

Whether noise control is accomplished during initial construction as an after occupancy problem or during the process of renovation, Acoustical Surfaces, Inc., has the products and the technical experience to help identify and STOP your acoustical, soundproofing or noise control problem.