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That Noise is Driving Me Crazy

A Different Kind of Pollution

Article written by Jack Carr, P.E., R.S., LEED AP, Criterium Engineers
Published in Condo Media, April 2010

Residents, often moving from single-family homes, are not used to hearing their neighbors. Sound transmitted between units, or from outdoors, can be extremely annoying and disruptive, and sound transmission is not always apparent during a walk-through.

If there is a perceived noise problem, first ask from where is that noise coming? Is it coming from outside (highways, airplanes or rail noise)? Is it transitory (construction noise)? Is it seasonal (outdoor activity)? Or, is it an internal noise transferred between units or from common areas into each unit? Transmission between units may be via walls, ceilings or floors, or as a result of mechanical chases or through the actual piping or ductwork.

When addressing noise issues, determine whether the problem is localized or omnipresent. Certain parts of a building (near fans or mechanical equipment, recreational areas, etc.) may be more prone than others to experience problems. We have even found a variation between units due to construction inconsistencies. Field modifications in another area of the same building created a problem.

The biggest factors for sound transmission issues are physical location, construction type and quality, and building age, If a development is built near a highway or a flight path, the resulting potential problems may be obvious and hopefully were addressed during the design stages. Older buildings, especially factory or warehouse conversions, can present particularly difficult problems, Structural components may abet sound transfer allowing it to pass unobstructed from unit to unit.

Some wall and ceiling assemblies are more effective than others, but all must be assembled correctly. Care must be exercised to avoid "flanking paths" that allow sound to get around sound deadening assemblies.

What Is Reasonable?

Often, perception is reality, so, first define the problem. Is the noise that is causing complaints louder or more frequent than the occupants might reasonably expect? It is important to recognize that much of this is subjective. Different people will have different tolerances. The type of noise - music, conversation, toilets flushing - carries with it a relative level of acceptability.

There are some relatively objective standards that have been developed to both quantify sound transmission and define acceptable levels, The Sound Transmission Class (STC) is a value derived from creating and measuring the sound attenuation at various frequencies and comparing that to a standard reference, The STC measures sound transmission between areas separated by a common surface (walls, windows, etc), while the Apparent Sound Transmission Class (ASTC) is a more comprehensive measure that incorporates other pathways of sound transmission such as beams, columns and chases for mechanical and electrical equipment, and is generally the basis for field testing.

Thc STC and the IIC have been incorporated into local code, which specify values of 50 (or 45 if field tested). However, codes are typically minimum levels and may not be high enough to produce comfortable noise control in attached residential units.

Sound energy is best disrupted by creating breaks between spaces. Mass also plays a role in overall comfort. Generally, to improve transmission loss (i.e., the ratio of the sound energy striking the wall to the transmitted sound energy, as expressed in decibels), designers should increase the weight of the surface layers or the distance between the surfaces. Fiberglass insulation is often used, even in interior walls, to reduce sound transmission. Caulks and sealants are often used as well. Building walls in which the studs are offset and penetrations like electrical boxes and medicine cabinets are sealed can improve the conditions. Drywall can be attached with resilient channels. Dampening the source also should be considered. Many associations are beginning to establish minimum coverage of hard floors with carpeting, restrictions on hard-soled shoes and setting limits for sound levels from audio equipment. Other, more sophisticated strategies like baffling can be employed.

Reducing sound transmission in an existing building is much more difficult than including good sound transmission
practice during construction. Reduction of sound transmission in wood framed buildings is generally more difficult than masonry or steel structures. If problems arise, the first steps arc to determine the existence of a real problem, attempt to quantify it, inspect to ensure that components were actually built as planned, and then hire a qualified consultant to recommend improvements.