Noisy Neighbors or Poor Sound Isolation?

Sound isolation refers to the ability of construction assemblies to minimize the transmission of sound and isolate sound within its environment. You may enjoy listening to your favorite band play, but your neighbors may find the “noise” to be unwanted. Construction assemblies controlling sound isolation directly affect the quality of life of townhouse and condominium residents. The distress resulting from poor sound isolation varies with the subjectivity of the unit occupants. A change in neighbors can mean a big improvement or a sudden loss of acoustic privacy. Because of the subjectivity of noise pollution, the standards are set to allow for ranges of tolerances.

Poor sound isolation in multi-family housing, combined with noisy neighbors, has been documented to lead to violence and even death from the disputes that have arisen. Less sensational, but still a great concern to homeowners, is hearing conversations, music, television, footfalls, plumbing, adult activities, and washer/dryer vibration from neighbors. Purchasers of townhouses, condominiums, and luxury housing usually have higher expectations for sound isolation than people occupying rental apartments.

Sound Ratings and Testing

The two most common measurements of sound isolation are the Sound Transmission Class (STC) and Impact Insulation Class (IIC). Both ratings are averaged values of sound isolation through an assembly at a number of frequency points along the sound spectrum. The Sound Transmission Class (STC) measures airborne sound and is used most often to determine the sound isolation of walls and floors. The Impact Isolation Class (IIC) is a measure of structure-born transmission and is the measurement most often used at hardwood, vinyl, stone, and tile floors. All sound tests are controlled by ASTM test methods. Below is a table relating STC ratings to the effective sound reduction experienced by residents.

Noise Control Guidelines and Specifications of Assemblies

The 1997 Uniform Building Code (UBC), Appendix Chapter 12 and the 2000/2003 International Building Code (IBC), Section 1207 require the same minimum standards. For airborne sound ratings at wall and floor/ceilings assemblies, the minimum rating is 50-STC (45-FSTC if field tested). For impact noise at floor/ceiling assemblies, the minimum rating is 50-IIC (45-FIIC if field tested).

Standards for establishing the minimum sound isolation requirements for luxury condominiums, townhouses, and all multi-family residences built in “quiet” environments are provided by the “Guide to Airborne Impact, and Structure Borne Noise Control in Multifamily Dwellings,” HUD TS-24 (1974), Chapter 10; FHA recommended criteria, copyright 1967. While this standard is over 35 years old, it continues to be referenced as the primary source standard for noise control in luxury and townhouse residences. The HUD TS-24 standard sets STC and IIC minimums for townhouses and for three classes of apartments, with Class I being applicable to luxury housing. Minimum ratings are provided for many combinations of adjacencies, depending on room use. Below is a chart showing the sound minimums for the most stringent adjacency requirements.

Causes of Poor Sound Isolation

Deficiencies in the sound isolation of an assembly can occur for any of the following reasons:

1. The building designer does not properly specify or mis-specifies the assemblies. This can be confirmed by a thorough review of the assemblies shown on the drawings. Some architects are unaware of the HUD/FHA TS-24 standard and may have relatively little experience designing luxury-attached housing where a higher level of sound isolation is appropriate. Architects may also allow inappropriate substitutions of materials and methods in the assembly that lower sound isolation performance.

2. The assemblies are modified from those specified in the drawings. This error may occur from a substitution to a different assembly, a substitution of materials, or an omission of assembly components. Most types of “resilient” channels used in construction do not meet the specifications in the published test results. The use of these alternate channel types results in inferior sound isolation performance. Confirmation of these defects after construction can sometimes be found in change orders or requests for information (RFI’s), or even in the subcontractor’s scope of services. This discovery requires intrusive examination of the walls and/or ceiling assemblies after the construction of the finished wall and ceiling assemblies is complete.

3. Construction errors are sometimes made in the assemblies. These errors may include non-sealed or improperly sealed joints and penetrations, improperly installed insulation, improperly installed blocking, and improperly nailed resilient channels. Confirmation of this defect after construction usually requires infrared scans and/or intrusive examination of the walls and ceiling assemblies in the residences.

Sound isolation deficiencies are a common complaint and are generally ranked after inadequate waterproofing as a source of homeowner complaints.

Complaints are also rising, according to Don Neff, President of La Jolla Pacific Ltd., as presented in “Minimizing the Risk of Defect Litigation,” International Risk Management Institute. The solution to avoiding noise problems is for designers and builders to comply with the HUD TS-24 guide when designing and building luxury condominiums and townhouses, as well as apartments located in quiet environments. In addition, assemblies need to be constructed in accordance with the tested assembly to achieve the desired sound isolation performance. Attention to sound isolation in the planning and building stages can save considerable expense and aggravation, as well as preserving goodwill with buyers, rather than making remedial sound isolation repairs once the buildings are constructed.


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