Achieving The Sound of Silence

A common deterrent to personal enjoyment in multi-family buildings is sound transmission.  Often determining what is too loud is subjective and measured by the sensitivity of our ears. The Building Code requires that walls and ceilings meet an STC (Sound Transmission Class) rating of 50 and an IIC (Impact Insulation Class) of 50. STC is related to airborne noise like a television, speech, or music and IIC correlates to footfalls or a dog’s toenails when they impact a tile floor. 

At an STC rating of 50, loud talking cannot be heard but load music can be noticed. We usually are asked to investigate sound transmission concerns in wood framed buildings when the thuds of foot traffic of the resident or their pet, above, is perceived to be disturbingly excessive.  Many condominiums have rules related to the percentage of the floor area that must be covered by carpet.  This is likely because most carpeted floors comply with a IIC 50 sound rating.

Manufacturers of products used to construct wall and ceiling assemblies have their materials tested in a laboratory with various combinations of framing, drywall, and insulation to determine the STC rating.  To inspect a noise concern, our first step is to review the available architectural drawings to determine the intended design and the associated STC rating for the wall and/or ceiling construction. Then we will cut a few holes at inconspicuous places to confirm if the drawings were followed.   Most people are surprised to learn that no insulation was placed inside the wall or ceiling and that many assemblies can achieve the required STC rating without insulation. 

Products are available that can be installed on floors, walls, and ceilings to reduce the offending sound transmission. Installing these materials can be limited to sleeping areas to save cost and the amount of disruption that the project has on a living space.

Satisfactory remediation of a sound problem can be difficult.  Our ears will perceive a reduction in noise by one half when the STC rating is increased by about 10 points. Conversely, anything less than a10 point change is hard for people to distinguish. Finally, any expectation that a once noisy unit located within a multi-family building will become “sound proof” or like a recording studio after remedial work is complete is unrealistic