Code: STC rates a partition's or
material's ability to block airborne sound.
Enforcement: Appendix
Chapter 35 of the ’88 and ’91 UBC, Appendix Chapter 12, Division II
of the ’94 and ’97 UBC will be contained in the forthcoming IBC. Although
not all municipalities have adopted this appendix chapter, it is still recognized
as an industry standard.
General Information: The Uniform Building
Code (UBC) contains requirements for sound isolation for dwelling units in Group-R
occupancies (including hotels, motels, apartments, condominiums, monasteries and
convents).
UBC requirements for walls: STC
rating of 50 (if tested in a laboratory) or 45 (if tested in the field*).
UBC requirements for floor/ceiling assemblies:
STC ratings of 50 (if tested in a laboratory) or 45 (if tested
in the field*). * The field test evaluates the
dwelling’s actual construction and includes all sound paths.
Definitions: - Sound Transmission Class
rates a partition’s resistance to airborne sound transfer at the speech frequencies
(125-4000 Hz). The higher the number, the better the isolation.
STC
Strength: Classifies an assembly’s resistance to airborne sound transmission
in a single number.
STC Weakness: This rating only assesses isolation
in the speech frequencies and provides no evaluation of the barrier’s ability
to block low frequency noise, such as the bass in music or the noise of some mechanical
equipment.
Recommended Isolation Level
An assembly rated
at STC 50 will satisfy the building code requirement, however, residents could
still be subject to awareness, if not understanding, of loud speech. It is typically
argued that luxury accommodations require a more stringent design goal (as much
as 10dB better – STC 60). Regardless of what STC is selected, all air-gaps
and penetrations must be carefully controlled and sealed. Even a small air-gap
can degrade the isolation integrity of an assembly.
This code is
often used in conjunction with Impact Insulation Class (IIC).
For more information on Sound Transmission Class, visit STCratings.com.
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