Code: IIC rates a floor/ceiling assembly's
ability to block impact 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
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
UBC requirements for floor/ceiling assemblies: IIC ratings of 50 (if tested in a
laboratory) or 45 (if tested in the field*).
* The field test evaluates the dwellings actual construction and includes all sound paths.
- Impact Insulation Class (sometimes referred
to as Impact Isolation Class) measures a floor/ceiling assemblys
resistance to the transmission of structure-borne or impact noise.
IIC Strength: Helps to rate structure-borne
noise such as footfall, a chair dragging on the floor, or other
realistic sounds in a single number.
IIC Weakness: Due to the nature of the testing procedure,
almost any assembly with carpet will meet the IIC requirement. Meeting
the IIC requirement does not ensure the control of footfall noise.
Conversely, if an assembly does not meet the IIC requirement, it
does not necessarily mean that there will be a footfall noise issue.
The tapping machine frequently used for this test is not designed
to simulate any one type of impact, such as a male or female footsteps,
nor to simulate the weight of a human walker. Thus the subjectively
annoying creak or boom generated by human footfalls on a limber
floor assembly may not be adequately evaluated by this method (American
Society for Testing and Materials ASTM, E 1007, 5.2).
Recommended Isolation Level
An IIC rating of 50 will satisfy the building code requirements.
As with STC, it is typically argued that luxury accommodations require
a more stringent design goal. Bare in mind, some floor assemblies
rated as high as IIC 70 could still transfer noticeable footfall
This code is often used in conjunction with Sound
Transmission Class (STC).