Impact Isolation Class

The IIC is a single number rating system that indicates the amount of impact noise isolation provided by a floor/ceiling assembly system.

Foot noise generated from the floor above a ceiling will transmit structural energy down through the separating I-Joist beams, metal decking or concrete slabs to the room below. Floor underlayments are products that are designed to lift and separate the floor’s surface above from the ceiling down below. The separation point will serve to disconnect the rooms, decoupling the foot noise and other impact sounds that would otherwise work to vibrate energy through.

The IIC scale mirrors the STC scale as outlined in our STC course here at the Academy. The Uniform Building Code will typically require an IIC field rating of 45 or greater for sound isolation between floors in most hotels, motels, apartments, town homes and condominiums. Luxury units will carry IIC values of 55 or greater. As we outlined in our course on Decibels, these numbers are algorithmic. A change of 10 doubles the sound insulation properties. A 60 IIC rating is twice as good as a 50 IIC rating.

For new build or remodel applications, installing floor underlayments is a natural remedy for sound proofing against unwanted foot noise.   The treatment is available with a product called FloorFighter.  But with existing facilities where raising the floor or installing underlayments is not possible, your alternative is to lower the ceiling down below through the use of our dB-Bloc barrier material and the disconnection techniques outlined in our Ceilings chapter of our Applications Guide. Either technique will serve to help disconnect structure and control the transmission of noise.

See FloorFighter Back to Sound 101