What is STC and IIC in insulation and sound specs, and how can insulation influence them?

• A. STC measures airborne sound transmission; IIC measures impact sound transmission; insulation adds mass and damping to improve STC/IIC.
• B. STC and IIC measure thermal resistance.
• C. STC measures moisture content; IIC measures air leakage.
• D. STC and IIC are unrelated to insulation.

Answer: (A)

STC and IIC are building acoustics ratings that quantify how sound moves through structures. STC measures how well airborne sound is blocked between spaces, while IIC measures how much impact noise, like footsteps, is transmitted through floors and partitions. Insulation influences them by adding mass and damping to the assemblies: more mass tends to reduce sound transmission, and damping helps dissipate vibrational energy that would become sound. So using insulation in walls and ceilings, along with damping layers or decoupled, floating details, can raise both STC and IIC, though the exact gains depend on the specific construction and installation. Choices that reference thermal resistance, moisture, or air leakage describe different properties and aren’t what STC/IIC measure, so they don’t fit.