Sound isolation between rooms

Airborne and structure-born sounds between rooms can be managed by specifying architectural sound isolation assemblies that utilize three principles:

Mass of construction materials such as concrete slabs or plywood subfloors.

Airspace between construction components.

Resilient isolation element used to integrate mass and airspace.

Sound Transmission Class (STC) and Impact Insulation Class (IIC) are two performance values associated with sound isolation between rooms.

Sound Transmission Class (STC) is a numerical rating of how well a building partition attenuates airborne sound. In the USA, it is widely used to rate interior partitions, ceilings/floors, doors, windows and exterior wall configurations (see ASTM International Classification E413 and E90.) The measurement is heavily weighted in the 1000 to 4000Hz frequency. Normal speech can be clearly understood through a wall with an STC of 30. At STC 40 speech can be heard with some effort. At STC 60 loud speech is inaudible but loud music can still be heard, especially loud bass notes. The Uniform Building Code (UBC) states that hotels and multi-family units are required to have an STC of 50.

Impact Insulation Class (IIC) IIC is a single number rating that provides a means of comparing the acoustical performance of floor-ceiling assemblies, when excited by impact such as footsteps. The IIC is derived from ASTM method E989, which in turn uses a tapping machine specified in ASTM method E492. A larger number means more attenuation.

Isolating sound reducing blanket of insulation has floor supporting resilient pads. Photo provided by Kinetics Noise Control

A concrete slab covered in roll-out isolation material with resilient pads supporting a plywood and hardwood finish floor increases STC to 66 and IIC to 63. Image provided by Kinetics Noise Control