STC vs. OITC: Which Rating Actually Matters?

Sound Transmission Class (STC) is an integer rating of how well a building partition attenuates airborne sound. In the USA, it is widely used to rate interior partitions, ceilings, floors, doors, and windows. The STC figure very roughly reflects the decibel reduction in noise that a partition can provide. STC is specifically designed to measure speech sounds.

Outdoor-Indoor Transmission Class (OITC) is a standard used for indicating the rate of transmission of sound between outdoor and indoor spaces. Unlike STC, which targets higher-frequency speech sounds, OITC is designed to measure low-to-mid frequency sounds like aircraft, sirens, and heavy traffic noise.

If your project is an interior office partition, STC is the standard. If you are specifying windows for a building near an airport or a highway, OITC is the more critical metric to ensure occupant comfort against low-frequency rumble.