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Outdoor-Indoor Transmission Class of Concrete Masonry Walls

CMHA TEK 13-04A

Providing a quality indoor acoustic environment is becoming a higher priority in many cases; particularly in urban environments where noise from traffic and other outside sources can be a significant distraction, especially in schools, homes and the workplace. Concrete masonry walls provide excellent noise control due to their ability to effectively block airborne sound transmission over a wide range of frequencies.

The ability of a wall to insulate a building interior from outdoor noise can be indicated by the wall’s outdoor-indoor transmission class (OITC), with higher OITC values indicating better sound insulation.

OITC is one rating system available to help compare the acoustic performance of various wall systems. Others include the sound transmission class (STC) and the noise reduction coefficient (NRC). Both OITC and STC indicate a wall’s ability to block the transmission of sound from one side of the wall to the other. OITC differs from the STC rating in that the OITC was developed specifically to indicate transmission of noise from transportation sources. STC was developed primarily for indoor noise sources, such as human speech. Unlike OITC and STC, NRC indicates the ability of a wall to absorb sound, which is useful for controlling sound reverberations within a room.

This TEK presents OITC values for a variety of common concrete masonry exterior walls. STC and NRC values for concrete masonry walls can be found in TEK 13-01D, Sound Transmission Class Ratings for Concrete Masonry Walls, and TEK 13-02A, Noise Control With Concrete Masonry (refs. 1, 2), respectively.

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