OITC, or Outdoor/Indoor Transmission Class, is a rating system used to measure how well a building assembly, like a wall or window, reduces sound transmission from outside to inside, specifically focusing on lower frequencies.
Understanding OITC
The OITC rating system is designed to evaluate the soundproofing effectiveness of building materials against common, low-frequency noises prevalent in outdoor environments. Unlike other sound transmission ratings, OITC takes into account the sound frequencies typical of transportation sources, such as:
- Traffic noise
- Airplanes
- Trains
- Construction Equipment
Why is OITC important?
OITC is crucial because these lower-frequency sounds are often more difficult to block compared to higher-pitched noises, and they are often the most disruptive in daily life.
How is OITC different from other ratings?
While other sound transmission metrics exist, OITC specifically tests the assembly's resistance to lower-frequency sounds.
- Other rating systems might measure sound transmission at higher frequencies.
- OITC is a single number rating which is directly used in building codes.
Key Aspects of OITC:
- Sound Frequency Range: OITC concentrates on lower frequencies, which are harder to attenuate (reduce).
- Practical Applications: It’s relevant for buildings near highways, airports, or busy urban areas.
- Single Number Rating: The higher the OITC number, the better the sound isolation is.
Example
An OITC rating of 40 indicates that the assembly provides a reasonable reduction in outdoor noise levels and will provide better sound isolation compared to an assembly with an OITC rating of 30.
OITC testing
OITC testing involves complex procedures that measure sound transmission loss at various frequencies and calculates a weighted average, providing the single OITC rating value. The test methodology is standardized by ASTM E1332.
Conclusion
In summary, OITC is a vital measurement for assessing the ability of building elements to block low-frequency outdoor noises, particularly those from transportation. The OITC rating allows architects and builders to make informed decisions when selecting materials to achieve optimal acoustic comfort inside buildings.
