Sound Transmission Class (STC)

A single number rating system used to express the sound transmission loss properties of a wall or roof is the sound transmission class (STC). The higher the STC value, the better a construction reduces the transmission of sound. In a typical metal building construction the values for STC range from a low of about 20 to a high of 55. The STC rating has been in existence for many years and is based on speech sounds.

Outdoor-Indoor Transmission Class (OITC)

Recently a new single number rating has been introduced. It is called the outdoor-indoor transmission class (OITC). It is used to specify the sound transmission loss properties of exterior building elements such as walls and windows. The OITC uses outside noise sources such as traffic, aircraft and trains to calculate a single number rating. The OITC is the preferred rating for exterior walls and roofs of metal buildings.

Conclusion

Noise is becoming an indoor environmental pollution issue as it can effect the health and performance of the building occupants. Construction techniques to reduce sound are becoming increasingly important and many builders and architects are looking for cost-effective ways to further reduce sound transmission in metal buildings. Adding faced metal building insulation alone to the metal building construction can reduce noise levels in a metal building by 5-6 dB. However, construction techniques do impact the way sound travels. To maximize a metal building’s acoustical performance, the wall and/or roof panels should include at least one layer of faced metal building insulation, and one layer of unfaced metal building insulation. Additionally, the construction should be tight, with attention to detail such as filling gaps with flexible sealants to assure that sound does not transit via air leaks from one space to another.