FAQ Category: Specialty Doors

OITC stands for Outdoor-Indoor Transmission Class and is a measure of the ability of a building material or product’s ability to retard sound transmission. It is similar to STC, but it is not the same. As the name indicates, OITC is a measure of sound transmission from the external environment into the building envelope. Testing to establish an OITC value utilizes ASTM E-1332 Standard Classification for the Determination of Outdoor–Indoor Transmission Class. This standard uses a range of frequencies lower than the STC testing, to more closely replicate the sounds of rail and vehicular traffic.

STC stands for “Sound Transmission Class”, a measure of the extent to which sound is prevented from being transferred from one area to another. The higher the STC value, the less sound transferred from one area to another.

The STC scale is a logarithmic progression, meaning that a jump of 3 points in an STC rating equates to a doubling in a door’s ability to prevent sound transmission. Acoustical doors are tested as an assembly comprised of the door, frame, hinges, and sound sealing system. See SDI 128 for more information.

The following chart illustrates the sound retardant performance associated with a range of STC values.

Most manufacturers conduct acoustic tests with grout filled frames to optimize the lab performance. Acoustic performance will be reduced on frames over STC 40 when grout or sound retarding material is eliminated.

TC is a single number rating that indicates the sound transmission loss over a defined range of frequencies of a door assembly between adjacent closed rooms. Higher values equate to better sound reduction performance.

Decibels dB, are used to express the intensity of a sound wave. Examples of decibels levels are:

• 100-120 Deafening industrial machinery, jet engines
• 80-100 Very loud cocktail party, boom box
• 60-80 Quiet speech
• 20-40 Faint soft whisper, recording studio
• 0-20 Very faint acoustical laboratories, deep caves

STC ratings would be specific to each manufacturer and design, typical higher range ratings are between 50 and 55.

STC rated doors are generally supplied with a label that is either Mylar or metal, but the products are not listed like fire doors by agencies such as Underwriters Laboratories or Warnock Hersey. Labels are for manufacturer and rating identification purposes only.

Typically, doors with higher STC ratings have increased cost, weight and lead time.