Sound Transmission Class (STC)
Definition
STC is expressed in decibels (dB) and is used to measure
a building material's ability to reduce sound. A higher STC rating translates
into more reduction in sound. Laboratory testing is used to measure the
resistance of partitions such as walls, windows, or doors to the passage
of sound.
The material with the lowest resistance to the passage of sound limits a partition's STC value. Poor construction practices can also nullify a partition's sound reduction properties. Cracks due to improperly fitted doors or windows can be a prime source of sound leakage.
HUD Criteria and Standards
The Department of Housing and Urban Development (HUD) has
developed criteria and guidelines for determining project acceptability
and necessary mitigating measures to achieve the goal of a suitable living
environment. It is HUD's policy to provide minimum national standards on
HUD programs (new construction and modernization) to protect citizens against
excessive noise in their places of residence.
HUD defines the external noise environment in terms of a day-night average sound level (DNL) expressed in decibels. Site acceptability standards and noise reduction measures are based on the DNL in a prescribed location.
| DNL | Site Acceptability | Special Approvals & Requirements |
| « 65 dB | acceptable | none required |
| »65 dB and «75 dB | normally unacceptable | special approval & sound reduction needed (1) |
| above 75 dB | unacceptable | special approval & sound reduction needed |
It is a HUD goal that the interior environment shall not exceed a DNL of 45 decibels. Design and construction techniques that reduce sound, in addition to measures that reduce external noise, are used to meet sound reduction requirements. HUD requires a noise assessment for proposed new construction if the project is located within 5 miles from a civil airport, 15 miles from a military airport, 1000 feet from a highway/busy road, or 3000 feet from a railroad.
STC Values
ODL conducted third party lab testing on a range of 22x64
doorglass configurations. STC is independent of doorglass size. Test results and benchmark values are presented below.
| Configuration | STC | Comment |
| Decorative glass with caming | 31 | Third party tested |
| Secure by Design decorative laminated glass | 38 | Third party tested |
| 1" IG clear glass, 3/4" air space | 31 | Third party tested |
| 1/2" IG clear glass, 1/4" air space | 28 | Third party tested |
| Severe Weather® Doorglass | 36 | Third party tested |
| Internal Muntin Doorglass Blind | 35 | Third party tested |
| 3x7' steel door, 1 3/4" thick with polyurethane core |
26 | from HUD Noise Notebook (2) |
| 30x48" alum. clad casement window, 1" IG with 1/8" panels |
29 | from HUD Noise Notebook (2) |
(1) Requires a minimum of 5 decibels in additional sound reduction on
buildings with noise sensitive uses if DNL »65dB and «70dB.
10dB in additional sound relief is required if DNL» 70dB and « 75dB.
(2) Source: HUD Noise Notebook Chapter 4 Supplement, Sound
Transmission Class Guidance
