Legal and Practical Requirements
Section 1207 of International Building Code 2006 states that separation between dwelling units and between dwelling units and public and service areas must achieve STC 50 (STC 45 if field tested) for both airborne and structure-borne. However, not all jurisdictions use the IBC 2006 for their building or municipal code. In jurisdictions where IBC 2006 is used, this requirement may not apply to all dwelling units. For example, a building conversion may not need to meet this rating for all walls.
In serious cases (e.g., a bedroom adjacent to a home theater room, and an inconsiderate nocturnal neighbor, to boot) a partition to reduce sounds from high-powered home theater or stereo should ideally be STC 70 or greater, and show good attenuation at low frequencies. An STC 70 wall can require detailed design and construction and can be easily compromised by 'flanking noise', sound traveling around the partition through the contiguous frame of the structure, thus reducing the STC significantly. STC 65 to 70 walls are often designed into luxury multifamily units, dedicated home theaters, and high end hotels.
Sound Transmission Class (or STC) is an integer rating of how well a building partition attenuates airborne sound. In the USA, it is widely used to rate interior partitions, ceilings/floors, doors, windows and exterior wall configurations (see ASTM International Classification E413 and E90). Outside the USA, the Sound Reduction Index (SRI) ISO standard is used.
| STC | What can be heard |
|---|---|
| 25 | Normal speech can be understood quite easily and distinctly through wall |
| 30 | Loud speech can be understood fairly well, normal speech heard but not understood |
| 35 | Loud speech audible but not intelligible |
| 40 | Onset of "privacy" |
| 42 | Loud speech audible as a murmur |
| 45 | Loud speech not audible; 90% of statistical population not annoyed |
| 50 | Very loud sounds such as musical instruments or a stereo can be faintly heard; 99% of population not annoyed. |
| 60+ | Superior soundproofing; most sounds inaudible |
| STC | Partition type |
|---|---|
| 33 | Single layer of 1/2″ drywall on each side, wood studs, no insulation (typical interior wall) |
| 39 | Single layer of 1/2″ drywall on each side, wood studs, fiberglass insulation |
| 44 | 4″ Hollow CMU (Concrete Masonry Unit) |
| 45 | Roxul Safe'n'Sound Insulation installed between wood 2 × 4 studs on 16″ centers and 5/8″ drywall (type x ) on each side with resilient channels at 16″ on one side |
| 45 | Double layer of 1/2″ drywall on each side, wood studs, batt insulation in wall |
| 46 | Single layer of 1/2″ drywall, glued to 6″ lightweight concrete block wall, painted both sides |
| 46 | 6″ Hollow CMU (Concrete Masonry Unit) |
| 48 | 8″ Hollow CMU (Concrete Masonry Unit) |
| 50 | 10″ Hollow CMU (Concrete Masonry Unit) |
| 52 | 8″ Hollow CMU (Concrete Masonry Unit) with 2″ Z-Bars and 1/2″ Drywall on each side |
| 52 | Roxul Safe'n'Sound Insulation installed between steel 2 x 4 studs on 24″ centers and 5/8″ drywall (type x) on each side |
| 54 | Single layer of 1/2″ drywall, glued to 8″ dense concrete block wall, painted both sides |
| 54 | 8″ Hollow CMU (Concrete Masonry Unit) with 1 1/2″ Wood Furring, 1 1/2″ Fiberglass Insulation and 1/2″ Drywall on each side |
| 55 | Double layer of 1/2″ drywall on each side, on staggered wood stud wall, batt insulation in wall |
| 59 | Double layer of 1/2″ drywall on each side, on wood stud wall, resilient channels on one side, batt insulation |
| 63 | Double layer of 1/2″ drywall on each side, on double wood/metal stud walls (spaced 1″ apart), double batt insulation |
| 64 | 8″ Hollow CMU (Concrete Masonry Unit) with 3″ Steel Studs, Fiberglass Insulation and 1/2″ Drywall on each side |
| 72 | 8″ concrete block wall, painted, with 1/2″ drywall on independent steel stud walls, each side, insulation in cavities |
STC partition ratings taken from: "Noise Control in Buildings: A Practical Guide for Architects and Engineers"; Cyril M. Harris, 1994
Read more about this topic: Sound Transmission Class
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