Masonry Magazine April 1970 Page. 17
Table 2 Sound Transmission Class Limitations
| Location of Partition | Low Background Noise Bedroom adjacent to partition | Other rooms adjacent to partition | High Background Noise Bedroom adjacent to partition | Other rooms adjacent to partition |
|---|---|---|---|---|
| Living Unit to Living Unit | 50 | 45 | 45 | 40 |
| Living Unit to corridor | 45 | 40 | 40 | 40 |
| Living Unit to Public Space (Average Noise) | 50 | 50 | 45 | 45 |
| Living Unit to Public Space & Service Areas (High Noise) | 55 | 55 | 50 | 50 |
| Bedrooms to other rooms within same living unit | 45 | NA | 40 | NA |
SELECTION OF WALLS
After the STC requirements for the various walls and partitions of multifamily housing have been determined, the corresponding type and thickness should be selected on the basis of structural and acoustical considerations. Minimum structural adequacy will not necessarily assure minimum acoustical adequacy. In choosing the type of concrete masonry for walls and partitions, evaluation of the porosity and density of the material should be a factor for consideration. Resistance to sound transmission increases with unit weight and decreases with porosity. Unpainted, open textured units will display improved resistance to sound passage after surface sealing from application of plaster or paint. At the same time, sealing of the pores results in a corresponding reduction in the sound absorption capability of the block. The approximate STC of concrete masonry walls and partitions corresponding to wall density, are shown in Fig. 2.
Because of some confusion between sound absorption and sound transmission, an erroneous conclusion has sometimes been reached that by using open textured concrete block, both sound absorption and sound insulation could simultaneously be obtained. The objective is generally not completely achievable. There are instances, however, in which the designer may wish to use both properties of concrete block to advantage. In multifamily housing the designer can consider using concrete masonry partitions to separate public areas such as stairwells and corridors from adjacent living areas. In this application the open textured surface of the concrete block is left unpainted or given a thin coat of paint to retain sound absorption for the reduction of echo effect from corridor sounds. Sound transmission reduction is achieved through plastering the surface of the living area on the opposite side of the partition. A similar technique which affords sound absorption on both sides of the wall as well as sound reduction, uses open textured units in a cavity wall with back plastering on the inside face of one of the wythes.
Table 3 Background Noise Levels and Privacy Requirements
| Area | Background Noise Level (db) | Privacy Desired | Minimum STC Required |
|---|---|---|---|
| Rural | 20 | High | 60 |
| | | Medium | 50 |
| | | Low | 45 |
| Suburban | 30 | High | 55 |
| | | Medium | 45 |
| | | Low | 40 |
| Urban | 40 | High | 45 |
| | | Medium | 40 |
| | | Low | 35 |
FIG. 2 STC VS. WALL WEIGHT FOR SINGLE-WYTHE PAINTED OR PLASTERED BLOCK WALLS