Stewart Acoustical Consultants of Raleigh NC conducted tests according to ASTM standards E413 and E1322 to develop apparent Field Sound Transmission Class (FSTC) and Field Outdoor-Indoor Class (FOITC) ratings for the exterior walls of the buildings at the Hughes evaluation site.
Results of the sound tests suggest that while wall sound attenuation qualities of these assemblies do vary, sound flanking through doors, windows, gable ends, and under floor assemblies in crawl spaces, negates some of the sound dampening benefit of the laboratory developed ratings of these walls. For example, apparent FSTC ratings developed for the building end walls, which are void of openings, ranged from 39 to 46. The same methodology and equipment resulted in apparent FSTC ratings of 30 to 32 for the front walls, which are penetrated by three openings that account for 25% of the buildings' front wall surface.
Good design features, like the back-to-back closets at the duplex common walls and separation of wall assemblies like the three and-one half-inch-thick brick veneer with three quarter-inch drainage plane that clad each of the buildings, are probably as important to sound attenuation performance in typical one- and two-family homes.
NAHB Research Center