330
Partitions: Acoustics
335
335.1
PARTITIONS
The need for resistance to airborne sound transmission through partitions
varies between STC 35 and STC 50. (See Section 510 and 520.) The
requirement for STC 55 between mechanical spaces and patient rooms is
typically provided by a concrete wall which separates the service bay from
the rest of the service module.
The STC of the partitions can be varied by the number and thickness of
layers of gypsum board and the inclusion or omission of sound attenuation
blankets. (See Figures 330-4 and 330-5.)
Laboratory ratings for sound isolation in general are consistently higher
than the performance found in actual field installations. Factors which
contribute to poor field performance include "flanking" transmission paths
through and around the partition (namely through joints and penetrations,
inadequate ceiling and perimeter detailing, etc.) and poor workmanship.
Proper construction details at the perimeter of the partitions and close field
supervision are extremely important.
All openings and construction joints should be well caulked and sealed
airtight, and there should be no penetrations through the partitions. Any
gap or hole quickly deteriorates the performance of a partition. This can
be shown by the following example:
For a partition having a sound attenuation value of 40 decibels, a .1%
opening, i.e., a .04 inch crack around a 3' x 7' door in an 8' x 10' wall, will
result in that partition having a net attenuation of 30 decibels. For
partitions having greater sound isolation, the same size opening will have
a greater effect in reducing its isolating characteristic.
335.2
DOORS
Where sound isolation is critical, doors should be selected having sound
isolation ratings equivalent to the partitions in which they occur. A 3' x 7'
door with STC 30 placed in an 8' x 10' wall with STC 50 would result in a
composite rating of approximately STC 36. The cost premium for doors
with acoustic ratings above STC 25-30 is significant, however, so the
benefit of their use should be carefully weighed.
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