MIL-HDBK-1191
23.2.2.4
Doors. Doors (and windows) are usually limiting elements in the
sound isolation of a construction system. Typically, since corridors are not
used as waiting (or otherwise normally occupied) spaces, the overall STC
rating of the corridor door/framing system is not critical. However solid
door (leaf) meeting the STC class requirement in Appendix A, shall be
provided. Special applications may require very limited undercuts, or
possibly gasketing. When a door occurs in a partition separating noise
critical spaces, special attention should be given to minimizing the undercut
and or gasketing. In other words, in rooms for which full isolation is
required, the door should provide the same corresponding degree of sound
isolation as the walls, floor and ceiling.
23.2.2.5
Windows. Windows, as doors, are also limiting elements in the
sound isolation of a construction system. In the same manner, windows
normally are not a major factor unless they are part of a wall construction,
which is between two spaces requiring sound isolation. In this case, the
medical facility designer shall evaluate the effectiveness of the composite
construction (window and wall); see section 23.2.3. In special cases,
attention must be given to providing sound limiting window constructions to
eliminate outside noise sources. In this case the medical facility designer
shall evaluate alternative solutions. In addition, designers shall coordinate
with the security considerations in other sections of this document.
23.2.2.6
Operable partitions. The sound isolation provided by operable
partitions depends to a great extent upon the effectiveness of the perimeter
seals. A good seal is difficult to maintain at the perimeter of these
partitions, and the actual sound isolation provided often falls far below
laboratory test ratings. From an acoustical standpoint, operable partitions
should be avoided where possible.
23.2.3
Composite Construction.
23.2.3.1
General. Composite constructions commonly occur in health care
facilities where the intervening construction systems contain doors, windows,
and suspended ceilings that have different STC ratings. To achieve the
required degree of sound isolation and speech privacy between the spaces, the
weighted contribution of each construction element in the system should not be
significantly lower than any other. The elements shall be weighted by their
STC value and the percent of the total wall area involved. To achieve
balanced contribution of sound energy through each element of a composite
construction, use the following approximation, based on the relative size of
each element.
Area of element relative to
Allowable NR (or STC) of
total area of wall
element relative to NR (or
STC) of wall (dB)
less than 25%
-5 to 7
25% to 50%
-2 to 3
greater or equal to 50%
0
For example, to maintain balanced construction, a door in a partition can have
a Noise Reduction (or STC) of 5 dB to 7 dB less than the wall, if the size of
the door is smaller than 25% of the size of the wall. If the NR (or STC) of
the wall is 40, the NR (or STC) of the interconnecting door should be 33 to
35.
23.2.3.2
Detailed calculation. If the above general guidelines and
relationships are inadequate for a pertinent analysis, then use Figure 23.4.
for more accuracy. As an example, consider the situation of a partition with
a door in it, as in the following computations:
23-4
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