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This summary is not meant to take the place
of the full standard. The complete standard is available online
from the Acoustical Society of America: asastore.aip.org. The
text in italics is supplemental information provided by Acoustics.com
and is not a part of the actual standard.
Background Noise Levels
Background noise is comprised of noise from building systems, exterior
sound transmission, and sound transmission from adjacent spaces.
Excessive background noise can seriously degrade the ability to
communicate.
- For core learning spaces with internal volumes of 20,000 cubic
feet or less, one-hour steady-state background noise levels should
not exceed 35 dBA.
- For core learning spaces with internal volumes of 20,000 cubic
feet or more, one-hour steady-state background noise levels should
not exceed 40 dBA.
- If the noisiest
one-hour period during which learning activities take place is dominated
by transportation noise, the maximum noise limits are increased
by 5 dB.
Controlling the background noise levels within a space involves
careful consideration of several building systems. Noise from HVAC,
electrical fixtures, light fixtures, and plumbing systems should all
be considered in the noise control design. According to this standard,
it is the architect or designers responsibility to specify
systems and installation methods in order to meet the background noise
levels required in the standard. The implementation of the noise control
design is the responsibility of the contractor.
The standard goes on to list several minimum specifications for
HVAC systems including selection of grilles and diffusers, airflow
velocities, and duct lining. Light fixtures with low-noise ballasts
are recommended in learning spaces. Several suggestions are outlined
to limit noise from the plumbing system including, locate restrooms
away from classrooms, do not run piping above learning spaces, use
cast iron waste water pipes when possible, and resiliently isolate
all water piping from the structure. An important issue that is
mentioned in the standard is planning. One of the best ways to reduce
problems with background noise is to isolate quite areas, such as
classrooms, from noisier areas, such as mechanical equipment rooms.
Exterior sound transmission can also contribute to background noise.
In order to limit this concern, issues to consider in the design
of a new school include, site location, existing exterior noise
levels at the site, and prediction of future noise levels.
The background noise levels specified in this standard are very stringent.
In order to meet the specified levels, a designer will need to consider
background noise while in the design phase. Locate noisy areas away
from quieter areas. You will also need to work closely with the mechanical
engineer to specify an adequate HVAC system. A Noise Criteria of approximately
25-35 will be required. Also discuss sound control options with the
plumbing and electrical engineers.
Reverberation Time
Although some reverberation within a space can aide in speech distribution,
longer reverberation times will cause a build-up of noise and degrade
speech intelligibility.
- The maximum reverberation time for core learning spaces with
internal volumes of greater than 10,000 cubic feet should not
exceed 0.6 seconds.
- For core learning spaces with internal volumes of more than
10,000 but less than 20,000 cubic feet the maximum reverberation
time is 0.7 seconds.
- Reverberation
time for spaces with more than 20,000 cubic feet of internal volume
is not specified, however, guidelines are given in Annex C of the
standard.
The reverberation time within an existing space can be
tested with special equipment. Calculations can be done in order
to determine what the reverberation time will be in a proposed new
space. An explanation of the formulas and how they work can be found
in Annex C of the standard. Variables that affect the reverberation
time include the volume of the space and the amount of sound absorption
within the room. In order to determine the amount of sound absorption,
a material's absorption coefficient multiplied by the surface area
for that material must be calculated. Once the amount of absorption
for each material has been calculated, the sum of these will give
the total amount of sound absorption within the room. Laboratory-certified
sound absorption coefficients should be available from the manufacturer
of the material.
It is the designer or architect's responsibility to ensure that
a space meets the required reverberation times by providing the
appropriate amount of absorptive materials.
In order to achieve the required reverberation time, acoustical
treatments will be necessary on either the walls or the ceiling, or
most likely both. There are several options of acoustical treatments
available. If reverberation time is considered in the design phase,
the acoustical treatments can be a part of the design rather than
an unwanted addition. In order to determine the amount of absorptive
material necessary, the best locations for the materials, and different
material options, contact an acoustical consultant. An acoustical
consultant can assist you with all of the necessary calculations and
limit your liability.
Sound Transmission Class
The amount of airborne sound blocked from transmitting through a
partition is measured in a Sound Transmission Class (STC) rating.
A higher STC rating will Sound transmission through walls will add
to the background noise level in the space, degrading the ability
to hear and understand speech.
Single or composite walls, floor-ceiling and roof-ceiling assemblies
should provide specific sound transmission class (STC) ratings when
separating a core learning space from an adjacent space:
- STC-45 if the adjacent space is a corridor, staircase,
office or conference room,
- STC-50 if the adjacent space is another core learning
space, speech clinic, health care room or outdoors,
- STC-53 if the adjacent space is a restroom,
- STC-60 if the adjacent space is a music room, mechanical
equipment room, cafeteria, gymnasium or indoor swimming pool.
- Classroom doors should be rated as STC-30 or more, and
music room doors as STC-40 or more. Entry doors across
a corridor should be staggered to minimize noise transmission.
- STC ratings ranging from 45-60 are outlined for assemblies
separating ancillary spaces from adjacent spaces.
- (Note: Open-plan classroom designs will
not meet the requirements of this standard.)
Achieving a specific
STC rating depends highly on the materials and the installation
methods used. Wall and ceiling assemblies can be specified and detailed
to meet a required STC rating. This is the architect or designer's
responsibility. However, specifying an STC level is not all that
will be required. It is important to note that sound transmission
can be strongly affected by sound leakage through penetrations,
joints, and over or around the structure.
The number and location of penetrations through the wall, as well
as the number and location of electrical outlets should be considered
in the design. In order to meet a specified STC, installation methods
become crucial. Placement and installation instructions for the
electrical system are given within Annex B in order to limit sound
transfer between rooms. For single stud walls, electrical boxes
should not be located within the same stud space. For staggered
or Dual stud walls, boxes should be separated by at least 24". If
back-to-back electrical boxes cannot be avoided, they should be
enclosed in full gypsum board enclosures that do not contact the
framing of the other row of studs. Additionally, all joints and
air gaps should be sealed air tight with caulking or acoustical
sealant.
As mentioned previously, background noise is a major concern in
learning facilities. STC ratings will help to limit the background
noise levels within a space (depending on the effect of sound transmission
on the background noise level). It may be necessary to increase
a required STC rating in order to meet a specified background noise
level requirement.
Sound transmission problems can be avoided or lessened by good site
selection and good space planning.
Typical, single stud construction will not meet the required STC
ratings. The walls will most likely require staggered or dual stud
construction and/or multiple layers of drywall. (There are also specialty
products that can help ensure compliance.) It is also important to
note that acoustical ceiling tiles will not prevent sound transmission
over the wall. Walls surrounding core learning spaces should extend
to the deck of the building structure in order to adequately control
sound transmission.
Carefully consider the placement of electrical outlets. Do not place
them back-to-back. Again it will be important to work with your electrical
engineer in order to specify installation instructions that will limit
sound transmission. Specify on your drawings for contractors to seal
all joints and penetrations with an acoustical sealant.
Most importantly, do not locate mechanical equipment rooms, restrooms,
music rooms, gymnasiums, cafeterias, or any other noisy space adjacent
to a class room or core learning space.
Impact Insulation Class
Impact Insulation Class (IIC) is a rating for the ability of a floor-ceiling
assembly to block impact/structure borne noise from transmitting
to the space below. A floor-ceiling assembly with a low IIC rating
will potentially cause distracting noise in the room below, leading
to possible annoyance and problems with communication.
- IIC ratings
for floor-ceiling assemblies above core learning spaces should be
at least IIC-45 and preferably IIC-50 (measured without carpeting
on the floor).
- In new construction, gymnasia, dance studios or
other high floor impact activities shall not be located above core
learning spaces.
- In existing facilities IIC-65-70 (depending on
the volume of the space below) is recommended if gymnasia, dance
studios or other high floor impact activities are located above
core learning spaces.
IIC is a major concern for multi-story educational
facilities. The floor-ceiling system should be specified and constructed
in order to meet the specified IIC rating. Installing carpet on
the floor above will help reduce impact sounds. It may be necessary
to isolate the finished floor from the structural floor or to isolate
the ceiling from the floor above. For any vibrating machinery located
on the floor above or on the roof structure, rubber pads or spring
systems should be installed. As with all requirements in the standard,
it is the architect or designers responsibility to make the necessary
steps in specification and design, but careful construction and
installation will be necessary to ensure compliance.
This is only a concern for multi-story schools. In most cases,
installing carpet on the floor above will dramatically improve the
IIC rating. In order to achieve the specified levels, a separate hard
lid ceiling assembly could be required. Ideally, this would be completely
isolated from the floor structure above. The classroom below may still
need an acoustically absorptive ceiling treatment in order to meet
the required reverberation time. Working with your mechanical engineer,
be sure to specify appropriate vibration dampening measures for mechanical
equipment.
Verify Conformance
Annex E of the standard goes on to outline architectural practices
and procedures to verify conformance with the standard. Steps include,
design to conform, monitor activities during construction, check
for conformance before completion of construction is accepted.
Testing is not required by the standard but should be done in order
to verify conformance. An acoustical consultant can test background
noise levels, reverberation time, STC and IIC using special testing
equipment. The standard itself gives conformance tolerances in each
area.
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