Wall Noise & Sound Control - Sound Transmission Through Building Walls InspectAPedia® -
What is the definition of STC Sound Transmission Class?
Table of Sound Transmission Class Ratings - (STC ratings) for various building wall & floor designs
Sound transmission control design details for building walls and partitions
Questions & answers about noise & sound transmission through building walls - sound transmission pathways and how to control noise or sound in buildings
This article discusses methods for controlling sound transmission through building walls. Here we define STC - sound transmission class and we provide a table of design details that show STC rating for various building wall framing designs. Sound transmission reduction wall designs are given for both single stud and staggered double stud structural and partition walls. We include soundproofing suggestions for high noise level areas such as music rooms as well as areas where privacy is a concern such as in counseling and psychotherapy offices.
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Our building sound control articles begin at SOUND CONTROL in buildings. Other noise and sound diagnosis and control articles are found at NOISE / SOUND DIAGNOSIS & CURE. The page top table from the above text shows sound transmission class ratings mapped against typical sound levels in buildings.
How effectively a wall or floor reduces
airborne sound is measured by STC ratings (sound transmission
class). Roughly speaking, the STC rating equals
the reduction in decibel levels across the partition. (see Table 5-15).
So, for example, a 50 dB noise on the other side of an STC 35 wall
will sound like a 15 dB noise to the average listener (see our
Table of STC ratings and noise reduction left).
Walls and floors in the field often measure
lower than in laboratory ratings due to variations in workmanship
as well as leaks and bypasses.
The higher the STC
rating, the more likely it is to be compromised by site
conditions. For that reason, it is best to select a building
assembly rated at least 5 points above the design goal.
Sound Control Design & Materials for Sound Transmission Through Building Walls
Sound transmission reduction In single-stud walls, the most cost-effective sound control upgrade is to
double the drywall on one side and add insulation to the
cavity, increasing the sound transmission class (STC) from 33 to 40 (see Table of STC ratings of typical wall assemblies at left - click to enlarge the table).
The joints on the second layer of drywall should not line
up with the first layer.
Double-framed soundproof wall construction details: To achieve substantially higher STC ratings requires
adding a resilient channel to one side of the wall or decoupling
the two sides of a wall with double framing.
With no
rigid connection bridging the two sides of the wall, sound
transmission is significantly reduced.
Decoupling and also
increasing mass, such as doubling the drywall layers, will
help cut transmission of low-frequency sounds as well.
For party walls between adjacent living units, STC
ratings should be a minimum of 50.
Where privacy and quiet are of concern to clients, a minimum
STC rating of 45 is a reasonable target for bedroom
and bathroom partitions.
For higher STC wall sound transmission values required for special situations,
such as a music room or home office, additional upgrades
include increasing the mass on either side of the cavity,
enlarging the cavity, or adding fiberglass batts or other
sound-absorbing materials.
Filling the gap more than three quarters
of its width with insulation provides little additional
benefit. In fact, stuffing the cavity too tightly could reduce
the benefit of the fibrous insulation by creating a solid
bridge. In general, polystyrene and other closed-cell insulations
are poor sound absorbers and provide little benefit.
Closets along a wall can help
buffer sounds as long as doors are solid, not louvered.
In general, doors should be within 10 STC points of
the surrounding wall. Solid-core doors are recommended
for bedrooms and bathrooms. Where higher-level sound
isolation is required, you will need to add high-quality
gasket-type weather-stripping and a sealed threshold. Also
the gap between the door jamb and studs should be
caulked or grouted to avoid sound leaks around the door.
For party walls between adjacent living units, STC
ratings should be a minimum of 50. Recommended STC
levels between bedrooms and adjacent rooms in single family
homes and apartments are shown in Table 5-18.
Where privacy and quiet are of concern to clients, a minimum
STC rating of 45 is a reasonable target for bedroom
and bathroom partitions. Closets along a wall can help
buffer sounds as long as doors are not louvered.
Continue reading about methods for sound control in buildings by using the links provided just below.
Questions & Answers regarding this article
Questions & answers about noise & sound transmission through building walls - sound transmission pathways and how to control noise or sound in buildings
Steven Bliss served as editorial director and co-publisher of The Journal of Light Construction for 16 years and previously as building technology editor for Progressive Builder and Solar Age magazines. He worked in the building trades as a carpenter and design/build contractor for more than ten years and holds a masters degree from the Harvard Graduate School of Education.
Excerpts from his recent book, Best Practices Guide to Residential Construction, Wiley (November 18, 2005) ISBN-10: 0471648361, ISBN-13: 978-0471648369, appear throughout this website, with permission and courtesy of Wiley & Sons. Best Practices Guide is available from the publisher, J. Wiley & Sons, and also at Amazon.com.
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