Sound Control in Buildings - Cut off Flanking Sound Paths InspectAPedia® -
What are flanking pathways for sound leakage in buildings
How do we cut off flanking paths for sound
Design details for soundproof doors and doorways
Use of sound sealants for partition walls
Controlling transmission of bathroom noises in buildings
How to make a building quiet: sound isolation strategies
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This article explains how sound flanking paths, sound leaks around and through building components, defeats incomplete attempts to reduce building sound transmission and noise levels. We include design details for sound reducing details in buildings including soundproof office doorways and doors. This article includes excerpts or adaptations from Best Practices Guide to Residential Construction, by Steven Bliss, courtesy of Wiley & Sons.
The page top photograph shows a pair of solid core doors installed at the entry to an office where sound transmission and privacy are a concern. Below we provide more details about soundproofing at doorways.
Sound takes the path of least resistance
between rooms, through any air leaks or through rigid
connections in the structure itself. These routes that bypass
efforts at sound insulation are called flanking paths.
These can significantly reduce the effectiveness of soundproofing
efforts. Building walls with high STC ratings will
do little good if sound can pass easily though electrical
outlets or a thin, loosely fitting door.
For example, an ungasketed
door or the equivalent of a one-inch-square hole
in a wall can reduce an STC 50 wall to STC 30. Common
flanking paths include:
Air leakage around partitions; around doors; and through
plumbing penetrations, back-to-back medicine cabinets,
unsealed electrical outlets or recessed lights (Figure at left).
Shared ductwork between two rooms.
Hollow-core doors and single-pane glass, which are
good sound transmitters.
With resilient channels, a few drywall screws that
penetrate into the ceiling joists, undermining the
decoupling system.
With decoupled framing, a solid path through a band
joist or drywall panel that provides a bypass for
structure-borne sound.
Minimizing sound noise transmission flanking paths requires both good planning
and workmanship. Common strategies to control flanking path for noise in buildings include:
Avoid back-to-back holes for electrical and mechanical
equipment.
Partition wall sealants: Along partition bottoms, leave a 1/4-inch gap between the
drywall and subfloor, and fill with acoustical sealant.
Bathroom noises: On bathroom partitions, install drywall all the way to
the floor before installing the tub and seal all plumbing
penetrations through walls with a flexible sealant.
Design Details for Soundproof Doors & Doorways
Soundproof doorways: Upgrade to solid-core doors and add weather-stripping. Our photo (left) shows an installation of doubled solid core doors that has been found effective in minimizing sound transmission between a counseling office and its waiting room. Similar to the double sound-transmission resistant doorway shown at the top of this page, here the designer incorporated a short hallway between a waiting room and the counseling office. Outside a waiting room closet, forming one wall of the entry hall, provides additional soundproofing and privacy for this space. As we discuss below at Sound Control for Walls, closets provide additional sound transmission buffering provided their doors are solid, not louvered.
Addressing obvious flanking paths is often the most cost-
effective step in soundproofing a home. Strategies such as
sealing air leaks between rooms, upgrading doors, and adding
weather-stripping may provide adequate sound isolation
without the need for more exotic and expensive measures.
In general, sound-resistant doors should be within 10 Sound Transmission Class (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. A doubled sound transmission resistant interior door installation is shown at Cut Off Flanking Sound Paths.
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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