Wall noise or sound transmission control:
This article explains how to make sound-reducing or "soundproof" walls and partitions in buildings as a key component in noise control and sound privacy improvements. 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. This article discusses methods for controlling sound transmission through building walls.
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This article series discusses noise and sound control in buildings, and includes excerpts or adaptations from Best Practices Guide to Residential Construction, by Steven Bliss, courtesy of Wiley & Sons.
How effectively a wall or floor reduces airborne sound is measured by STC ratings (SOUND TRANSMISSION CLASS RATINGS). Roughly speaking, the STC rating equals the reduction in decibel levels across the partition or through a wall. Table 5-15 at left gives STC ratings for different partition wall designs.
Table of STC Ratings for Typical Wall Assemblies
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.
Recommended STC levels between bedrooms and adjacent rooms in single family homes and apartments are shown in our Table of Recommended Sound Control for Bedroom Partitions in Single-Family Dwellings.
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.
Table of STC Ratings for Typical Wall Assemblies (continued)
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