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Photograph of sound and noise control measures for buildings.Guide to Sound Control in buildings: Sound Transmission

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Building Noise & Sound Control:

Sound insulation designs for building walls. Sound control for building floors. How to control plumbing noises & sounds. List of soundproofing materials. Tables of sound control data for buildings.

This article series presents methods and materials used to control sound transmission in buildings: how to make a quiet home, office, or place of business using sound isolation for ceilings, floors, walls, plumbing, etc.

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Quiet Please! Best Practices Guide to Sound Control in buildings

Table of typical sound levels in decibels dB (C) J Wiley & Sons Best Practices Steven BlissThis 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.

[Click to enlarge any table or illustration]

The page top illustration from the above text shows an example of a design to reduce transmission between building floors.

Because of its stiffness, wood framing (photo at left) readily transmits low-frequency sounds and impact noises through wood- frame houses. This is particularly a problem in floors and walls separating two housing units, but it can also be an issue within a single-family home.

For example, a person with a home office or music room might want to isolate it acoustically from the surrounding rooms so meetings or music proceed in private and so outside noises will not intrude.

Bedrooms located under living spaces can also require special treatment to reduce impact noises from above.

Another kind of noise control is important where a house sits by a highway or under a flight path.

The goal here is to keep outdoor noises from entering the house by reducing sound transmission through windows, doors, and exterior walls and ceilings. Special acoustical windows rated for low sound transmission are often required for substantial reductions in outside noise.

Principles of Sound Transmission

Sound can travel through both air (airborne sound) and solid materials (structure-borne sound). Structure-borne sound can be directly imparted to the building structure by a vibration, such as a humming compressor, or by direct impact, such as a boot stepping on a hardwood floor.

As sound energy travels through a building, it changes from one type of transmission to the other and back, losing energy in each transition. Because of its rigidity, wood framing is a very good transmitter of low-frequency sound and hollow wall cavities and thin doors do little to reduce sound transmission.

How Sound Levels are Measured in buildings - What is a Decibel

Sound levels are measured in decibels (dB), which are on a logarithmic scale. A sound increase of just 10 dB indicates an increase of ten times the intensity, although our subjective experience is that the sound is twice as loud.

Decibel levels for common sounds are shown in Table 5-14 above on this page.

Continuous exposure to sounds above about 85 dB can cause hearing loss in most people.

See also DECIBEL METER dB METER CHOICES

Sound Absorption vs. Sound Isolation in buildings

Sounds in an acoustically “live” room with all hard surfaces will seem loud and harsh due to the sound reverberating off the hard surfaces.

Adding sound-absorptive materials, such as carpeting and soft furniture, will make sound softer and more pleasant within the room, but will do little to reduce the transmission of sound to adjacent rooms.

To reduce transmission requires sound isolation strategies, typically using high- mass materials, double-framed walls, or resilient connections between the drywall and framing.

Sound Isolation Strategies for Indoor Noise Reduction

To keep airborne sound from passing through walls and floors, there are four main strategies:

A cavity with fiberglass is far more effective at blocking sound if the two wall surfaces (or ceiling and floor surfaces) are mechanically decoupled as in a double-stud or staggered-stud wall. Resilient channel works essentially the same way by breaking the vibration path from the stud or ceiling joist to the drywall.

The hardest sounds to block are low frequency, such as the thumping of a stereo bass. Using decoupled construction, such as double walls or resilient channels, is effective.

Where that is impractical, adding mass can also be effective. Very massive, non rigid materials such as lead or sand are ideal, but doubling or tripling the drywall is also helpful.

Wall Upgrades for Sound & Noise Transmission Control

In single-stud walls, the most cost-effective upgrade is to double the drywall on one side and add insulation to the cavity, increasing the STC from 33 to 40.

See Table 5-16 just below.

Table of sound transmission control factors (C) Steven Bliss J Wiley Inspectapedia.com

[Click to enlarge any table or image]

The joints on the second layer of drywall should not line up with the first layer.

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 higher STC 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.

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 even higher ratings, which might be needed for a music room, for example, double doors are required. See Table 5-17 below: Sound Transmission of Interior Doors.

Table 5-17 below: Sound Transmission of Interior Doors. (C) InspectApedia.com Steven Bliss J Wiley

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 below.

Table 5-18 Recommended Sound Control for Bedroom Partitions (C) InspectApedia.com Steven Bliss J Wiley & Sons.

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.

Sound Transmission Through Floors

The STC rating of a floor measures only the Reduction in airborne sound transmission. A floor, however, also transmits structure-borne sound, such as footsteps or a slammed door, directly through the materials. The ability to reduce impact sound is rated by the Impact Isolation Class (IIC) rating.

The most cost-effective technique to reduce impact noise is to add a carpet and pad. For example, adding a carpet and pad to a conventional plywood subfloor over a gypsum ceiling increases the IIC rating from 37 to 65. By comparison, it increases the STC rating by only 4 points.

Where higher STC and IIC ratings are needed, a resilient channel can be added to the ceiling below. Where this is not possible, for example when the joists are exposed below, you can use a floating floor over a layer of soundboard or a high-mass floor over a layer of sand or lightweight concrete (see Table 5-19).

Table of STC & IIC Ratings for Typical Wall / Ceiling Assemblies (C) Steven Bliss J Wiley InspectApedia.com

[Click to enlarge table]

IIC levels are of greatest concern in stacked multifamily dwellings or in a single-family dwelling with bedrooms below other living spaces. Acoustical experts recommend a minimum IIC rating of 50 to 55 in ceiling/floor construction, separating living units in multifamily construction.

HUD recommendations for bedrooms under living spaces are shown in Table 5-20. While these recommendations were developed for multifamily dwellings, they provide reasonable targets for single-family homes where sound privacy is desired.

Table 5-20 Minimum Sound Insulation for Ceiling / Floor Assemblies above bedrooms (C) J Wiley Steven Bliss InspectApedia.com

Plumbing Noise & Sound Transmission Sources & Control

One of the most common noise complaints in single-family construction is the sound of water gushing through PVC waste pipes. The best solution, short of using cast iron, is to box in the pipes and fill the cavity with fiberglass insulation. Then enclose the cavity with one or two layers of drywall.

Water supply and heating pipes can also radiate noise through the framing if there is rigid contact between pipes and framing or finish materials. This can be a particular problem when heating pipes expand and contract. To avoid these problems, make sure pipe runs are not tight against framing.

Soundproofing Materials and Workmanship Like weatherization work, effective soundproofing requires careful detailing and workmanship. Small holes and bypasses can lower field STC values to 15 to 20 points below laboratory values.

Leaky edge joints, unsealed doorways, interconnecting ductwork, and unsealed electrical and plumbing penetrations all degrade acoustical performance.

How to Use Acoustical Sealant for Sound Control

While special non hardening acoustical sealants are often specified in commercial work, any high-quality sealant that remains flexible can be effective in blocking sound transmission. Butyl, silicone, and urethane caulk can all be used.

To prevent sound leaks, use sealant around electrical boxes, plumbing penetrations, and any other penetrations in the wall or ceiling surface. For walls with STC ratings in excess of 35, apply a flexible sealant at the joint where the drywall meets the floor. Acoustical sealant is also used to seal around the perimeter of walls or ceilings hung from resilient channel.

How to Use Resilient Channel for Noise Control

Resilient channel is installed perpendicular to the studs or joists and needs at least 3 inches of free space in the cavity behind it to be effective. It is not effective if attached to sheet materials, such as drywall. It is also important to use the right length screws, so they do not penetrate into the wood framing.

Just a few screws into the wood can undermine the resilient connection and substantially lower the STC and IIC ratings. Leave a 1/4-to 1/2-inch gap around the perimeter of a ceiling or wall hung from resilient channel and fill with an acoustical or other non hardening sealant.

How to Use Insulation to Control Noise Transmission in buildings

Ordinary fiberglass insulation is an effective sound absorber in cavities and increases the STC rating of walls by 3 to 5 decibels. The insulation needs to fill only about three-quarters of the thickness of the cavity to be effective.

Adding more adds little additional sound protection, and stuffing insulation in too densely could actually increase sound transmission. Cellulose insulation has about the same sound deadening characteristics as fiberglass.

Foam insulation is not particularly effective for sound control. Foam is too light to add mass to the wall and is not resilient enough to absorb sound.

Guide to Using Gasketing for Sound Control

Flexible, heavy rubber gasketing makes an effective seal against sound leaks as well as thermal leaks around doors and windows. Either bulb- or magnetic-type weather-stripping is effective as long as it makes an airtight seal between the frame and door or window.

Duct Insulation.

Use fiberglass ductboard or fiberglass duct liners to quiet the noises of fans and moving air. Avoid sharing a common duct between two rooms that need sound privacy.

-- Adapted with permission from Best Practices Guide to Residential Construction.

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