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Exterior Soundproofing That Works - Continued

Adding Mass

Normal wood-frame construction — 1/2-inch drywall, 3 1/2-inch studs and insulated cavity, and 5/8-inch sheathing with siding — does not create a noise path that requires treatment. However, uninsulated wall and ceiling framing may require treatment. A ceiling that is part of the roof assembly is exposed to more outside noise energy than a flat ceiling under an attic space. To absorb some of this energy, we increase the surface mass by applying an additional layer of 5/8-inch blue-board with a plaster skim coat, going directly over the existing layer of gypsum (Figure 7). Where attics exist above ceilings, no acoustical treatments are generally required as long as the ceiling has at least one layer of 1/2-inch gypsum board, and there is at least 9 inches of insulation in the joist bays.

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Figure 7. Applying the principle that surface mass absorbs noise energy, adding an extra 5/8-inch-thick layer of gypsum blueboard with a plaster skim coat helps to reduce the noise transmitted through flat-roof and cathedral-style ceilings.

Quiet room. Boston's Logan Airport program offers participating homeowners an extra measure of sound insulation beyond the typical door and window treatments. Homeowners may choose one room in their home to receive a "quiet room" treatment that effectively creates a room within the existing room. Any wall or ceiling in the designated room that has exterior noise exposure will have a second wall or ceiling constructed 1 inch inside of the existing surfaces (Figure 8). This, of course, results in some downsizing of the room's dimensions.

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Figure 8. Double wall and ceiling construction decouples, or isolates, the interior space from the exterior building envelope. Although the existing room size is slightly reduced, the thunder of a passing jet is lowered to background noise.

Surface isolation. Decoupling these rooms works very well — the thunder of a jet departing is reduced to background noise. The average tested noise rating of a quiet room is 45 dB — a 10 dB, or 50%, noise reduction beyond that achieved by our normal door and window treatments.

For these rooms to be optimally efficient, careful attention to detail is a must. We make sure that no elements bridge the gap between the new and existing walls and/or ceilings, and that seams and holes are tightly sealed. These are the steps:

• Set the new wall plate in acoustical sealant where it is in contact with the floor.

• Seal all electrical wall switches and receptacles with the same sealant.

• Use the standard elements of a normal 2x4 wood-framed wall in the double-wall construction, and include R-11 insulation (Figure 9).

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Figure 9. Double-wall 2x4 framing set in acoustical sealant caps the top and bottom of an existing boxed-out lower wall section. Fiberglass batt insulation absorbs sound energy. Resilient channel crosses 1x3 strapping over the existing ceiling, which is covered with semi-rigid acoustical fiberglass insulation, followed by a layer of 5/8-inch-thick blueboard with a plaster skim coat.

• Replace any windows in the existing wall with a new acoustical window.

• The double wall also receives an acoustical window, creating a double window construction (Figure 10).

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Figure 10. Even the windows get doubled in a sound-insulated room. Thermopane glass, minimum 2-inch air spaces between units, and a high-performance storm window present an effective barrier to external noise.

• To decouple the ceiling, install 3/4-inch-thick acoustical fiberglass insulation between wood strapping, directly over the existing ceiling.

• To reduce the transmission of vibration, cross the wood strapping with RC-1 resilient channel, and fasten a layer of 5/8-inch blueboard to it.

• A layer of skim-coat plaster and a prime coat of paint finish the job.

The only thing left for the homeowner to do is the final painting and decorating.

One of the main goals of the residential insulation programs is homeowner satisfaction and community goodwill toward the airports. As a testament to the adaptability of people, not to mention their savvy in not passing up a good deal, one program participant, when asked if she noticed the difference after her home was sound-insulated, responded, "I've lived here for 32 years, so I don't even think about the noise anymore, but I'm happy with the job —it looks very nice."

Michael Payne, AIA, is a principal and architect at the Jones Payne Group in Boston, Mass.

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