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Exterior Soundproofing That Works - Continued

Sliding patio doors. In the case of a sliding glass door, conditions occasionally dictate installing the sliding storm panel on the interior side of the prime door to provide adequate sill support (Figure 3). Since sliding-door handles project out from the face of the door and may interfere with one another, the space between the doors may have to be greater than 2 inches.

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Figure 3. Sliding storm panels provide extra sound insulation at sliding door locations. In every instance of a secondary door or window, there should be a minimum 2-inch gap between primary and storm units.

Gasketing. It is acoustically important that both prime and storm doors are well-gasketed with continuous weatherstripping to minimize air leakage. The weatherstripping should create a flexible, shape-conforming, airtight seal between door and frame. We use polyprene or polypropylene bulb weatherstripping because they maintain flexibility longer than other types of weatherstripping without stiffening or cracking.

With the correct airtight seal, you can feel a vacuum-type resistance when you open the primary door with the storm door closed, and a compressive pressure when you close it again. Weatherstripping at the threshold, preferably with a flip-down sweep, is equally important (Figure 4).

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Figure 4. An automatic door sweep ensures a good seal against air and noise infiltration at the threshold.

Air Quality

In the process of replacing all of the windows and doors and sealing other points of airflow, a home's exterior envelope becomes considerably tighter than it was before. As a consequence, indoor air quality may suffer and combustion devices may become oxygen-starved. Older homes without vapor barriers and modern insulation usually continue to breathe sufficiently; with newer homes, however, we specify additional ventilation to provide make-up air for the health of the occupants and normal operation of the home's mechanical systems.

Installation Guidelines

Whatever type of windows or doors are used, proper installation is critical to acoustical performance. The principle of tightness is the controlling guideline to ensure that the acoustical performance is not degraded by flanking path leaks around the perimeter of the installation. We insert fiberglass insulation in the shim space between the window frame and rough opening at head and jambs. Sash-weight cavities are always abandoned in the window replacement process; we insulate these as well, being careful not to overfill or compact the insulation. Again, since noise can leak through any air gap, caulking and sealing are important. We set and seal windows and doors in the rough opening with a non-skinning, non-hardening polyurethane or silicone sealant.

Other openings in the building envelope also need attention, such as through-the-wall air-conditioning units, ceiling-mounted attic hatches, and vents. We've developed some simple gasketed covers, made of cabinet-grade plywood, that encapsulate and seal the AC unit and the attic hatch when they're not in use (Figure 5).

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Figure 5. Custom-made insulated plywood covers seal attic hatches (left) and through-wall AC units. Cam-type latches and compressible gaskets ensure a tight seal.

We review vent openings on a case-by-case basis to determine if they constitute a significant noise path that must be treated. We use some simple rules of thumb: First of all, ridge vents, gable vents, and roof louvers must be baffled if their aggregate clear opening area exceeds 1% of the attic floor area. Secondly, bathroom and kitchen vents and range hoods must be baffled or re-ducted if there is an existing line-of-sight path between inside and outside.

Baffles usually need to be custom designed for each particular situation, but the design principles are the same — the baffle should allow free air movement along a circuitous path across absorbent material (Figure 6).

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Figure 6. Roof vents provide a potential path for noise entry. A custom insulation-lined baffle disrupts and muffles sound entering the structure.