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Noise Management and Public Response 107 Difference between Interior and Exterior Sound Levels and Methods to Abate Each The abatement of noise inside a structure is largely based on structural modifications to the receiving building, while abatement of noise outside a structure is focused on its source. As a rule of thumb, aviation noise levels are reduced by approximately 15-20 decibels between exterior and interior measurements for well-constructed buildings in the middle latitudes. When windows remain closed year-round or the structure is in higher latitudes and well-insulated to retain heat, the difference between levels may average somewhat higher, while in the tropics or sub-tropics where windows remain open for much of the year, the difference between outdoor and indoor noise levels from an aircraft overflight may be less. Interior Noise Abatement The purpose of a sound insulation program is to reduce the adverse impacts of aircraft noise on residents near an airport. In general, sound insulation programs help to preserve neighbor- hoods and communities, improves homes and neighborhoods, and makes the interior of homes more inhabitable. The major paths for noise transmission into a house in order of importance are: gaps and cracks, windows and doors, and walls and roof. Therefore, the generalized acoustical approach for treat- ment protocols would be to: eliminate all openings and flanking; improve all windows and doors; improve walls and ceilings; add mechanical ventilation or central air conditioning; and treat attic spaces and/or roof structures. Windows treatments would include replacing existing windows with single- or double-pane acoustical windows that may include monolithic or laminated glass and also may include a storm window depending upon the noise reduction requirements. Specialty windows such as bay, bow, stained glass, or garden windows are evaluated on a case-by-case basis for treatment requirements. Windows in unfinished attics, attached garages, and unfinished basements are typically not treated, although the windows may be replaced with a nonacoustical window to maintain the similar look on the outside of the house. Door treatments are likely to include replacing existing doors with acoustically rated or solid wood doors making sure the door and frame have good seals and gaskets. Storm doors are added depending upon noise reduction requirements. Specialty doors such as sliding patio doors and French doors also are treated. Doors to basement areas, attached garages and finished attic spaces are usually not treated, while a door to an unfinished attic may be treated. Roof treatments are usually not required in homes with normal attic space although additional batting or blown-in insulation may be added. Hatches to attic spaces may be covered with batt insu- lation and the opening resealed and regasketed. For homes with vaulted or cathedral ceilings, acoustical treatment is evaluated on a case-by-case basis. Additional gypsum board may be added to the interior ceiling in some cases to build up the noise reduction capabilities of the ceiling. Wall treatments are rarely required, except in extremely high noise areas. In those cases, addi- tional gypsum board may be added to the interior walls to build up the noise reduction capabilities of the exterior walls. The HVAC system of each home is also evaluated and treated. Installation may include either a central air conditioning or whole house ventilation system. For homes with a forced air system, a central air conditioning system will be installed as required. Existing furnaces may be upgraded