Installing an interior window system can be like music to the ears of a typical shareholder or unit owner living in the city that never sleeps. The annoying inherent noises of the city - street, bus and truck traffic, sirens, car alarms, jack hammers and the like - have either been eliminated or significantly reduced from penetrating the sleeping, living and working environments - just by using the right type of window.
Depending on the type and construction, interior windows not only substantially reduce noise but eliminate drafts and dirt infiltration, provide maximum thermal control, security and privacy and protect furnishings, artwork, equipment and data from dirt, soot, humidity and sunlight. All of this is done without touching or affecting the existing exterior windows.
An interior window used for sound reduction purposes should be an independent secondary window, not fastened in any way to the existing exterior window. Direct physical contact or structural coupling can reduce the sound reduction performance. This is the result of exterior sound vibrating through the exterior window, which is then transmitted by contact to the interior window. In addition, the attachment of the interior window to an exterior window often leaves cracks uncovered, therefore not always fully attenuating sound transmission through frame openings.
For best results the interior window should be glazed with laminated glass (1/4", 3/8", 1/2" or 3/4" thick), and installed creating a "buffer zone" or so-called airspace, and seal between the existing exterior window and the new interior window. It must be well sealed and should be as generously spaced as possible away from the exterior window.
Furthermore, the exterior window and interior window sound reduction performance is extremely sensitive to sound leakage through frame openings. Therefore, the use of an interior window system to improve sound isolation should be accompanied by a properly sealed exterior window.