Windows are usually the weakest part of a residence in terms of exterior-to-interior noise reduction. Typical operable windows have Sound Transmission Class (STC) values between 20 and 30 dB whereas the rating needed to reduce aircraft noise intrusion is between 35 and 45 dB, depending on the severity of the noise.* Single and dual (thermal) paned operable windows cannot achieve much more than about 33 dB, even with specialty glass such as laminated glass. The achievement of higher STC ratings mainly depends on placing a fairly large air gap (about 2 inches) between two windows of unequal glass thickness. This can be done by adding a secondary window to existing one or by replacing the existing one with a double window assembly.
Exterior doors of lightweight (hollow-core or panel) materials are also very significant transmission paths for noise intrusion. In most cases, such doors need to be replaced by a solid core door with an STC rating of between 35 and 40 dB. Sliding glass doors meeting such rating values would be much too heavy and would require an inordinate amount of opening force. The best available solution is to add a secondary sliding glass door to the existing one.
Wood frame wall structures with stucco exterior and gypsum board interior cladding are normally sufficient for sound insulation. However, if the noise exposure is exceptionally high or the cladding is lightweight it may be necessary to add interior secondary partitions to the existing structure. This is considered on a room-to-room basis and would not include kitchens, bathrooms, or other minor areas of a dwelling.
Roof and Attics
Most roof structures can be improved to meet sound insulation goals by simply adding thermal insulation materials to the attic space. These materials absorb sound as it reverberates (echoes) around the attic, and improve the overall noise reduction from outside to beneath the ceiling of a room.
The benefits of sound insulation can only be achieved with windows and doors closed. This means that ventilation (air) should be provided through a system, which does not allow noise penetration. Various types of ventilation systems have been shown to provide this capability.
Other seemingly simple noise penetration areas of a dwelling can become extremely significant and noticeable when windows and doors have been insulated. Obvious examples are through-the-wall openings (for mail slots and ventilation) and chimneys. Mail slots and ventilation openings should be sealed and replaced with alternatives. Chimneys can be improved by addition of a damper which provides a good seal when closed, but this effective only when the fireplace is not used. A glass screen at the fireplace is also beneficial for noise reduction. Similarly, crawlspace vents can be significant noise paths in an otherwise sound insulated home. These may require the installation of noise control louvers or baffles to reduce noise penetration into the crawlspace and through floors.
*STC is a rating method described in American Society for Testing and Materials (ASTM) Standard E413 and is used extensively by suppliers of noise reduction products. Its application to aircraft noise projects requires supplementary consideration of low-frequency noise reduction.