Just as there is no such thing as a fireproof building, there is no such thing as a soundproof window. There are however many, and very good, acoustical windows that reduce outside to inside noise. To be effective both the outside noise level and the quietness to be achieved inside must be determined. From these, the reduction level windows can be concluded. As to effectiveness, we had one apartment project that had to meet a 40 dB reduction from outside to inside and could have no operable windows. The result was dwelling units that were so quiet that the owner received resident complaints about background "white noise" from within the units.
If the writer would like to communicate directly with me, I am open to that. As an AIA staff member, I assume you have access to my contact info.
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Craig Hess AIA
Elness Swenson Graham Architects, Inc.
Maplewood MN
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