Sec. 22-430. Design method II.
(a) Generally. Under this article, this method requires the acoustical engineer to follow the design specifications and construction techniques described in this article. an acceptable OITL rating derived as prescribed in this section will be required prior to approval of building plans. The designer or architect is responsible for providing TL ratings for all façade elements, that were determined in accordance with either ASTM E 90 (current revision at time of plans submittal N) or ASTM E 966 (current revision at time of plans submittal).
(b) Noise level reduction requirements. All structures shall be designed and constructed so that the exterior shell of the structure (windows closed) provides a OITL rating, equal to or greater than the minimum values listed in section 22-425. Noise attenuation for remodeling purposes need only be met pursuant to section 146-801(B).
(c) Design calculations. The OITL rating shall be calculated for each room having an exterior façade element (basements are explicitly excluded from rooms requiring calculation), using the composite TL calculation procedure outlined below. The room having the lowest numerical OITL rating will determine if the building meets the minimum requirements. The construction required for this room shall then be applied to the entire building structure; that is the window and door TL ratings shall be applied to all windows in the building, the wall construction shall be applied to all exterior walls in the building, and the roof/ceiling construction shall be applied to all ceiling areas with exterior areas.
In some instances rooms may not have distinct separation lines; i.e., a kitchen adjacent to a family room. For these cases, when the opening between the rooms is at least 50 percent of the area of the separation between the rooms (opening plus wall area) then the rooms may be combined into one room.
The calculations to determine the OITL rating must be performed and stamped by an acoustical engineer, licensed as a professional engineer in the State of Colorado, whom is also a practicing acoustical engineer.
Composite transmission loss values used in the OITL rating calculation are determined as follows. The transmission coefficient (Τ) of a façade element is the ratio of the sound power transmitted through the façade element per unit area to the sound power incident on the façade element per unit area. Transmission loss (TL) is the expression of the transmission coefficient on a decibel scale. The two quantities are related by
TL = 10 Log 10 (1 / Τ)
T = 10 -TL/10
A transmission coefficient of zero, Τ = 0, means that none of the incident sound energy passed through the partition; i.e. the transmission loss is infinity great. A transmission coefficient of one, Τ = 1, means that all of the incident sound energy passed through the partition; i.e. the transmission loss is zero. A TL of zero applied to an open window or door.
The sound energy passing through each component (façade element) of a multielement partition depends on the area and transmission loss of each element. The equation governing this process is
A total T total = A 1 T 1 + A 2 T 2 + A 3 T 3 + A 4 T 4 + ····
Where, A 1 and Τ 1 represent the area and transmission coefficient of the first element (for example a wall), A 2 and Τ 2 represent the area and transmission coefficient of the second element (for example a window), A 3 and Τ 3 represent the area and transmission coefficient of the third element (for example a door), A 4 and Τ 4 represent the area and transmission coefficient of the fourth element (for example a ceiling/roof assembly) and so on. The quantities A TOTAL and Τ TOTAL are for the composite multielement partition. The transmission coefficient for the composite multielement partition is then represented as Τ total = A 1 Τ 1 + A 2 Τ 2 + A 3 Τ 3 + ···/ A total
The TL for the combined multielement partition calculated TL total = 10 Log 10 (1 / T total)
In order to calculate the OITL rating the TL total must be determined for each 1/3-octaveband from 80 to 4000 HZ as described in ASTM E 1332.
(d) Construction. All exterior walls, roofs and exposed floors shall be of airtight construction. All non-lap joints shall be grouted or caulked airtight with a non-hardening, non-shrinking sealant installed in accordance with manufacturer's specifications. Any penetrations of exterior walls or roofs by pipes, ducts or conduits shall be sealed airtight as required for non-lap joints. Door and window openings in exterior walls shall be flashed all around with an approved vapor barrier and sealed to prevent air infiltration. Sill sealant shall be used to prevent air infiltration at all base plates of exterior walls. Attic and crawl space vents shall meet specifications given in sections 22-433 and 22-434. (Ord. No. 2011-07, § 5, 4-11-2011; Ord. No. 2006-78, § 1(Exh. A), 1-8-2007)