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HomeMy WebLinkAboutCT 99-08; Spyglass II; Tentative Map (CT) (77)Giroux & Associates Environmental Consultants NOISE ANALYSIS SPYGLASS RESIDENTIAL DEVELOPMENT CITY OF CARLSBAD, CALIFORNIA Prepared for: Landis Industries, Inc. Attn: John L. Wismer 24711 Venablo Lane Mission Viejo, CA 92691 Date: May 10, 1999 MAY 1 1 1999 CITY OF CARLSBAD PLANNING DEPT. 77744 Sky Park Circle, Suite 210, Irvine, California 92614 - Phone (949) 851-8609 - Fax (949) 851-8612 more current data and recommended new analysis protocols in determining any noise mitigation needed to create project compatibility with City of Carlsbad noise standards. Noise Metrics "Noise" is defined as unwanted sound. Ambient sound is comprised of vibrations of air molecules that experience continually variable amplitude across the entire frequency spectrum. Because it would take an infinite amount of resource to describe this variation in all space and all time, various averaging techniques have been developed to better describe the complex dynamics of sound waves. The square of the sound pressure level created by vibrating molecules logarithmically ratioed to the square of the lowest sound pressure level detectable by a young person with good auditory acuity is called a decibel (dB). The energy averaged sum of all noise intensities over all frequencies is called the noise equivalent level, written as "Leq". Because the human ear is less sensitive to high and low frequencies, a weighting curve is normally applied to the frequency spectrum to accentuate the noise at frequencies of maximum human sensitivity in a process called "A- weighting," written as "dBA". Because people are more noise-sensitive at night when background levels are lowest and when they are engaged in quiet activities such as sleeping, artificial noise metrics have been developed to- account for this heightened sensitivity. For land use planning, a weighted 24-hour scale called the Community Noise Equivalent Level (CNEL) is used. CNEL is calculated as the 24-hour average of all Legs from 7 a.m. - 10 p.m., (Leq +5) from 7 p.m. to 10 p.m., and (Leq +10) from 10 p.m. to 7 a.m. Because of the nocturnal penalty, CNEL and the noisiest one-hour Leq often differ by less than ± 2 dB. Land use compatibility with the ambient noise environment varies with types of land use. Residences, schools, churches, health care facilities or libraries are maximally noise sensitive. Industrial or agricultural uses are minimally affected by background noise. Figure 1 shows the noise/land use compatibility matrix for various types of land uses in Carlsbad. All residential uses, except for transient lodging, are afforded the highest degree of noise protection. Applicable Noise Standards Traffic noise is preempted from local control by state and/or federal agencies. The City of Carlsbad has the authority to CITY OF CARLSBAD Noise Guidelines Manual FIGURE 1 LAND USE COMPATIBILITY FOR COMMUNITY NOISE ENVIRONMENTS MATRIX Land Use Category Residential • (all) Single Family, Duplex, Mobilehom*. Multi-Family, etc. Transient Lodging • Motet, Holal School, Library, Church, Hospital, Nursing Horn* Auditorium, Concert Hall. Amphithaatar Sports Arena, Outdoor Spectator Sport* Playground, Neighborhood Park Golf Course, Riding Stable. Water Recreation, Cemetery Olfice Building, Business Commercial Planned Industrial end Piofosaional General Induttriel, Manufacturing, Utilities, Agriculture 55 Community Noise Exposure CNEL, dB 60 65 70 75 80 INTERPRETATION: Normally Acceptable Specified land us* is satisfactory, bated upon the assumption that any building* involvad are of normal conventional construction, without any special noise Insulation requirements. Conditionally Acceptable Naw construction or development should be undertaken only after a detailed analysis of tho noisa reduction requirements is made and needed noit* insulation features included in the design. Conventional construction, but with closed windows and fresh air supply systems or air conditioning will normally suffice. Normally Unacceptable Naw construction or development should generally be discouraged. II new construction or development doe* proceed, • detailed analysts of the noise reduction requirements must be made and needed noise insulation feature* included in the design. land Us* Discouraged New construction or development should generally not be undertaken. NOTE: McClellan Palomar Airport Noise Is regulated by the Airport Comprehensive Land Use Plan (CLUP). See the CLUP for eirport noisa compatibility guideline*. Project Processing Procedures 25 enforce vehicle noise standards in the motor vehicle code, but not to establish unique performance standards for vehicles operating within the city. Since noise can not be controlled at the source, the City regulates the levels to which a receiver may be exposed through its land use decision authority. The City has thus adopted noise standards for various types of land uses as shown in Figure 1 which must be achieved before a project may be approved. Unless there are compelling overriding considerations, the following noise exposure standards must be attained at residential uses: Usable outdoor space (patio, spa, deck, etc.) - 60 dB CNEL Habitable interior space (bedrooms, etc.) - 45 dB CNEL The "Noise Guidelines Manual" states that the exterior-to-interior attenuation of traffic or other noise in residential structures is 12 dB if windows are open, and 20 dB if single-pane windows are closed. To achieve structural attenuation exceeding 20 dB, upgraded features such as closed dual-paned windows are necessary. The hierarchy of residential structural noise reduction is as follows: Exterior @ Facade: Attenuation Requirements: 57 dB CNEL None 57-65 dB CNEL Close windows facing street, provide supplemental ventilation to affected rooms per building code. > 65 dB CNEL Upgrade windows, possibly double wall boards on resilient fasteners, add duct/vent lining and provide supplemental ventilation. Attainment of a 60 dB CNEL exterior level plus the indicated structural noise reduction as a function of exterior loading, are therefore the analysis criteria for the proposed Spyglass development. Impact Analysis Noise level calculations had been prepared for project site frontage along El Camino Real and Carlsbad Village Drive based upon future traffic forecasts using the federal highway traffic noise prediction model (FHWA-RD-77-108) . These values were compared to the noise impact table in Appendix C of the City of Carlsbad Noise Guidelines Model for Year 2010 traffic volumes. The "Guidelines" design levels for El Camino Real and for Carlsbad Village Drive were substantially higher than those used in the 1989 study. The comparison of the previous study with the Guidelines levels was as follows: Distance to: CNEL @ 50' 70 CNEL 65 CNEL 60 CNEL El Camino Real: 1989 Study 1995 Guidelines Difference 76.4 79.9 + 3.5 90' 229' +139' 290' 494' +204' 625' 1063' +438' Carlsbad Village Drive: 1989 Study 68.5 1995 Guidelines 72.8 Difference +4.3 < 50' 77' 55' 166' +111' 185' 358' +173' Required noise mitigation based upon the 1995 Guidelines is therefore 3.5 - 4.3 dB more stringent than previously anticipated. Previous barrier calculations, however, did not fully incorporate the enhanced noise attenuation created by the grade separation between the building pads and the adjacent roadways. The greater level of required mitigation from the more current traffic projections is somewhat offset by the better than anticipated noise reduction from substantial source-receiver grade separation. Attenuation calculations were performed using the Caltrans SOUND32 version of the federal FHWA-RD-77-108 model. SOUND32 better incorporates the variable effects of terrain and grade separation than any other computer noise model. SOUND32 was initialized with the recommended City of Carlsbad traffic mix (auto/medium truck/ heavy truck) and then the volumes were adjusted until the predicted one-hour Leq in SOUNDS2 matched the predicted CNEL from the "Guideline" document. The noise attenuation for the barrier array suggested in the 1989 study was evaluated in terms of the height needed to meet the standard. Any exterior-to-interior attenuation requirements were also reevaluated. Exterior Noise Standards Compliance The City of Carlsbad Noise Guidelines Manual requires that a noise analysis consider the distinction between acoustically "soft" and "hard" surfaces. A soft surface occurs when irregular terrain, short barriers or other non-reflective elements prevent perfect reflection from the ground. Hard surfaces occur when the intervening ground is paved, or when the sound wave travels well above the ground surface without any partial absorption. The propagation between El Camino Real or Carlsbad Village Drive to any rear yards was considered a soft site condition. Noise impacting second-story facades was considered a hard site condition. Lots 3, 4, 5, 6, 17, 18 and 19 facing El Camino Real have their outdoor recreational areas protected by the house itself. The combined effects of the structure grade separation and distance' create noise levels that are less than 60 dB CNEL at the rear yard, patio, spa, etc. area. The upstairs on these units, however, will experience a 73 dB CNEL on front-facing rooms and thus require enhanced structural attenuation. At Lot 6, the side yard will be exposed to noise from El Camino Real. The City of Carlsbad "Noise Guidelines Manual" requires that the receiver exposure be calculated at a point 20 feet away from the top of slope. At this location, the house itself will protect about 90 degrees of the field of view, and the intervening steep slope (50 feet grade separation) will create "soft" site propagation conditions. The traffic noise level at the Lot 6 patio area will be 66 dB CNEL. The 6 dB reduction needed to achieve the City of Carlsbad 60 dB exterior standard can be achieved by a 3- foot barrier at the top of slope. A 3 foot barrier (concrete block or stucco) with wrought iron above is a popular top of slope treatment that preserves distance view sheds, provides children safety, and blocks out near-field traffic noise. Lot 2 will experience noise from El Camino Real along its side yard, and from both El Camino Real and Carlsbad Village Drive in its backyard. Lots 1 and 9-12 will be mainly affected by Carlsbad Village Drive. With lower traffic volumes on this roadway than on El Camino Real, noise mitigation requirements for homes with Carlsbad Village Drive frontage will be less than along El Camino Real. Barrier height calculations for exterior noise along Carlsbad Village Drive range from 6 feet along the north side of Lot 2 to 3 feet along Lots 9-12. The side yard of Lot 2 similarly requires a 6-foot barrier to accommodate its closer distance to El Camino Real. The barrier heights needed to attain an acceptable exterior noise level are shown in Figure 2 and are summarized as follows: Lot 1 - 5' wall at top of slope Lot 2 - 6' wall facing Carlsbad Village Road Lot 6 - 3' side yard wall at top of slope Lot 9 - 3' wall at top of slope Lot 10 - 3' wall at top of slope Lot 11 - 3' wall at top of slope Lot 12 - 3' wall at top of slope Interior Noise Standards Compliance Upstairs windows of homes with frontage along both El Camino Real and Carlsbad Village Drive will have a more direct view of traffic less protected by the project/roadway grade separation than downstairs backyard recreational areas. In the absence of ground absorption, upstairs building facade noise levels at the first tier of homes along each roadway will be in the upper-60 to lower-70 dB CNEL range. Structural noise attenuation in the mid- to high-20 dB range will be needed to achieve a 45 dB CNEL interior level. Second-story building facade noise levels were calculated for each lot with arterial frontage containing a two-story building. Table 1 summarizes the exterior facade noise loading of all proposed units with arterial frontage. The Carlsbad Village Drive frontage will have noise levels of 66-69 dB. Structural noise reduction of 21-24 dB will be needed to meet the 45 dB interior standard. Such reduction will require the ability to close windows and use of slightly upgraded (thicker glass) single-pane sliders. If air conditioning and dual-paned windows are made standard features of each home, the 45 dB CNEL standard will be met with an adequate margin of safety. CARLSBAD .TRACT FIGURE 2 - NOISE BARRIER REQUIREMENTS BUILDING FACADE NOISE LOADING EL CAMINO REAL CARLSBAD VILLAGE DR. Lot No. 1 2 3 4 5 6 9 10 11 12 17 18 19 Distance 200' 240' 240' 240' 240' 230' 230' 240' CNEL* 74 73 73 73 73 73 73 73 Distance 120' 160' 220' 160' 1307 120' ___ _ CNE1 69 68 66 68 69 69 __« = in dB CNEL for acoustically "hard" conditions Along El Camino Real, the noise loading will be 73-74 dB CNEL despite considerable distance and grade separation. This will require 28-29 dB of noise reduction to meet the interior standard. Such reductions require somewhat more upgraded features. Windows, the acoustically weakest component, will need to be fairly high quality dual-paned units. If other "flanking paths" such as vents, ducts, door seals, etc. are minimized, the sound transmission class (STC) of bedroom or living room windows is generally equal to the noise level reduction (NLR) of the building envelope. Adequate structural integrity plus STC=29 or better windows are recommended to meet interior standards. The appendix contains a "standard" building package rated at NLR=30. Adoption of the structural recommendations in this package is encouraged to allow the 45 dB CNEL interior standard to be met with an adequate margin of safety. SUMMARY: Table 2 summarizes the requirements for the proposed Spyglass development to meet City of Carlsbad interior and exterior noise standards. 10 NOISE MITIGATION SUMMARY Lot No. 1 10 11 Exterior Mitigation 5' Barrier (E-N property line) 6' Barrier (N-W property line) None Required None Required None Required 3' Barrier* side lot line 3' Barrier* rear lot line 3' Barrier* rear lot line 3' Barrier* rear lot line Interior Mitigation Slightly upgraded windows & supplemental ventilation Highly upgraded windows & other nois-e control features shown in Appendix Slightly upgraded windows and supplemental ventilation Slightly upgraded windows and supplemental ventilation Slightly upgraded windows and supplemental ventilation Slightly upgraded windows and supplemental ventilation Highly upgraded windows & other noise control features shown in Appendix Highly upgraded windows & other noise control features shown in Appendix Highly upgraded windows & other noise control features shown in Appendix Continued on Next Page Table 2 Page Two Lot No.Exterior Mitigation Interior Mitigation 12 3' Barrier* rear lot line 17 18 19 None Required None Required None Required Highly upgraded windows & other noise control features shown in Appendix Slightly upgraded windows & supplemental ventilation Slightly upgraded windows & supplemental ventilation Slightly upgraded windows & supplemental ventilation Probably a 3-foot solid base plus wrought iron on top. NLR =30 PACKAGE RECOMMENDED FOR EL CAMINO REAL FRONTAGE -1- RECOMMENDED BUILDING REQUIREMENTS FOR A MINIMUM NOISE LEVEL REDUCTION OF 30 dB 1. Compliance Compliance with the following standards shall be deemed to meet the requirements of the Compatible Use Districts in which an NLR 30 is specified. 2. General a. Brick veneer, masonry blocks or stucco exterior walls shall be constructed airtight. All joints shall be grouted or caulked airtight. b. At the penetration of exterior walls by pipes, ducts or condyits, the space between the wall and pipes, ducts or conduits shall be caulked or filled with mortar. c. Window and/or through-the-wall ventilation units shall not be used. d. All sleeping spaces shall be provided with either a sound-absorbing ceiling or a carpeted floor. e. Through-the-walI/door mailboxes shall not be used. 3. Exterior Walls a. Exterior walls other than as described below shall be constructed to have a sound transmission class rating of at least STC-44. b. Stud walls shall be at least 4" in nominal depth and shall be finished on the outside with siding-on-sheathing, stucco, or brick veneer. -2- (1) Interior surface of the exterior walls shall be of gypsum board or plaster at least 1/2" thick, installed on the studs. The gypsum board or plaster may be fastened rigidly to the studs if the exterior is brick veneer or stucco. If the exterior is siding-on-sheathing, the interior gypsum board or plaster must be fastened resiliently to the studs. (2) Continuous composition board, plywood or gypsum board sheathing shall cover the exterior side of the wall studs behind wood, or metal siding. The sheathing and facing shall weigh at least 4 pounds per square foot. (3) Sheathing panels shall be butted tightly and covered on the exterior with overlapping building paper. The top and bottom edges of the sheathing shall be sealed. (4) Insulation material at least 2" thick shall be installed continuously throughout the cavity space behind the exterior sheathing and between wall studs. Installation shall be glass fiber or mineral wool. 4. Windows a. Windows other than as described in this section shall have a laboratory sound transmission rating of at least STC-29. b. Glass of double-glazed windows shall be at least 1/8" thick. c. Double-glazed windows shall employ fixed sash or efficiently weather stripped operable sash. The sash shall be rigid and weather stripped with material that is compressed air tight when the window is closed so as to conform to an infiltration test not to exceed 0.5 cubic foot per minute per foot of crack of length in accordance with ASTM E-283- 65-T. d. Glass of fixed-sash windows shall be sealed in an airtight manner with a non-hardening sealant, or a soft elastomer gasket or glazing tape. e. The perimeter of window frames shall be sealed airtight to the exterior wall construction with a sealant conforming to one of the following Federal Specifications: TT-S-00230, or TT-S-00153. f. The total area of glass of both windows and exterior doors in sleeping spaces shall not exceed 20% of the floor space. -3- 5. Doors a. Entry doors shall be 1-3/4" minimum thickness with solid cores and shall be equipped with weather stripping and compression seals. b. The glass of double-glazed sliding doors shall be separated by an airspace. Each sliding frame shall be provided with an efficiently airtight weather stripping material as specified in Section 4C. c. Glass of all doors shall be at least 3/16" thick. Glass of double sliding doors shall not be equal in thickness. d. The perimeter of door frames shall be sealed airtight to the exterior wall construction. e. Glass of doors shall be set and sealed in an airtight non-hardening sealant, or a soft elastomer gasket or glazing tape. 6. Roofs a. Combined roof and ceiling construction other than described in this section and Section 7 shall be constructed to achieve a sound transmission class rating of at least STC-44. b. With an attic or rafter space at least 6" deep, and with a ceiling below, the roof shall consist of closely butted 1/2" composition board, plywood or gypsum board sheathing topped by roofing as required. c. If the underside of the roof is exposed, or if the attic or rafter spacing is less than 6", the roof construction shall have a surface weight of at least 40 pounds per square foot. Rafters joists, or other framing may not be included in the surface weight calculation. d. Window or dome skylights shall have a laboratory sound transmission class rating of at least STG-33. 7. Ceilings a. Gypsum board or plaster ceilings at least 1/2" thick shall be provided where required by Paragraph 6.b above. Ceilings shall be substantially airtight, with a minimum number of penetrations. b. Glass fiber or mineral wool insulation at least 3.5" thick shall be provided above the ceiling between joists. -4- 8. Floors The floor of the lowest occupied rooms shall be slab on fill, below grade, or over a fully enclosed basement. All door and window openings in the fully enclosed basement shall be tightly fitted. 9. Ventilation a. A mechanical ventilation system shall be installed that will provide at least 2 air changes per hour with at least 20% fresh air supply requirements for various use in occupied rooms without the need to open any windows, doors, or other openings to the exterior. b. Gravity vent openings in attic shall not exceed code minimum in number and size. The openings shall be fitted with transfer ducts at least 3 ft. in length containing internal sound absorbing duct lining. Each duct shall have a lined 90° bend in the duct such that there is no direct line of sight from the exterior through the duct into the attic. c. All vent ducts connecting the interior space to the outdoors, except in domestic range exhaust ducts, shall contain at least a 10 ft. length of internal sound absorbing duct lining. Each duct shall be provided with a lined 90° bend in the duct such that there is no direct line of sight through the duct from the venting cross section to the room opening cross section. d. Duct lining shall be coated glass fiber duct liner at least 1" thick. e. Domestic range exhaust ducts connecting the interior space to the outdoors shall contain a baffle plate across the exterior termination which allows proper ventilation. The dimensions of the baffle plate should extend at least one diameter beyond the line of sight into the vent duct. The baffle plate shall be of the same material and thickness as the vent duct material. g. Building heating units with flues or combustion air vents shall be located in a closet or room closed off from the occupied space by doors.