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HomeMy WebLinkAboutCT 98-23; La Costa Greens; Tentative Map (CT) (17)Giroux & Environmental Consultants MAR 05 1999 LA COSTA GREENS P.U.D. CITY OF CARLSBAD, CALIFORNIA Prepared for: Legacy Development Attn: Mark J. Goethals 2614 Unicornio Street La Costa, CA 92009 cc: Crosby, Mead, Benton & Assoc, Attn: Kathi Gerritsen 5650 El Camino Real, Suite 200 Carlsbad, CA 92008 Date: March 1, 1999 Prepared by: Hans D. Giroux Acoustical Consultant Giroux & Associates 17744 Sky Park Circle, Suite 210, Irvine, California 92614 - Phone (949) 851-8609 - Fax (949) 851-8612 1STOISE SETTING Sound is mechanical energy transmitted by pressure waves in a compressible medium such as air. Noise is generally defined as unwanted sound. Sound is characterized by various parameters that describe the rate of oscillation of sound waves, the distance between successive troughs or crests, the speed of propagation, and the pressure level or energy content of a given sound wave. In particular, the sound pressure level has become the most common descriptor used to characterize the loudness of ambient sound. The unit of sound pressure level ratioed to the faintest sound detectable by the human ear is called a decibel (dB). *t Because sound or noise can vary in intensity by over one million times within the range of human hearing, a logarithmic loudness scale is used to keep sound intensity numbers at a convenient and manageable level. Since the human ear is not equally sensitive to all sound frequencies within the entire audible spectrum, noise levels at maximum human sensitivity (middle A and its higher harmonics) are factored more heavily into sound descriptions in a process called "A-weighting," written as dB(A). Any further reference to decibels written as "dB" should be understood to be A- weighted. Time variations in noise exposure are typically expressed in terms of a steady-state energy level equal to the energy content of the time varying period (called Leq), or, alternatively, as a statistical description of the sound level that is exceeded over some fraction of a given observation period. Finally, because community receptors are more sensitive to unwanted noise intrusion during the evening and at night, State law requires that, for planning purposes, an artificial dB increment be added to quiet time noise levels in a 24-hour noise descriptor called the Community Noise Equivalent Level (CNEL). An interior CNEL of 45 dB(A) is mandated by the State of California Noise Insulation Standards (CCR, Title 24, Part 6, Section T25-28) for multiple family dwellings and hotel and motel rooms. The Code requires that any multiple family unit exposed to an exterior noise loading in excess of 60 dB CNEL must be certified that the interior meets the 45 dB CNEL standard. The Code similarly requires an acoustical analysis for project proximity to airports or operating railroads. If the 45 dB CNEL standard can only be met in the window closed position, supplemental ventilation to allow such window closure must be provided. In 1988, the State Building Standards Commission recommended that this standard be expanded to include all habitable rooms of all dwelling units. The City of Carlsbad has adopted that recommendation and requires structural noise reduction to be capable of achieving an interior level of 45 dB CNEL. An interior standard of 45 dB CNEL is thus appropriate for the proposed project. Structural noise attenuation with closed windows for standard construction design is around 20 dB. A level of 65 dB CNEL thus can be attenuated to 45 dB as long as windows can be closed to shut out roadway noise. The ability to close the window requires that supplemental ventilation be provided to compensate for the limitations on opening windows for fresh air. If noise levels exceed 65 dB CNEL at the building facade, upgraded noise reduction features are generally necessary to achieve the interior standard. Because windows are the acoustically "weakest" structural component in a dwelling, acoustically rated windows are the first upgrade usually applied to attain the 45 dB CNEL interior standard. The City of Carlsbad has established a noise ordinance that is designed to protect citizens from excessive noise exposure from those sources over which the City may exercise legal control. However, traffic noise is preempted from local control by state and/or federal agencies. The City of Carlsbad only has the authority to 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: CITY OF CARLSBAD Q joise Guidelines Manual FIGURE 1 LAND USE COMPATIBILITY FOR COMMUNITY NOISE ENVIRONMENTS MATRIX Land U«« Cat* gory Community Noise Exposure CNEL. dB 60 65 70 75 Residential • (all) Single Family, Duplex. Mobilehome Multi Family, ate. Transient Lodging Motel. Hotel School. Library, Church, Hospital, Nursing Home Auditorium, Concert Hall. Amphitheater Sports Arena, Outdoor Spectator Sport* Playground, Neighborhood Park •X-X•mm Golf Course, Riding Stable. Water Recreation, Cemetery Office Building, Business Commercial Planned Industrial and Professional Generel Industrial, Manufacturing, Utilities, Agriculture INTERPRETATION: Normally Acceptable Specified land use is satisfactory. bated upon the assumption that any building* involved are of normal conventional construction, without any special noise insulstlon requirement*. Conditionally Acceptable New construction or development should be undertaken only after a detailed analysis of the noi*e reduction requirement* i* made and needed noli* insulation features included in the design. Conventional construction, but with closed window* and fresh air supply systems or air conditioning will normally «uf(ic*. Normally Unacceptable New construction or development •hould generally be discouraged. If new construction or development doee proceed, a detailed analysis of the noise reduction requirements must be made and needed noiee insulation features included in the design. Land Uee Discouraged New construction or development should generally not be undertaken. NOTE: McClellan Pelomar Airport Noise Is regulated by the Airport Comprehensive Land Use Plan (CLUP). See the CLUP lor airport noise compatibility guidalinti. Project Processing Procedures 25 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 at any usable outdoor space, plus the indicated structural noise reduction as a function of exterior loading, are therefore the analysis criteria for the proposed La Costa Greens development. IMPACT ANALYSIS The project site noise levels will derive exclusively from traffic on La Costa Avenue. The project site is far from any noise influence for McClennan-Palomar Airport, and adjacent golf course operational activities create minimal noise except for an occasional mower. Buildout traffic noise on La Costa Avenue has been calculated in the "Noise Guidelines Manual" for Year 2010 buildout traffic conditions. This calculation, from Appendix C of the guidelines, was used to determine the future design level noise loading on the project. The predicted buildout noise level is 75.6 dB CNEL at 50 feet from the roadway centerline. This level will be attenuated by distance spreading, and very significantly by the grade separation between the roadway and the houses. The top of the slope will act as a noise attenuating berm that will reduce noise levels by 10 dB or more from a direct line-of-sight condition. 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 SOUND32 matched the predicted CNEL from the "Guideline" document. The SOUND32 input and output data files are attached as an appendix. Noise levels were calculated at the facade of each building as shown on the tentative map dated 12-21-98. A calculation was made for the downstairs and upstairs of each structure. Any patio or other usable outdoor space will be at the rear of the houses facing the golf course. The house itself will shield such area from traffic noise. The only noise issue is therefore the building facade level relative to meeting the interior standard of 45 dB CNEL. The noise exposure at each building facade is shown in the SOUND32 model printout to be as follows (dB CNEL): LOT 1 2 3 4 5 Downstairs 59 59 60 60 60 Upstairs 61 61 61 62 62 As previously noted, structural noise attenuation requirements are as follows: Noise Loading; Mitigation; < 57 dB CNEL None Required 57-65 dB CNEL Window closure and supplemental ventilation > 65 dB CNEL Upgraded windows and supplemental ventilation All habitable rooms along the southern development facade facing La Costa Avenue will have an intermediate exposure within the 57-65 dB CNEL range. No window or other upgrades are required. However, window closure must be an option for such rooms. Supplemental ventilation meeting UBC/CBC requirements of at least two air changes per hour with at least 20 percent fresh make-up is required. Most agencies accept central air conditioning with a "fan only" setting as meeting this requirement. CONCLUSIONS: 1. Exterior noise exposure is not an issue. Usable exterior space (patio, etc.) will be protected by the building mass and the additional source-receiver distance within the yards facing the golf course. 2. Interior standards will not require any acoustical upgrades. "Standard" windows will meet any noise protection requirements as long as supplemental ventilation supports the option to shut windows to keep out roadway noise. SOUISTD32 NOISE MODEL - INPUT DATA SHEET - BUILDING FACADE EXPOSURE (dB CNEL) AT LOTS 1-5 (Downstairs and Upstairs) La Costa Road T-Buildout Condition, 1 1958 , 50 , 36 , 50 , 6 , 50 T-Buildout Condition, 2 1958 , 50 , 36 , 50 , 6 , 50 L-Westbound Traffic, 1 N,0.,1016,54, N,1000.,1016,54, N,1200. ,1016,44, N,2000. ,1016,44, L-Eastbound Lanes, 2 N,0.,984,54, N,1000.,984,54, N,1200.,984,44, N,2000.,984,44, B-Top of Slope, 1,1,1,1 0.,1042,53,55, 1000.,1042,53,55, 1200.,1042,43,45, 2000.,1042,43,45, R, 1 , 67 ,500 1025,1182,35.,1-Down R, 2 , 67 ,500 1025,1182,45.,1-Up R, 3 , 67 ,500 1065,1180,35.,2-Down R, 4 , 67 ,500 1065,1180,45.,2-Up R, 5 , 67 ,500 1100,1176,35.,3-Down R, 6 , 67 ,500 1100,1176,45.,3-Up R, 7 , 67 ,500 1140,1179,35.,4-Down R, 8 , 67 ,500 1140,1179,45.,4-Up R, 9 , 67 ,500 1175,1189,35.,5-Down R, 10 , 67 ,500 1175,1189,45.,5-Up C,C SOUND32 - RELEASE 07/30/91 TITLE: La Costa Bead EFFECTIVENESS / COST RATIOS *************************** BAR ELE 1 2 3 0 1 - 56. - 66. - 57. 2 51 61 53 .* . * .* 3 4 51. 62. 53. 567 Bl Bl Bl PI P2 P3 BARRIER DATA ************ BAR ELE 1 2 3 BARRIER HEIGHTS 0 1 1. 1. 1. 2 2 2 2 .* .* .* 345 3. 3. 3. BAR 6 7 ID Bl Bl Bl PI P2 P3 LENGTH TYPE 1000 200 800 .0 .2 .0 BERM BERM BERM 0 REC REC ID DNL PEOPLE feBQ(CAL) 1 2 3 4 5 6 7 8 9 10 I -Down 1-Up 2 -Down 2 -Up 3 -Down 3 -Up 4 -Down 4 -Up 5 -Down 5-Up 67. 67. 67. 67. 67. 67. 67. 67. 67. 67. 500. 500. 500. 500. 500. 500. 500. 500. 500. 500. 58.9 60.7 59.3 61.1 59.7 61.4 60.0 61.7 60.0 61.6 BARRIER TYPE BERM MASONRY MASONRY/JERSEY CONCRETE COST 17502, 0. 0. 0. TOTAL COST = $ 18000. BARRIER HEIGHT INDEX FOR EACH BARRIER SECTION 222 CORRESPONDING BARRIER HEIGHTS FOR EACH SECTION 2. 2. 2.