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
***************************
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BARRIER DATA
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BARRIER HEIGHTS
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REC REC ID DNL PEOPLE feBQ(CAL)
1
2
3
4
5
6
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8
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1-Up
2 -Down
2 -Up
3 -Down
3 -Up
4 -Down
4 -Up
5 -Down
5-Up
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67.
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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.