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.