HomeMy WebLinkAbout4.3 4,
TOWN OF Los ALTOS HILLS February 8, 1995
Staff Report to the Planning Commission
RE: REQUEST FOR SITE DEVELOPMENT PERMIT FOR A NEW
RESIDENCE; LANDS OF HONG; 26370 GINNY LANE.
FROM: Susan Manca,Planner
RECOMMENDATION That the Planning Commission EITHER:
1. Continue consideration of the requested site development permit for
revisions;
OR
2. Approve the requested Site Development Permit,subject to the
recommended conditions.
DISCUSSION:
Site Data:
Net Lot Area: 1.252 acres
Average Slope: 4.0%
Lot Unit Factor: 1.25
Floor Area and Development Area:
Area Max. Prop. Exist. Incrs. Left
Devel. 18,750 .: 10,586 2,257 8,329 +8,164
Floor 7,500 6,478 1,957 4,521 +1,022
Planning Commission '
February 8, 1995
Lands of Hong
Page 2
The applicant is requesting approval of a Site Development Permit for a new
residence. The parcel is lot 2 in the Taaffe Partition of the Rancho La Purissima
Concepcion Subdivision. The property is located on the northeast end of Ginny
Lane and abuts the 280 Freeway along the southwest property line.
The existing buildings on the property include a small cottage with 1,245 square
feet which encroaches into the side yard setback, a garage, and 3 storage sheds,2
of which encroach into the rear yard setback. Two existing sheds and the garage
are proposed to be demolished.
The applicant proposes to keep the 460 square foot shed which is located within
the rear setback of the lot. It was built approximately 15 years ago without
permits by the previous owner. Staff requested removal or relocation of the shed
in 1982 when the Town received a request for a second shed (see Attachment 2),
however,this has not been accomplished. Staff has included as a condition of
approval for the new residence that the applicant either remove or relocate the
shed out of the setback.
The existing cottage is to be modified by removing 245 square feet so that it can
remain on the site as a secondary unit. This building is located within the side
setback. The applicant proposes the demolition of 195 square feet along the west
side of the building and the conversion of fifty square feet of floor area into an
open patio. The cottage will therefore meet the 1,000 square foot maximum for a
secondary unit. Although the cottage is within the side setback on the eastern
and northern sides of the property, the applicant is proposing the demolition of
the western section of the building. The kitchen is located along the eastern side
of the building and the applicant does not want to relocate the kitchen.
In accordance with the Town's standards for secondary units, the main and
secondary units are required to be architecturally consistent (see Attachment 3
for secondary unit standards). The main house is primarily stucco and the
existing cottage is primarily wood siding. The Planning Commission may want
to consider offering direction to the applicant concerning the consistency of the
architectural styles of the two buildings.
The new primary residence will be two stories with the second floor covering the
entire first floor with the exception of the garage area. The proposed second
story is not set back from the first floor walls. In the past, the Planning
Commission has requested that a second story be set in from the first story to
help reduce the massing and improve the architectural style of the building. The
second story does not extend above the garage area but extends directly above
the remaining walls of the first floor. There is ample area remaining on the
property for future additions.
. Planning Commission
February 8, 1995
Lands of Hong
Page 3
The driveway to the property branches off along both property lines. The
existing gravel driveway extends towards the cottage and the additional parking
space for the cottage. A new driveway is proposed to extend along the southern
property line to the new four car garage. The applicant have been informed that
excessive paving is not recommended within the setbacks. Staff requests that the
Commission discuss this design with the applicant and direct them accordingly.
Since the building is located adjacent to the freeway, a traffic noise study was
provided by the applicant (see Attachment 4). The noise levels both on the
exterior and interior of the house are 10 dB in excess of Town standards. Thus
mitigation measures are required for the house in the way of construction
materials for noise attenuation. The interior noise levels are to be mitigated
through Sound Transmission Class (STC) 30 windows and doors on the second
floor and STC 25 on the first floor. The report states that the windows and doors
which face the freeway should remain closed at all times.
Noise walls are recommended to mitigate the freeway noise on the exterior of the
proposed house. These walls are 14 feet in height and extend along the property
line which abuts the freeway as well as 150 feet along the southern property line
and 250 feet along the northern property line. These walls will lower the noise
level to 60 dB CNEL to meet Town standards,yet their height and location do not
comply with the Town's guidelines. Staff recommends that the applicant
investigate other options for noise mitigation with the noise consultant, such as
the use of a birm,plantings,relocation of the residence or shorter walls or a
combination of these to meet Town standards. Another alternative is to reorient
the house so that the proposed outdoor living area is not as open to the freeway.
The Fire Department reviewed the plans and has no recommended conditions.
The Pathways Committee visited the site and no request was made. The
Environmental Design Committee evaluated the project and suggested that the
house be redesigned to include eaves,balconies or a trellis to provide some type
of outdoor shading on the property. Tall plantings were recommended for the
property line abutting the freeway to mitigate the noise and view of the freeway.
Staff is available to answer any questions from the Commission or any member
of the community.
ATTACHMENTS:
1. Development plans: site plan,section and elevations (two pages)
2. Letter to applicant from Staff, dated March 3, 1982;
3. Secondary Unit Standards;
Planning Commission
February 8, 1995
Lands of Hong
Page 4
4. Traffic Noise Assessment Study.
cc: Stanley and Helen Hong
26370 Ginny Lane
Los Altos Hills, CA 94022
Dick Fang
21726 Noonan Court
Cupertino,CA 95014
Planning Commission
February 8, 1995
Lands of Hong
Page 5
ATTACHMENT 1
RECOMMENDED CONDITIONS FOR SITE DEVELOPMENT PERMIT FOR
NEW RESIDENCE AND SECOND UNIT
HONG - 26370 GINNY LANE
A. PLANNING DEPARTMENT:
1. Any changes or modifications to the approved plans shall be
approved by the Planning Director or the Planning Commission,
depending on the scope of the changes.
2. Prior to final inspection a landscape planting plan shal be reviewed
by the Site Development Comittee. Particular attention shall be
given to plantings which will be adequate to break up the view of
the new residence from surrounding properties and from Highway
280. A cash deposit and/or landscape maintenance agreement may
be required to assure that the appproved landscaping is planted
and maintained. Outdoor lighting shall be reviewed and approved
with the landscape plan.
3. Two copies of a grading and construction operation plan shall be
submitted by the property owner for review and approval by the
City Engineer and Planning Director prior to acceptance of plans for
building plan check. The grading/construction operation plan shall
address truck traffic issues regarding dust,noise, and vehicular and
pedestrian traffic safety on Ginny Lane,Purissima Road and other
roadways in the area;storage of construction materials; placement
of sanitary facilities; clean-up area (see Engineering Department for
specifications);parking for construction vehicles; and parking for
construction personnel. A debris box (trash dumpster), shall be
placed on site for collection of construction debris. Arrangements
must be made with the Los Altos Garbage Company for the debris
box,since they have a franchise with the Town and no other hauler
is allowed within the Town limits.
4. The property owner shall inform the Town of any damage and
shall repair any damage caused by the construction of the project to
pathways,private driveways,public and private roadways prior to
final inspection and release of occupancy permits and shall provide
the Town with photographs of the existing conditions of the
roadways and pathways
Planning Commission
February 8, 1995
Lands of Hong
Page 6
5. Paint colors shall be chosen by the applicant and approved by staff
in conformance with the Town's adopted color board. A color
sample shall be submitted to the Planning Director for approval
prior to painting of the exterior of the residence.
6. Fire retardant roofing is required for the new residence.
7. Any skylights shall be designed to reduce emitted light and no
lighting shall be placed in skylight wells.
8. Upon completion of construction, a final inspection shall be set
with the Planning Department and Engineering Department at least
two weeks prior to final building inspection approval.
9. The existing 460 square foot shed located along the northwestern
property line must be removed from its current location in the side
yard setck. If it is proposed to be relocated on site, a revised site
plan shall be submitted for review and approval by the Planning
Director prior to acceptance of plans for building plan check.
B. ENGINEERING DEPARTMENT:
10. The site drainage associated with the proposed development must
be designed as surface flow wherever possible to avoid
concentration of the runoff. The proposed drainage shall be
designed to maintain the existing flow patterns and shall be
approved by the Engineering Department prior to acceptance of plans
for building plan checked. Final drainage shall be inspected by the
Engineering Department and any deficiencies corrected to the
satisfaction of the Engineering Department prior to final approval.
11. The preliminary grading plan shall be revised to reflect the
approved site development design and shall be approved by the
Engineering Department prior to acceptance of plans for building plan
check. Any and all changes to the approved grading and drainage
shall first be approved by the Town Engineering Department. No
grading shall take place during the grading moratorium
(November 1 to April 1) without prior approval from the Town
Engineering Department. No grading is permitted within ten feet
of any property lines except for the driveway connection to Ginny
Lane.
• Planning Commission
February 8, 1995
Lands of Hong
Page 7
12. An erosion and sediment control plan shall be submitted for review
and approval by the Engineering Department prior to acceptance of
plans for building plan check. The contractor and the property owner
shall comply with all appropriate requirements of the Town's
NPDES permit relative to grading and erosion / sediment control.
Any areas on the site that have the native soil disturbed shall be
protected for erosion controlduring the rainy season and shall be
replanted prior to final approval.
13. Ginny Lane shall be kept clean and free of mud-tracking during the
construction of this project. All affected streets shall be cleaned by
the end of each work day.
14. The existing Ginny Lane right of way as located on Lot No. 1 of
Tract No.3328 shall be dedicated as public right of way. A legal
description and plat map shall be submitted to and approved by
the Engineering Department so that the Town may prepare the
dedication document. The signed and notarized dedication
document shall be returned to the Town for recordation prior to
acceptance of plans for building plan check.
15. All public utility services shall be undergrounded.
16. Properties residing within the Los Altos School District
boundaries must pay School District fees before receiving their
building permit from Los Altos Hills.. The applicant must take a
copy of Worksheet #2 to both the elementary and high school
district offices, pay theappropriate fees and provide the Town
with a copy of their receipts.
CONDITION NUMBERS 3,9,10,11,12,14 AND 16 SHALL BE COMPLETED
AND SIGNED OFF BY THE PLANNING DIRECTOR AND THE CITY
ENGINEER PRIOR TO ACCEPTANCE OF CONSTRUCTION PLANS FOR
PLAN CHECK BY THE BUILDING DEPARTMENT. ALL OTHER
CONDITIONS MUST BE SATISFIED PRIOR TO FINAL INSPECTION.
NOTE: The Site Development permit is valid for one year from the approval
date (until February 8, 1996). All required building permits must be obtained
within that year and work on items not requiring a building permit shall be
commenced within one year and completed within two years.
4k,.
,14-44
4c4k\:.
•
"~ , r•1 uONi i•OAU •U• ALTO) HILLS CALi•ORNIA 9AU3f U
4:....L°#'/"Pdf:a 4I„4,4A-C k
D4
1 7117 ' i�. jf'
:I'V'',i'
,�;•V
[J ,),
S
MA';','
1r,+.;tom.+;k,
L"";r
Citi
T 4..x,#.i.
'*ti r
March 5, 1982 ;; ,
Mr. Glen R. Williams : r•'
26370 Gi nny Lane '` •r:*`fr.
Los Altos Hills, CA 94022 " `u
Re: Parcel 182-06-037 _ `n;
Assessor # 3874668 •• •,.:
Dear Mr. Williams: '
We have received your application for the storage shed on your i+r...,:t}
property. You have .indicated on the site plan that the building ,i'�-.`
is 16'0" x 24'0", and is now located 12'0" from the north east. T;y
property line.
lie cannot issue a permit for this storage shed structure, for you
must have 30'0" from the property line to the structure. `"`' -it'
The structure is in violation in two ways. One violation exists ;. .:W:
for the construction prior to obtaining a permit. And two. the ',r 1'` ``
building is now sitting only 12'0" from the property line.
Therefore, before we can issue a proper permit, you must move =-',•
s
the storage shed 30'0" from the property line. Then you can up- ;•,. -"
date your site plan and a permit can be issued. : ,z(
We ask for your cooperation and trustyou will conform to the .1
regulations immediately. ', -gip
Thank you and for your views are copies of the involved sections "' '
of the Los Altos Hills Municipal Code which has been violated. ' ``a
cer ]y, ac
1 I f. ,In:
s p
)eward L. Murphy •%
Building Official
c.c. City Attorney jsl., '
County Assessor • ``_
•
•
,'';p ,, F ..t.' •• .4'� a i ':':.'::...;e',..'
., ,< 4y ;'e-'H-..4.V.,•'::1�:i .`:.;k.....,..".v.,. - 't .7. ••• 4y ? J } - ` . .. .
f2e . ., -a � . . . ^ � , ;. ^ .�,� J4? ., 3 ,a- - .." .•'''''''"I'..11"-• \ ita "Gr { . T'�t' ' _ ..;,h-ilk.
',-
•
1, 3 J_ p� J ]e' t"` 4 • r_ a
,= g * • }t r'8 ct, gr. * .. 7 r
•mollimilo4 • ILIMOMMIMMINIiIMII
• 7
tx.'s T I-Pa 9
Si
1 STRO cT4Iat "'
• . . i
I
a •
l .
V * . o • Hous € .
V otb
.
•
- .--
s Q 4111.1.
_
. so'
•
_ , s,
•
10111111 ... r `
at{..a stR�eTke ._.1__. 6 . , . •
-
.,
GLe0 --71'"...°a'---...... .---‘ r- r '
r A c 1 •76 G Pi Ail b.' ii1*-gill-3t: . I "or I r
1.o., A(ToS •trills , N•/ ,
i � _:
____________,___________ __________ 1
. ...._
§ 10-1.702 LOS ALTOS HILLS MUNICIPAL CODE § 10-1.702
- (d) Accessory buildings. Accessory buildings may be constructed
only in accordance with the setback requirements of this chapter. An
accessory building may be erected prior to the construction of the main
building only if it is agreed that the main building shall be completed
within three (3) years from the date of the issuance of the permit for the
accessory building. A temporary accessory building shall be removed
within thirty (30) days after.the completion of the main building or
••�.�;• within eighteen (18) months after the issuance of a permit for the
,••••••,... •,; :;. , accessory building, whichever is the earlier date.
'=,. (e) Private stables. A maximum of two (2) hoofed animals per
f� ' %`� ? . acre shall be permitted provided one additional hoofed animal may be kept
• on each additional one-half(1/2) acre, or fraction thereof, and provided,
further, the conditions are satisfactory to the County Department of
,',. .w - Health or such other agency as may be in charge of health standards for
,- •i ;1••;ei:••: the Town.
i.;' (f) Swimming pools, tennis courts, greenhouses, and workshops.
.Y workshops, and other
Swimming pools, tennis courts, greenhouses, and
.•<• •,;', accessory uses found by the Planning Commission to comply with the
..;..•._ .,.•'
•
s :.�; ; definition of accessory use, shall be permitted.
(g) Small family day care homes. Small family day care homes
' `••
••:`.:-::".';•••`••.• which provide care, protection and supervision of six (6)or fewer children
^:.:•. . (including children under the age of ten (10) years who reside at the home)
'.:;:• ' ....•.M1 = in the provider's own home, for periods of less than :twenty-four (24)
•�}h�':--,- hours per day, while the parents or guardians are away, pursuant to State
•.;.• !
`• 4;=_ ‘1.S1 11regulations shall be permitted. No business license fee or tax shall be
imposed on a small family day care home.
_':;X (h) Household pets and domestic animals. Household pets and
.. '::�,�A�"''''`' ' domestic animals as permitted by Town regulations may be kept.
-; ..,-,,,, garden structures,(i) Ornamental garden structures. Ornamental
"•,- '• such as benches, statuary, raised planters and fountains, shall be
_ .
( . •_
,_?r permitted.
Antennas and dish antennas. Antennas and dish antennas are
4 ''"' ' (j) requirements set forth in Article 5 of Chapter 1
ti?~'=
M ,
§ 10-1.702 LOS ALTOS HILLS MUNICIPAL CODE § 10-1.703
(3) If the secondary dwelling is within or attached to the
primary dwelling, it shall be constructed so that the entire structure
appears to be one (1)dwelling.
(4) If the secondary dwelling is separate from the primary
•
•
dwelling, it shall not be sited in a visually prominent location, and shall
respect the visual and acoustic privacy of primary dwellings on
•
contiguous lots.
(5) The lot on which a secondary dwelling is located must
'... :.. be connected to the public sanitary sewer system or have a private sewage
disposal system that is deemed to be adequate for the addition of the
•'• ;: �: ;�'.: second dwelling by the Santa Clara County Division of Health Services;
and must have an adequate water supply.
(6) The secondary dwelling shall not have a significant
_ . adverse impact on traffic flow and safety.
(7) Any vehicular access to a secondary dwelling shall be by
-•• a common driveway with the primary dwelling.
• (8) The views of prominent scenic features by primary
dwellings on contiguous lots shall be preserved.
(I) Temporary trailer coaches. Trailer coaches during construction
or substantial remodeling of a primary dwelling are permitted, subject to
receipt of a zoning permit, pursuant to Section 10-1.310, after a public
hearing held by the Zoning Administrator pursuant to Section 10-1.1105.
One (1) trailer coach specifically designed and equipped for human
' .• '- habitation may be placed on a lot, in accordance with the setback
requirements of this Code and occupied only by the owner of the lot and
members of the owner's family, as a temporary residence during
•
construction or substantial remodeling of the primary dwelling on the lot.
This permit shall be granted for no more than six (6) months, but shall
• be renewable upon the determination of the Zoning Administrator that the,
• use has not resulted in detriment or nuisance to the adjacent properties or
the neighborhood. However, in all cases, the trailer coach shall be
Y removed prior to building permit final.
(§ 1, Ord. 305, eff. October 3, 1986; § 1, Ord. 319, eff. April 1, (R)
" ' • '':'" 1989• § 3, Ord. 3: 4, eff. July 20,
;-• ; _; 1987; § 3, Ord. 329, eff. October 20, ,
1990; § 1, Ord. 358, eff. December 4, 1993)
•
4.144'40:4i - Sec. 10-1.703. Conditional uses and structures (R-A).
The following uses may be established in the Residential-
Agricultural District subject to the approval of the Planning
•
• • . • ' ' • Commission, and the issuance of a permit thereof pursuant to the
•
. • • . - provisions of this chapter:
(a) Public libraries;
(Los Altos Hills 12-15-93)
i n-D r
EDWARD L. PACK ASSOCIATES, INC.
1030 E. DUANE AVENUE,SUITE F Acoustical Consultants TEL: 408.730.5574
SUNNYVALE,CA 94036 FAX: 408.730.0702
. September 19, 1994
Project No. 26-076
Mr. Stanley T-Iong
25370 Ginney Lane
Los Altos Hills, CA 94022
Subject: Traffic Noise Assessment Study for the Planned Single-Family
Residence, 26370 Ginney Lane, Los Altos Hills
Dear Mr. Ilong:
This report presents the results. of a traffic noise assessment study for the planned
single-family residential development at 26370 Ginney Lane in Los Altos Hills. The
noise levels presented herein were evaluated against the standards of the Town of
Los Altos Hills Noise Element, Ref. (a). An analysis of the on site noise
measurements indicates that the primary source of noise at the site is traffic on
• Interstate 260.
Section I and II of this report contain a summary of our findings and
recommendations, respectively. Subsequent sections contain site traffic and project
descriptions, analyses, evaluations and conclusions. Appendices A, B and C,
attached, contain the list of references, descriptions of the standards,definitions of
the terminology, acoustical instrumentation used for the field survey, ventilation
requirements, general building shell controls and tl:: noise measurement data.
ME tom'R A, ;UM CAI.SciCIF rV OF AMFRICA AUDIO FNGINEI"RING SOCIF.rY
- 2 -
I. Findings
The findings presented below were evaluated against the standards of the
Town of Los Altos Hills Noise Element, which specifies a noise limit of 60 dBA for
residential land-use. However, the Town of Los Altos Hills Planning Department
has directed Edward L. Pack Associates, Inc., to use the Community Noise
Equivalent Level (CNEL) noise descriptor, Ref. (b). The Town considers 60 dB
CNEL as acceptable for residential exterior areas. Residential interiors are limited
to 45 dB CNEL.
The noise levels shown below are without the application of mitigation
measures and represent the noise environment for the existing site.
A. Exterior Noise Levels
The existing noise exposure at the planned minimum building
setback from 1-280 (approximately 175 ft. from the centerline
of the road) is 68 dB CNEL. Under future traffic conditions,
the noise exposure will increase to 70 dB CNEL. Thus, the
noise exposures will be up to 10 dB in excess of the standards.
B. Interior Noise Levels
In the most impacted living spaces of the residence, the
interior noise exposures will be 53 and 55 dB CNEL under
existing and future traffic conditions, respectively. Thus, the
interior noise exposures will be up to 10 dB in excess of the
Town of Los Altos Hills Noise Element standards.
As noise excesses occur at the site, mitigation measures will be required.
The recommended measures are described in Section II, below.
- 3 -
II. Recommendations
To achieve compliance with the standards, mitigation measures for exterior
and interior areas are required.
A. Exterior Noise Control
To comply with the 60 dB CNEL noise exposure limit of the standards, the
following property line noise control barrier is required:
Construct a 14 ft. high acoustically-effective barrier along the
property line contiguous with the I-280 right-of-way. To reduce
flanking noise, the barrier must continue along the side
property lines for distances of 150 ft. on the south side and 250
ft. on the north side.
To reduce the noise exposures in the rear and side yards to 65 dB CNEL, the
following noise control barrier is required.
Construct a 10 ft. high acoustically-effective barrier along the
property line contiguous with the I-280 right-of-way. To reduce
flanking noise, the barrier must continue along the side
property lines for distances of 150 ft. on the south side and 250
ft. on the north side.-
The barrier heights are in reference to the nearest building pad elevation.
•
- 4 -
To achieve an acoustically-effective barrier or fence,it must be made air-
tight, i.e., without cracks, gaps, or other openings, and provide for long-term
durability. The property line barrier can be constructed of wood, concrete, stucco,
masonry, earth berm or a combination thereof, and must have a minimum surface
weight of 2.5 lbs. per sq. ft. If a wood fence is used, homogeneous sheet material are
. preferable to conventional wood fencing because of the tendency of the latter to
warp and form openings with age. However, high quality, air-tight, tongue-and-
groove, shiplap, or board and batten construction can be used provided the
minimum surface weightrequirement is met and the construction is air-tight. The
noise control barrier must be constructed so that all joints, including connections
with posts or pilasters, are sealed air-tight and no openings are permitted between
the barrier and the ground.
Please note that the flanking barrier segments may be eliminated if the main
barrier can be incorporated into similar barriers at the adjacent properties. For
instance, a 10 ft. (approx.) high continuous earthen berm along the freeway at the
properties adjacent to the freeway would reduce I-280 traffic noise to approximately
65 dB CNEL at those properties.
B. Interior Noise Control
To achieve acceptable interior noise exposures, the following window
controls will be required:
With the implementation of the 14 ft. high barrier, maintain
closed at all times all second floor windows and sliding glass
• doors that have a direct or side view of 1-280. Install window
and door assemblies rated minimum Sound Transmission Class
30.
- 5 -
With the implementation of the 10 ft. high barrier, maintain closed at all
times all first floor windows and sliding glass doors that have a direct or side view of
the freeway. Install window and door assemblies rated minimum Sound
Transmission Class 25. At second floor living spaces with a direct or side view of the
freeway, maintain windows and doors closed. These windows and doors shall be
rated minimum STC 30.
To achieve an acoustically-effective window and door construction, the
moveable window panels must form an air-tight seal when in the closed position. In
addition, the windows and door frames should be of a good quality, with tight seals
and the window frames must be caulked to the wall openings with a non-hardening
caulking compound to prevent sound infiltration.
All remaining windows of the project and all bathroom windows may be
fitted with any type of glass and may be kept open as desired.
When windows are maintained closed for noise control, they are to be
operable, as the requirement does not imply a fixed condition. Also, under the
closed window requirement, some form of mechanical ventilation should be
provided to assure a habitable environment, as specified by the Uniform Building
Code (UBC) and as described in Appendix B.
•
III. Site,Traffic and Project Descriptions
The planned development site is located on the east side of I-280 in Los
Altos Hills. The site is relatively flat with a slight upgrade towards freeway. The I-
280 northbound lanes are approximately 3 ft. above the site, while the southbound
lanes are approximately 8 ft. above the site. A single-family home is presently
situated on the site with several associated out-buildings.
•
- 6 -
The noise environment is controlled by traffic sources on I-280 which carries
an Average Daily Traffic (ADT) of 91,00 vehicles, Ref. (c). Although future traffic
volumes are not available from CalTrans a the time of this writing, information from
CalTrans engineers indicates that traffic is typically projected to increase by 3% per
year. Therefore, for future year 2014, the I-280 traffic volumes are estimated to
increase to 164,356 ADT.
The planned project includes the construction of one single-family residence.
Ingress and egress will be by of Ginney Lane.
IV. Analyses, Evaluations and Conclusions
A. Exterior Noise Levels
To determine the existing noise levels at the site, noise measurements were
made for a continuous 24-hour period from September 12-13, 1994 at a location 135
ft. from the I-280 property line. This location corresponds to the nearest building
setback from the freeway. The noise levels were recorded and processed by a
Larson-davis Model 700 Precision Integrating Sound Levels Meter, which yielded by
direct readout a series of descriptors of the sound levels versus time. The results of
the recordings are shown in the data table in Appendix C. The table includes the
maximum and minimum levels, and the levels exceeded 1%, 10%, 50% and 90% of
the time. Also included is the equivalent-energy level (Leq) which is used to
calculate the CNEL.
As shown in the table, the Leg's ranged from 60.5 to 70.5 dBA during. the
daytime and 50 to 68 dBA during the nighttime recording periods.
- 7 -
Vehicular traffic noise contains a wide spectrum of frequency components
(from 100 to 10,000 Hertz), which is associated with engine, tire, drive-train, and
other sources. The frequency components are centered primarily in the 250 and 500
-Hz octave bands and were used in determining the noise control measures
recommended for this project.
V. Evaluation of the Traffic Noise Levels
A. Exterior Noise Exposures
The CNEL was calculated by decibel averaging the measured Leg values for
the daily time periods of the CNEL index using the mathematical formula shown in
Appendix B. The results of the calculations indicate that the exterior noise
exposure is 58 dB CNEL at the planned minimum building setback from I-280.
Under future traffic conditions, the noise exposure will increase to 70 dB CNEL.
Thus, the noise exposures will be up to 10 dB in excess of the Town of Los Altos
Hills standard.
B. Interior Noise Exposures
To evaluate the interior noise levels against the 45 dB CNEL interior limit of
the Town of Los Altos Hills Noise Element standards, a 15 dB reduction was
applied to the exterior levels to account for the attenuation provided by the building
shell under annual average conditions. The annual average condition assumes that
windows with single-strength glass are maintained open 50% of the time for natural
ventilation. Thus, in the most impacted living spaces, the interior noise exposures
will be 53 and 55 dB CNEL under existing and future traffic conditions, respectively.
These levels are up to 10 dB in excess of the interior limits of the Town of Los Altos
Hills Noise Element.
- 8 -
As noise excesses occur at exterior and interior areas, mitigation measures
will be required. The recommended measures are described in Section II.
The study findings and recommendations for present conditions are based on field
measurements and other data and are correct to the best of our knowledge.
However, significant changes in future traffic volumes, vehicle speeds, motor vehicle
technology or other future changes beyond our control may produce long-range
noise results different from our estimates.
If you have any questions or require additional information, please call me.
Sincerely,
EDWARD L. PACK ASSOC., INC.
G �
'etrre
President
JKP:j
Attachment: Appendices A, B and C
APPENDIX A
References:
a) Noise Element of the General Plan, Town of Los Altos Hills,
b) Information on the Town of Los _Altos Hills Noise Element Standards
Provided by Ms. Linda Niles, Town of Los Altos Hills Planning Department,
by Telecon to Edward L. Pack Associates, Inc., September 22, 1994
c) 1993 Traffic Volumes of California State Highways, State of California
Department of Transportation, Division of Traffic Operations, July 1994
APPENDIX B
Noise Standards, Terminology, Instrumentation,
Ventilation, and Building Shell Requirements
1. Noise Standards
A. Town of Los Altos Hills Noise Element Standards
•
The Town of Los Altos Hills has verbally specified a noise level limit of 60
dB Community Noise Equivalent Level (CNEL) for exterior locations of residential -
areas. An interior limit of 45 dB CNEL has been specified for living spaces.
B-1
2. Terminology
A. Statistical Noise Levels
Due to the fluctuating character of urban traffic noise, statistical procedures
are needed to provide an adequate description of the environment. A series of
statistical descriptors have been developed which represent the noise levels
exceeded a given percentage of the time. These descriptors are obtained by direct
readout of the Community Noise Analyzer. Some of the statistical levels used to
describe community noise are defined as follows:
L10 - A noise level exceeded for 10% of the time, considered to be an
"intrusive" level.
L50 - The noise level exceeded 50% of the time representing an
"average" sound level.
L90 - The noise level exceeded 90 % of the time, designated as a
"background" noise level.
Leq - The continuous-equivalent level is that level of a steady noise
having the same energy as a given time-varying noise. The Leg thus
represents the decibel level of the time-averaged,value of sound
energy or sound pressure squared. The Leq is the noise descriptor
used to calculate the DNL and CNEL descriptors.
•
B-2
B. Community Noise Equivalent Level (CNEL)
The CNEL is a measure of the cumulative noise exposure over a 24 hour
period. The CNEL index divides the 24 hour day into three subperiods, i.e., the
daytime (7:00 am to 7:00 pm), the evening period (7:00 pm to 10:00 pm), and the
nighttime period (10:00 pm to 7:00 am). Also, weighting factors of 5 and 10 dBA
are applied to the evening and nighttime periods, respectively, to account for the
greater sensitivity of people to noise during those periods. The CNEL values are
calculated from the measured Leq values in accordance with the following
mathematical formula:
CNEL = [(Ld+101og1012) & (Le+5+ 101og103) & (Ln+10+101og109)] - .101og1024
where:
Ld = Leq for the daytime (7:00 a.m. to 7:00 p.m.)
Le = Leq for the evening (7:00 p.m. to 10:00 p.m.)
Ln = Leq for the nighttime (10:00 p.m. to 7:00 a.m.)
24 indicates the 24 hour period
& denotes decibel addition
B-3
C. A-Weighted Sound Level
The decibel measure of the sound level utilizing the "A" weighted network of
a sound level meter is referred to as "dBA". The "A" weighting is the accepted
standard weighting system used when noise is measured and recorded for the
purpose of determining total noise levels and conducting statistical analyses of the
environment so that the output correlates well with the response of the human ear.
3. Instrumentation
The on-site field measurement data were acquired by the use of a Larson-
Davis Model 700 Precision Integrating Sound Level Meter, which provides a direct
readout of the L exceedance statistical levels including the equivalent-energy level
(Leg). The Model 700 meter was factory modified to meet Type 1 performance,
conforming with ANSI S1.4. Input to the meter was provided by a microphone
extended to a height of 5 ft. above the ground. The "A" weighting network and the
"Fast" response setting of the meter were used in conformance with the applicable
standards. All instrumentation was acoustically calibrated before and after field
tests to assure accuracy.
B-4
4. Ventilation Requirements
Ventilation requirements to be applied when windows are maintained closed
for noise control are specified in the Uniform Building Code (UBC), 1985 edition,
Section 1205 as follows:
"In lieu of required exterior openings for natural ventilation, a
mechanical ventilating system may be provided, Such system
shall be capable of providing two air changes per hour in all
guest rooms, dormitories, habitable rooms, and in public
corridors. One-fifth of the air supply shall be taken from the
outside".
Based on our previous experience, a "summer switch" on the furnace fan is
normally considered acceptable as a ventilation system by FHA and other agencies.
Air-conditioning is also an acceptable system.
B-5
5. Building Shell Controls
The following additional precautionary measures are required to assure the
greatest potential for exterior-to-interior noise attenuation by the recommended
mitigation measures. These measures apply at those units where closed windows
are required:
Unshielded entry doors having a direct or side orientation
toward the primary noise source must be 1-5/8" or 1-3/4" thick,
insulated metal or solid-core wood construction with effective
weather seals around the full perimeter. Mail slots should not
be used in these doors or in the wall of a living space, as a
significant noise leakage can occur through them.
If any penetrations in the building shell are required for vents,
piping, conduit, etc., sound leakage around these penetrations
can be controlled by sealing all cracks and clearance spaces
with a non-hardening caulking compound.
Fireplaces should be provided with tight-fitting dampers.
B-6
f
STANLEY HONG
FILE: 26-076.DTA
9/12-13/94
26370 GINNEY LANE
LOS ALTOS HILLS
135 ' FROM I-280 PROPERTY LINE
LARSON-DAVIS LABS -- MODEL 700 SN 700B3183
Detc FAST Wght A
Cnt LVL SEL Lmax Lpk Lmin Date Time Dur Ex Pk Ov
1 65.5 101.5 72 . 5 83 . 5 56. 5 12 SEP 16: 09 : 13 1: 00 h:m 1 0 0
LO1 = 70. 0 L10 = 68. 5 L50 = 65. 0 L90 = 61.5
2 66.5 102 . 0 73 . 0 85. 0 56.0 12 SEP 17 : 09: 13. 1:00 h:m 0 0 0
LO1 = 70. 5 L10 = 68.5 L50 = 66. 5 L90 = 63 . 0
3 66. 0 101.5 86. 0 95. 5 53 . 0 12 SEP 18: 09 : 13 1: 00 h:m 0 0 0
L01 = 70. 5 L10 = 68. 5 L50 = 65. 5 L90 = 61. 5
4 63 . 5 99. 0 73 . 0 87. 5 44 . 0 1. 2 SEP 19 : 09 : 13 1: 00 h:m 0 0 0
LO1 = 69. 0 L10 = 66. 5 L50 = 63 . 0 L90 = 58 . 0
5 61.0 96. 5 71. 0 82 . 5 45.5 12 SEP 20: 09 : 13 1: 00 h:m 0 0 0
LO1 = 66. 5 L10 = 64 . 0 L50 = 60. 0 L90 = 54 . 0
6 61.5 97 . 0 70. 0 82 . 5 46. 5 12 SEP 21: 09 : 13 1: 00 h:m 0 0 0
LO1 = 67 . 5 L10 = 64 . 5 L50 = 60.5 L90 = 54 . 0
7 59. 0 94 . 5 69. 5 80. 0 44 . 5 12 SEP 22 : 09 : 13 1: 00 h:m 0 0 0
L01 = 66. 0 L10 = 63 .0 L50 = 57. 0 L90 = 50. 0
8 57. 0 92 . 5 70. 5 84 . 0 39.5 12 SEP 23 : 09 : 13 1: 00 h:m 0 0 0
LO1 = 66. 0 L10 = 61. 0 L50 = 52 . 5 L90 = 46. 5
9 54. 5 90. 0 67 .5 80. 5 34 . 5 13 SEP 0: 09: 13 1: 00 h:m 0 0 0
LO1 = 64 . 0 ' L10 = 59. 0 L50 = 49 . 0 L90 = 43 . 0
10 51. 0 86.5 70. 0 79. 5 30. 0 13 SEP 1: 09: 13 1: 00 h:m 99 0 0
LO1 = 62 . 0 L10 = 55. 0 L50 = 44. 5 L90 = 35. 5
11 50. 0 85. 5 70. 5 83 .5 30. 0 13 SEP 2 : 09: 13 1: 00 h:m 99 0 0
LO1 = 63 . 0 L10 = 52 . 0 L50 = 37. 0 L90 = 32 . 0
12 51.5 87. 0 71. 0 84 . 0 28 .5 13 SEP 3 : 09 : 13 1: 00 h:m 99 0 0
L01 = 65. 0 L10 = 54 . 5 L50 = 38 . 5 L90 = 31. 0
13 54.5 90. 0 72 . 0 82 . 5 29 .5 13 SEP 4 : 09: 13 1: 00 h:m 99 0 0
LO1 = 65. 0 L10 = 59 . 5 L50 = 45. 0 L90 = 34 .0
14 62 .5 98. 0 71.5 82 . 5 39. 0 13 SEP 5: 09 : 14 1: 00 h:m 0 0 0
L01 = 69. 0 L10 = 66. 0 L50 = 60. 5 L90 = 48 . 5
15 68 . 0 103 . 5 74 . 5 91 . 5 50 . 0 13 SEP 6: 09 : 14 1: 00 h:m 0 0 0
LO1 = 72 . 5 L10 = 70 . 5 L5.0 = 67 . 5 LOO = 63 . 0
16 70. 5 106 . 0 78 . 5 91 . 0 56. 0 13 SEP 7 : 09 : 14 1: 00 h:m 0 0 0
LO1 = 74 . 0 L10 = 72 . 0 L50 = 70. 0 L90 = 67 . 5
17 67 . 0 102 . 5 73 . 0 86 . 5 55. 0 13 SEP 8 : 09 : 14 1: 00 h:m 0 0 0
LO1 = 70 . 5 L10 = 69. 0 L50 = 66 . 5 L90 = 63 . 5
18 63 . 5 99 . 0 72 . 5 84 . 5 47 . 5 13 SEP 9 : 09 : 14 1: 00 h:m 0 0 0
LO1 = 68 . 5 L10 = 66. 0 L50 = 62 . 5 L90 = 58. 5
19 61. 5 97 . 0 71. 5 84 . 5 45. 0 13 SEP 10: 09 : 14 1: 00 h:m 0 0 0
LO1 = 67 . 5 L10 = 64 . 0 L50 = 60. 5 L90 = 55. 5
20 61. 0 96. 5 72 . 5 83 . 0 49 . 0 13 SEP 11: 09: 14 1: 00 h:m 0 0 0
LO1 = 67 . 0 L10 = 64 . 0 L50 = 60. 5 L90 = 56. 0
21 60. 5 96. 5 69 . 5 85 . 0 49 . 0 13 SEP 12 : 09 : 14 1: 00 h:m 0 0 0
L01 = 67 . 0 L10 = 63 . 5 L50 = 59 . 5 L90 = 55. 5
22 61. 0 96 . 5 72 . 0 83 . 0 45 . 0 13 SEP 13 : 09 : 14 1: 00 h:m 0 0 0
LO1 = 67 . 0 L10 = 64 . 0 L50 = 60. 0 L90 = 55. 5
23 60. 5 96. 0 71. 5 87 . 5 48 . 0 13 SEP 14 : 09 : 14 1: 00 h:m 0 0 0
LO1 = 66. 0 L10 = 63 . 0 L50 = 59 . 5 L90 55. 5
24 60. 5 96 . 0 70. 0 84 . 5 48 . 5 13 SEP 15 : 09 : 14 1: 00 h:m 0 0 0
LO1 = 65. 5 L10 = 63 . 0 L50 = 59 . 5 L90 = 56. 5