HomeMy WebLinkAboutDRB 2019-03-19 #3SAN RAFAE L
THE CITY WITH A MISSION
Community Development Department — Planning
Division
Meeting Date: March 19, 2019
Case Numbers: ED18-046 & ADU18-033
Project Planner: Alan Montes 415.485.3397
Agenda Item:
REPORT TO DESIGN REVIEW BOARD
SUBJECT: Vacant Flag Lot Located behind 1450 Grand Avenue (Tentative Address 1446 Grand
Avenue) — Request for an Environmental and Design Review Permit to allow the construction
of a new two-story, 4,049 sq. ft., single family residence (including garage) on a flag lot and to
convert the existing shed on the property into an accessory dwelling unit (ADU); APN: 015-
201-39; Single Family Residential (R10) District; Bob Porter, Applicant/Owner; Dominican
Neighborhood.
PROPERTY FACTS
Location
General Plan Designation
Zoning Designation Existing Land -Use
Project
LDR
R10
Vacant
Site:
10'
Rear.
10'
North:
LDR
R10
Single -Family Residence
South:
LDR
R10
Single -Family Residence
East:
LDR
R10
Single -Family Residence
West:
LDR
R10
Single -Family Residence
Lot Size*
Lot Coverage (Max.)*
Required:
10,000 sf
Standard: 5,004.8 sf (40%)
Existing:
12,512 sf ( 14,227 sf with
Proposed: 3,294 sf (26.3%)
panhandle)
Height**
Residential Density
Allowed:
30'
Allowed: 1 (ADU's do not
count against density)
Proposed:
27.1'
Proposed: 1
Parking
Required: 2 covered spaces
Proposed: 2 covered spaces
Min. Lot Width (New lots)
Required: 75'
Existing: 85'
Upper Floor Area
Allowed: 3,753.6 sf
Proposed: 1,334 sf
Setbacks
* The panhandle/pole portion of a lot that is primarily used and intended for access shall not be included in lot area for purposes of
development and application of development standards.
** Standard building height is measured from an established exterior finished grade elevation to mid -point of a sloped roof.
*** Creek Setbacks may be modify pursuant to section 14.16.080 — Creeks and other watercourses, discussed below.
Required
Proposed
Front:
20'
20'
Side(s):
10'
10'
Rear.
10'
45'
Creek
25'
15'
Setback***
* The panhandle/pole portion of a lot that is primarily used and intended for access shall not be included in lot area for purposes of
development and application of development standards.
** Standard building height is measured from an established exterior finished grade elevation to mid -point of a sloped roof.
*** Creek Setbacks may be modify pursuant to section 14.16.080 — Creeks and other watercourses, discussed below.
SUMMARY
The project is being referred to the Design Review Board (Board) for review of site and building design
for a new 4,049 sq. ft. single-family residence on a vacant flag lot. The project also includes the
conversion of an existing detached structure into an accessory dwelling unit (ADU). The project is
requesting a creek setback encroachment reduction along the southern portion of the property to meet
the turning requirements for the garage.
The Board's recommendation will be forwarded to the Zoning Administrator (ZA). Based on review of
the applicable design criteria, which is discussed in detail below, staff has concluded that the project
substantially conforms with the applicable criteria. However, Staff requests that the Board review this
report and provide a recommendation on compliance with all pertinent design criteria. Specifically, staff
asks the Board to consider the following:
Site Plan
• Whether the encroachment into the recommended creek setback is appropriate.
Materials and Colors
• Whether the materials and colors for the home are appropriate.
Landscaping
• Recommended species for the restoration of the creek -riparian zone.
BACKGROUND
Site Description & Setting:
The site is a vacant flag lot located behind 1450 Grand Ave. The site is currently developed with an
existing -483 sf shed located near --the north-east corner of the lot. On the eastern portion -of the lot there
is a creek running North -to South through the property.
History:
In 2004 a lot line adjustment occurred between 1450 and 1446 Grand Ave. (tentative address) which
ceded 2,218 sf from 1450 to 1446 Grand. No other applications have been filed on the subject site until
the current applications were requested.
The current application had a ZA hearing on February 20, 2019. During this hearing the project was
contentious among the adjacent neighbors. The primarily concerns were related to the erosion and
drainage. The applicant has submitted a Geotechnical Supplement on March 12, 2019, discussing the
revision to relocate the garage in the creek setback. The applicant is currently working on a storm water
control plan. The applicant is still working on the storm water control plan. When both plans are
completed submitted to the City they will be reviewed by the appropriate departments prior to
rescheduling the ZA hearing. Additional items that were brought up include the proposed creek
setback, shadowing, and size. These items are discussed below, in this report.
PROJECT DESCRIPTION
Use:
The project proposes to develop a new two-story, single-family residence and to convert a small
existing structure to an ADU. Both uses are permitted uses in the R10 zoning district.
Site Plan:
The project proposes to locate the residence in the center of the flag section of the lot, providing a 20'
front setback, a 15'-9" side setback on the north elevation, a 10' side setback on the south elevation,
and a 42-58' rear setback. There is a creek running along the rear property line extending 8' - 36' on
the subject property. The primary structure is requesting a creek setback encroachment to maintain a
2
minimum setback of 15', instead of 25', from the high bank of the creek along the southern portion of
the lot due to issues with the turning radius for the garage.
There's an existing 483 sf structure on the north-east portion of the lot that's proposed to be converted
into an ADU. This structure is located on the north side property line and is within the creek setback.
However, the state law governing ADU's is explicit in that an ADU is allowed within existing space,
including accessory structure even if the structure is nonconforming.
Architecture:
The single-family home is proposed to have hipped roofs and be cladded with Roseburg Breckenridge
wood veneer siding. The upper story has been stepped inwards to minimize the impacts on the
adjacent neighbors.
Landscaping:
The project proposes to plant and maintain several dozen trees along the perimeter of the property.
The plans indicate that the applicant has proposed to maintain the four (4) large redwood trees along
the north elevation of the site.
Drainage:
The plans include three (3) bioretention areas and two (2) swales. There are two (2) bioretention areas
located along the rear of the property and one (1) large bioretention area located along the front of the
property. The Department of Public Works (DPW) has reviewed the drainage plan and found it
appropriate for the size of the project. However, during the public hearing hosted on February 20, 2019
there was significant concern raised from the adjacent neighbors regarding the adequacy of the
drainage for the site. Staff has requested a full stormwater control plan, which is typically deferred to
the building permit stage, to be resubmitted to the City to confirm the adequacy of the. drainage. The
applicant is currently working on this plan.
ANALYSIS
General Plan 2020 Consistency:
The project is generally consistent with the General Plan. There are two policies that may affect the
design of the structure, LU -12 and CON -6. The project complies with Land Use Policy LU -12, Building
Heights, in that the midpoint of the roof is less than 30'. Conservation Policy CON -6, Creek and
Drainageway Setbacks, states that a 25 -foot setback should be maintained for all new development,
but also identifies that the City may waive this requirement for minor encroachments if it can be
demonstrated that the proposed setback adequately protects the function of the creek to the maximum
extent feasible. The City has reviewed the creek encroachment and associated Biological Assessment
and no City departments have identified an issue with the proposed encroachment.
Zoning Ordinance Consistency:
Chapter 4 - Base District
Use:
The single-family residence and ADU are permitted, by -right, in the R10 zoning district.
Development Standards:
The project complies with the development standards, by complying with the required setbacks,
maximum and maximum upper story requirements.
Chapter 16 — Site and Use Regulations
3
Section 14.16.080, Creeks and other watercourses, states that creek setbacks should be 25' or
greater from the high top of the creek bank, but shall be determined based on the following
criteria:
1. The setback provides for adequate maintenance, emergency vehicle access, adequate
debris flow avalanche corridors, flood control and protection from damage due to stream
bank undercutting;
2. The setback adequately protects and preserves native riparian and wildlife habitat;
3. The setback protects major view corridors and provides for recreation opportunities where
appropriate;
4. The setback permits provision of adequate and attractive natural landscaping.
The project originally proposed to comply with the setback. However, during the completeness
review DPW identified issues with the turning radius for the garage parking spaces. The applicant
worked with his civil engineers and DPW to try to resolve this issue. The resulting solution to
comply with the turning radius was to set the garage further back onto the property resulting in an
encroachment into the recommended 25' creek setback of up to 10'. Altogether the encroachment
would result in approximately 230 sq. ft. of encroachment into the creek setback. The applicant
provided a Biological Assessment (Exhibit 2; Creek -Riparian Zone Setback Report) supporting their
reduced creek setback. In summary, the Biological Assessment determined that the proposed
development, including the encroachment, will not significantly alter species use or use of habitat by
species from the current conditions, and that the location of the encroachment is stable and in no
danger of erosion or failure. The report also notes several recommendations, which should the
project be approved would be, incorporated as conditions of approval, including replacing the non-
native plants with native species, prohibiting outdoor lighting from shining directly into the creek,
and requiring a biological survey should construction occur during bird nesting season. DPW has
voiced support for the encroachment with the conditions that the proposal either remove existing
encroachments or improving .and maintaining the remainder of the creek setback area as riparian
habitat, instead of lawn area. No other City Departments have expressed concern regarding the
proposed encroachment of the garage and the nonconforming creek setback of the existing
detached accessory structure.
• Section 14.16.130, Exclusions to the required minimum yards, allows for architectural features,
such as fire places, to encroach no more than 2' into any required yard setback. The project
proposes the fireplace to encroach 1' into the front setback.
Chapter 18 — Parking Standards
The project is required to provide 2 -covered off-street parking spaces with a 10' driveway width and
provide a minimum interior dimension of 20'x20'. The project complies with these standards.
Chapter 25 — Environmental and Desiqn Review Permit
The project is subject to design review as it's a new single family on a flag/panhandle lot and the upper
story is over 500 sq. ft.
Review Criteria
➢ Materials and Colors
o The design criteria recommends that colors be earthtone/woodtone and for the use
of natural materials. The project currently proposes Roseburg Breckenridge wood
veneer siding painted "Farrow and Ball All White #2005" with wood comer trims.
➢ Upper -Stories
o The design criteria for upper -story window placement, for new construction, is
intended to minimize significant privacy concerns, by assessing that the design does
not look directly into private backyards and adjacent living space. The applicant
submitted a narrative (Exhibit 3) justifying their upper -story window placement. In
4
summary, the window placements are 30+ feet away from the adjacent property lines
and either have an existing mature landscaping obscuring the line of site or are
proposing to plant new landscaping to minimize the impact.
o Neighborhood Compatibility requires new development to be a compatible design
where there's a prevailing design on both sides of the streets for the length of the
block. The project is in a somewhat eclectic neighborhood with no single dominant
architectural style. The neighborhood has a variety of styles, including Ranches,
Spanish style, Mediterranean, and Victorians. Most of the homes on that block are
two stories and are large homes. The proposed project is about average in size
compared to the homes located on the same block, see Exhibit 4 for an analysis of
neighboring homes in the same block.
➢ Landscape Design
o The project proposes to maintain the existing mature trees along the north property
line and to preserve the tree lined driveway. Should the revised creek setback be
accepted the City would condition the area within the creek setback to be
landscaped with native vegetation, as recommended in Biological Assessment.
➢ Drainage
o The drainage plan includes the use of three (3) bioretention areas and two (2)
swales. The plan has been reviewed and approved by DPW. However, due to the
public concern regarding adequacy of the drainage improvements staff has
requested the applicant to complete the Storm Water Control Plan now, during the
Planning phase as opposed to deferring it to the Building Permit Phase. When the
report is completed and submitted to Planning it will be rereferred to DPW for review.
NEIGHBORHOOD CORRESPONDENCE
Notice was sent to property owners and occupants within 300 feet of the site within 15 days of the
board meeting. Notice was also posted on the site a minimum of 15 days prior to the meeting.
At the time staff's report was prepared and distributed staff received one (1) comment due to the
noticing for this hearing. The comment was regarding preserving the mature trees along the north side
of the property. Staff has informed the concerned party that, should the project be approved, those
trees would be included as part of a required landscape plan, as they were taken into consideration for
the upper story window privacy, and should they be removed in the future they would be required to be
replaced.
CONCLUSION
Staff has found the project to be substantially consistent with General Pan and Zoning Ordinance, but
staff is seeking the Boards input regarding the design elements and the creek encroachment.
EXHIBITS
1. Vicinity Map
2. Biological Assessment, Creek -Riparian Zone Setback Report, Dated November 14, 2018
3. Upper Story Window Placement Justification, from Property Owner, Received September 18, 2018
4. Neighborhood Site and Development Survey, Compiled by staff on March 11, 2019
5. Geotechnical Evaluation, Dated March 10, 2018
6. Geotechnical Supplement, Dated March 5, 2019
7. Reduced Plans
Full-sized plans have been provided to the DRB members only
cc: Bob Porter, 1723 Grand Ave. San Rafael, CA 94901
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ENVIRONMENTAL CONSULTANTS
November 14, 2018
Mr. Robert Porter
1723 Grand Avenue
San Rafael, CA 94901
RE: 1446 Grand Avenue (APN: 015-201-39), San Rafael, CA
Biological Assessment, Creek -Riparian Zone Setback
Dear Mr. Porter:
At your request, WRA, Inc. (WRA) conducted a biological assessment for proposed residence
construction focusing on potential creek and riparian zone effects that the project could cause at
1446 Grand Avenue (Study Area), in the City of San Rafael, Marin County, California (Figure 1).
A site visit was made by WRA on November 12, 2018 to observe existing conditions.
Existing Conditions
The Study Area was the mostly? vacant lot where construction of a single family residence is
proposed. The lot is located in a long established residential neighborhood northeast of the
downtown business district of San Rafael, CA. The elevation of the Project site is approximately
65 feet above mean sea level and is on relatively level ground. The main project area is
accessed from Grand Avenue by an entry lane between existing residences that was lined on
both sides by planted flowering plum trees (Prunus cerasifera). The parcel was observed to be
mostly vacant and had been maintained by removal of most vegetation (Photograph 1). A
cottage and small shed occupied the back northeastern corner of the lot (Photograph 2). The
soil type is mapped as Xerorthents-Urban land complex (NRCS 2018), 0 to 9 percent slopes
which is generally described as fills and. reworked soils associated with developed areas.
The area experiences mild winters with precipitation falling as.rain during the winter months
between October and May, and summers are warm and dry. A segment of Sister's Creek runs
from east to west along the eastern boundary at the back of the lot. The creek had minimal flow
at the time of the site visit with occasional pools, and it likely can be classified as an intermittent
stream (flows'regularly during the winter wet season).
Vegetation that was observable during the site visit included non-native forbs, such as Bermuda
buttercup (Oxalis pes-caprae), English ivy (Hedera helix), and ox tongue (Picris echioides),
shrubs, such as Himalayan blackberry (Rebus armeniacus) and French broom (Genista
monspessulana), and trees, including green wattle (Acacia decurrens), golden wattle (Acacia
longifolia), and native coast redwood (Sequoia sempervirens). Both species of Acacia trees (2
to 6 -inch diameter DBH), which tend to be undesirable invasive non-native trees were growing
along the creek banks (Photograph 3) and around a stockpile of bricks at the southern
boundary, and the native coast redwood trees (25 to 36 -inch DBH) were along the northern
fence (Photograph 4).
2169-G East Francisco Blvd., San Rafael, CA 94901 (415) 454-8868 tel (415) 454-0129 fax info@wro-co.com www.wra-co.com
property (Figure 3). There were four special -status plants with known occurrences in the
general vicinity that were initially considered (before site visit) to have potential to be present
because of proximity to the Project, and they are listed below. None of the four plant species
were determined to be present within the Project site since the type of soil and habitat that the
plants normally require, which are serpentine soils and grassland habitat were not present.
Because the Project site is well maintained by keeping it cleared of weeds and other vegetation
and trimmed trees and lacks serpentine soil, three of the plants were determined unlikely to be
present. A fourth plant requires tidal marsh habitat, and was determined to be not present.
Therefore, no impacts to special -status plant species will occur as a result of the proposed
project and no further actions concerning these plants is necessary.
Common Name
Species
Special -status
Presence/Absence
Rank
Napa false indigo
Amorpha californica var. napensis
CNPS 113.1
Not Present. Has an
affinity for serpentine soil
which is not present on
the project site and plant
was not observed during
site the visit.
Tiburon buckwheat
Eriogonum luteolum var. caninum
CNPS 113.2
Not Present. Has an
affinity for serpentine soil
which is not present on
the project site and plant
was not observed during
site visit/bloom period.
Point Reyes salty bird's-
Chloropyron maritimum ssp.
CNPS 113.2
Not Present. Restricted to
beak
palustre
tidal marshes.
Marin western flax
Hesperolinon congestum
'CNP&fl3.1
NotPresent. Hasan -
affinity,for serpentine soil.
which is not present on
the project site and plant
was not observed during
site visit.
The CNDDB and IPaC data bases indicate that few wildlife species occurrences are known in
the general area. The wildlife that are nearest in proximity to the Project site are animals that
require special habitats for their existence, such as Ridgway's clapper rail (Rallus longirostris
obsoletus) in tidal marshes, California least tern (Sterna antillarum) on sandy beaches/dunes,
and marbled murrelet (Brachyramphus marmoratus), a sea bird. The special habitats these
species require are not present. One wildlife species that has some potential to use the creek
habitat for migratory purposes only, because the channelized nature is not conducive as
sustainable habitat, is the California red -legged frog (Rana draytonii). However, the nearest
known occurrence of this frog is more than three miles to the east with difficult terrain and
development areas in between, and it is not likely to be present. Finally, pallid bat (Antrozous
pallidus) has occurrence in the area but is not likely to be present because of the continuous
presence of human activity in the neighborhood and the cottage and shed on the parcel are
regularly used and maintained. Pallid bats are sensitive to human encroachment and activities.
There is some potential for nesting birds to be adversely impacted during construction or if trees
will be removed. The Migratory Bird Treaty Act is a law that protects most bird species,
particularly during the breeding/nesting season. It is illegal for projects (construction) to cause
death of birds either through direct mortality or by destruction or failure of nests/eggs. Migratory
birds could potentially nest in the trees in the project area during the bird breeding season,
to activities and will not be harmed or will abandon nests. No adverse effects will result
to nesting birds if these recommendations are implemented.
• Outdoor lighting should not be directed directly toward or into the creek channel area.
Outdoor lighting should be directed downward and diffused as much as possible.
This concludes this biological assessment of 1446 Grand Avenue, San Rafael, CA. If additional
information is required or there are questions, please contact Douglas Spicher at 415-524-7536
or by email at spicher@wra-ca.com.
Sincerely,
Douglas Spicher
Principal
References:
California Department of Fish and Wildlife (CDFW). 2018. California Natural Diversity -
Database. Wildlife and Habitat Data Analysis Branch, Sacramento, CA.. Accessed
November 2018.
San Rafael Muni.cipal.Code. 2018. Chapter 14.16 Site Use and Regulations; Section 14.16.080.
City. of.San Rafael, CA.
Design Consultants Group. 2018. Site plans for 1446 Grand Avenue. Design Consultants
Group, 3900 Geary Blvd., Suite 201, San Francisco, CA 94118.
U. S. Fish and Wildlife Service (USFWS). 2018. Information for Planning and Consultation
(IPaC) Species Lists, Sacramento Fish and Wildlife Office. Available online at:
http:/Iwww.fws.gov/sacramento; Accessed November 2018.
NRCS. 2018. Soil survey Marin County. Accessed online at Novembe 2018 at:
https://websoilsurvey.sc.egov.usda.gov/AppA/\IebSoilSurvey.aspx
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Photograph 1. The lot at 1446 Grand Avenue in San Rafael, CA looking southwest. The lot is kept
well maintained by clearing non-native vegetation.
Photograph 2. A cottage and shed exist in the northeastern corner of the lot and is set adjacent to
Sister's Creek which flows at the right side of the photograph.
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ENVIRONMENTAL CONSULTANTS
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Photograph 5. Sister's Creek flows into a box culvert at the soutnwestern corner oT the property. ne
wingwall and outside curve of the creek make conditions for a stable creek bank.
Photograph 6. The garage of the proposed new residence will encroach into the setback from top of
bank of Sister's Creek, and will be approximately 10 feet back from top of bank. No vegetation will be
impacted by the position of the garage corner near the creek.
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ENVIRONMENTAL CONSULTANTS
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Photograph 5. Sister's Creek flows into a box culvert at the soutnwestern corner oT the property. ne
wingwall and outside curve of the creek make conditions for a stable creek bank.
Photograph 6. The garage of the proposed new residence will encroach into the setback from top of
bank of Sister's Creek, and will be approximately 10 feet back from top of bank. No vegetation will be
impacted by the position of the garage corner near the creek.
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ENVIRONMENTAL CONSULTANTS
City of San Rafael page 1 of 2
Planning Department
Alan Montes ,Assistant Planner
RE: (ED13-040) New Single Family Residence
Vacant Lot On Grand Ave; APN: 015-210-39
Second story window placement and privacy impact on adjacent properties for a
New single family residence.
North adjacent property:
There are three second story windows facing the north. Two windows are
Bedroom Egress and the third is a master bathroom window.
These windows will have minimum impact to the adjacent property because the
location of the windows are set back over 31 feet from the property line. There
are three mature redwood trees along the north property line that are 50+ feet tall
and offer a green barrier the length of the purposed new single family home.
East adjacent property:
There are six second story windows facing the east. Two in the master
bedroom . two for the master closet and two for the master bath.
These windows will have minimum impact to the adjacent property because the
location of these windows are over 40 feet from the property line. Where is
existing trees and vegetation that forms a green barrier along the east property
line. New trees that meet fire department requirements will be planted in this
area to increase the green barrier.
South adjacent property:
There is five second story windows facing south. Three master bedroom
windows.
Two windows are in spare bedroom. These windows will have a minimum impact
to the adjacent property because the windows in the spare bedroom are over 32
feet from the property line and the master bedrooms windows are 42 feet from
the property line. There is an existing big leaf maple tree and a dense green
716MIMME
barrier of bay tree saplings along this property line. New trees are purposed to
be placed and maintained in the 10 foot setback that meet fire department
requirements to increase the green barrier.
West adjacent property:
There is five second story windows facing west. Two in bedroom #1. Two in
bedroom #2 , and One in the hall bathroom this window will with have obscure
glass. These windows will have minimum impact to the adjacent property
because the windows are 30 feet from the property line.
Overall there is an existing green barrier surrounding the property and with the
addition of some new SRF® approved trees and the second story set back of at
least 30 feet in all directions and up to 50 feet in some areas Impact on adjacent
properties should be minimal.
UOTGUMIUM
Exhibit 4
Site
Lot Size
Living sq. ft. +
Garage
2 story?
Structure to Lot
Size
1446 Grand
(Most Restrictive Calculation)
All Structures and Only Flag
Portion of Lot*
12,512
4,475 (Gross)
YES
0.36
1446 Grand
(Most Lenient Calculation)
Only SFD and Full Lot Size
14,227
4,049 (Gross)
YES
0.28
Averaged from List Below
Minus Subject Site
11,375
3,676 (Net)
0.32
2 Acacia
5,700
2,400
NO
0.42
4 Acacia
5,200
3,210
YES
0.62
23 Olive
15,100
3,581
YES
0.24
21 Olive
6,372
1,823
YES
0.29
19 Olive
6,864
3,973
YES
0.58
49 Palm
7,640
3,922
YES
0.51
45 Palm
8,586
4,300
YES
0.50
43 Palm
17,712
3,272
YES
0.18
37 Palm
9,350
4,560
YES
0.49
31 Palm
16,290
4,289
YES
0.26
25 Palm
10,505
3,230
YES
0.31
19 Palm
11,484
3,936
YES
0.34
15 Palm
10,192
3,594
YES
0.35
11 Palm
10,788
3,702
YES
0.34
7 Palm
13,400
3,322
YES
0.25
1404 Grand
23,560
7,606
YES
0.32
1412 Grand
13,425
3,182
NO
0.24
1420 Grand
14,440
4,599
NO
0.32
1430 Grand
5,148
3,058
YES
0.59
1434 Grand**
14,860
5,244
YES
0.35
1436 Grand
5,400
1,142
NO
0.21
1440 Grand
20,790
3,759
YES
0.18
1450 Grand
10,000
4,220
YES
0.42
1456 Grand
13,515
4,584
YES
0.34
1460 Grand
14,893
2,346
YES
0.16
1464 Grand
4,536
2,718
NO
0.60
*This information is pulled from the County Assessor's records. It's unclear if the accessor includes detached
accessory structure as part of the Building Living Area sq. ft. used to create this table.
**flag lot counted total lot size.
7
rlx 07 NGINEL-.1�[G, INC. File P-_ . j-rp
GEOTECHNICAL EVALUATION
PROPOSED DWELLING
1446 GRAND AVENUE
SAN RAFAEL, GA
.�_T�[�'+ • »-rte ��1 f�.�-
RECEIVED
M_:. MAY 2 9 2018
PLANNING
I
GEGEN INEERI.NG, INC.
Geotechnical Engineering Consultants Robert H. Settgast P.E. G.E.
124 Paul Drive, Suite #10.5 Phone (41 S) 492-1747
San Rafael, CA 94903 rhsettgast@a hotmail. com
Robert Porter
1753 Grand Ave
San Rafael, CA 94901
GEOTECHNICAL EVALUATION
PROPOSED DWELLING
1446 GRAND AVE
SAN RAFAEL, CALIFORNIA
1. INTR OD UCTION & BACKGROUND
March 10, 2018
File 1-183-rpl
Our firm has been retained by the addressee to perform the entitled services. The designers are
Design Consultants Group of San_ Francisco. Our terms are outlined in a 2/19/18 agreement ,and
in the final section of this report.
The information & recommendations contained herein are based on 2/28 & 3/3/18 site
investigations that included: reconnaissances of the site and its environs, three manually
excavated — 4 ft deep test pits that were extended to —6 .ft depths with a manual auger, and
multiple soundings with an impact probe -for strata correlation & subsoil - evaluation.. -- .---- _-
Although basements or retaining walls are not currently planned, we include criteria for their
design in case if they are included.
Z SITE & PROJECT DESCRIPTION
As the attached Site Plan & photos show, this trapezoidal northwesterly facing"flag lot" is set
back —120 ft from Grand Ave. It is —100 ft wide and extends rearward 85 to 100 ft on to the
channel of a seasonal stream. Its westerly front segment is accessed from Grand Ave through an
unpaved driveway inside its southwesterly boundary. The adjacent parcels are occupied.
The south house corner will encroach to within —25 ft from the stream bank which falls —10 ft
over M 40 ft to the flow -line. The site surfaces are irregular with localized variations of l or 2 ft.
It generally slopes southerly at irregular grades averaging I % or 2 %..
This dwelling will have a partial second story and raised wood floors. Its attached garage will
have an on -grade slab. No special foundation requirements are anticipated.
3. GEOLOGY c& SUBSOILS
This site is mantled by up to 1-1/2 ft of fill, comprised of stiff sandy clays that rendered hard
resistance to our impact probe.
Alluvial deposits comprised mainly of stiff sandy clay with random rock fragments underly the fill
and extend 4 to 6 ft deep.
File 1-183-rp -pg 2 - GEOENC _,sRING INC
Very stiff to hard sandy clays & clayey sands with rock fragments underlie the sandy clays --and
extend below depths which affect this project. We have classed them as *residual soils.
"'Residual soils are bedrock that has been weathered in place to consistencies of very stiff or hard
soils but still show, favorable_ foundation properties.
We noted random potential for possib–l-e—ink-swell with respective decreasix�g az�d increasing
moisture contents in the tipper soils, which is common for such settings.
Wetness but no groundwater was noted in our test pits and borings. Our exploration followed
some light rainfall during the rainy season. We expect that perched groundwater may rise to within
2 or 3 ft from grades during heavy rainfall.
4. DISCUSSIONS & CONCLUSIONS
4.1 SUMMARY, ,S'EISM1C CRITERIA, & FOLLOW UP SERVICES
Subsoil conditions here have favorable foundation properties. The 25 ft proximity of the house to
the top of the creek banks poses no special. concerns. Nonetheless, our recoMmendations include
provisions for the foundations to span uneven support from any possible bank recession, or
unanticipated subsoil irregularities.
If our criteria poses significant cost penalties, we should be notified --in such cases we would
review our data develop less costly criteria if possible. Foundation plans must be approved by the
geotechnical engineer, and shall be complete without requiring contractors to refer to this report.
Foundation excavations and related earthwork shall must be monitored and approved by the
geotechnical enginee-- and our acceptance is subject to this.
Site Class "D "( stiff soils) applies for seismic design at this site.
4.2 FOUNDATION DESIGN CIZITF,IZIA
1. Foundations shall be interconnected and shall penetrate at least 1-1/2 ft below adjacent
exterior grades. They must also penetrate as deep as the lowest grades within 0' ft. Isolated
members may be acceptable pendng our approval.
2. Foundations shall be capable of spanning 8 ft (assuming fixed end conditions). Alternatively
two horizontal #5 bars both tbp & bottom will suffice for this.
3. Such foundations may be sized for allowable soil pressures of 2,000 psf for dead and
sustained live loads; but should be limited to 1,500 psf for sustained dead loads. They may
be increased to 2,800 psf to include wind & seismic forces. Weight of concrete below
grade may be discounted. These pressures should be reduced byl/3 for isolated members.
4. Lateral seismic loading may be resisted using allowable friction factors of 1/3 and allowable
equivalent fluid passive earth pressures of 300 pef.
The standard 1.5 code safety factor should be applied for sustained lateral loads.
4.3 FOUNDATION DRAINAGE & PROTECTION
1. Exterior grades shall slope away from the dwelling. The slope onfigurations will depend on
the genaral site grading, but we expect that a 2 inch fall over 5 ft would suffice .
File 1-183-rp -pg 3 -- GE®ENC _._RING INC
2. Exterior foundation members should extend above grade for protection to the framing.
actual freeboard heights will depend on localized topography and grading, but we expect
freeboard heights 1/2 ft would suffice here .
3. Upslope exterior foundation members and interior members that act as
- -_ - _ - -retain walis_should be pro_v_ded with-backdrains______.__-- --_-------------- --- _.... .___.._-
penetrating 1 ft below interior or subfloor grades, or as required by the geotechnical
engineer. They may consist of bottom -perforated pipe in drainrock, installed as specified for _
retaining wall baekdrains in Sect 4.5.
4. Subfloor grades must slope downhill for drainage, and should be no lower than the adjacent
exterior grades unless there are no other options. The lower intersection of the foundation
members should be provided with 1 inch weepholes, placed just above grade.
5. Subfloor grades should be covered with moisture barriers or concrete (rat proofing) to
mitigate Subfloor humidity from ground moisture. This is in addition to a complete venting
system. Rat proofing (concrete cover) shall be applied to subfloor grades that lie below
exterior grades, unless 3 % slopes and direct unobstructcd ventilation can be achieved.
4.4 RETAINING /BASEMENT WALLS (IF APPLICABLE)
I . Retaining wall foundations may follow the criteria outlined in the preceding section.
2. Retaining/basement walls may be designed for allowable equivalent fluid active earth
pressures as follows: of 55 pef. These pressures include seismic loading. They may be
reduced to 45 pcf for detached site walls
3. Uniform lateral pressures equal to one third of any anticipated surcharge pressures, but at
least 75 psf for walls supporting streets, driveways, or garage slabs should be added to the
equivalent fluid pressure.
4. Where backslope grades above the wall rise, the efp for the upper 3 ft should be increased
in proportion to 2/3 the upslope rise; ie an upslope rise of 40% (2.5h:Iv) corresponds to a
pressure increase of 27 %. The efp may be reduced by 15% for detached site walls that
support no pavement or structure. In no case need the efp exceed 75 pcf.
5. The active pressures influence from any upslope detached terraced retaining walls may
follow our criteria for rising backslopes-- by assuming an imaginary backslope rising
from the top of the lower wall and meeting the upper wall at 2/3 its height.
Segmented retaining walls such as Versa -Lok may be designed to the manufacturers
criteria—when approved by the geotechnical engineer..
4.5 BACKFILL & BACKDRAINAGE
Backfill behind retaining walls, which support or are integrated with other structures, must
always be placed, moisturized and compacted, before framing or subsequent construction.
This is to minimize post construction deflections.
Retaining walls shall be backdrained and provided with separate surface drainage to avoid
infiltration and related backdrain overcharging. When acting as building walls, they must
also be waterproofed. Backdrains may consist of bottom -perforated pipe in drainrock
blankets at least 6 inches wide. These pipes should be placed just above the bottom of the
drainrock. They may discharge at most locations where prolonged seepage is acceptable.
File 1-1 S3-rp -pg 4 - GEOENG ,—RING INC
If Class 2 Permeable drainrock (or equivalent) is not used, drainrock should be separated
from the adjacent soil with geotextile filter cloth. Drainrock should extend from the wall
bottom upward to within 1-1/2 to 3 feet from the top depending on the wall height. The
upper backfill should be a clayey soil with a low permeability to prevent migration of surface
water into the backdrain.
Weepholes may be used in lieu of (or with) perforated pipe, where wall seepage is accept-
able. They are more reliable but still require drainrock. They should be about 1 inch in
diameter, and spaced at about 4 feet intervals along the base of the wall.
The height of the drainrock conduit may be reduced to 1 foot if structured backdrain material
(such as Miradrain) is used behind upper section of walls. It should penetrate to the bottom
of the drainrock for hydraulic conductivity.
4.6 SITE PREPARATION, GRADING, & DRAINAGE
Gro- nd surfaces should be sloped for rapid drainage away from building areas.
Roof drainage should be channeled downslope away from the structures.
Discharge into dry wells (gravel tilled unlined excavations) should be avoided near the
stream banks. Typical "T" dispersal flumes, comprised of 4 inch top -perforated pipe
embedded —1/2 ft with course gravel (or comparable rocks) would suffice for erosion
protection --a drawing is available on request. Surface water should never be introduced into
backdrains or other subterranean drainage systems that utilize perforated pipe or drainrock.
Such systems are intended only for groundwater.
4.7 EXCAVATION ANIS .ENGINEERED PILL PLACEAlfENT
Areas to receive fill must be cleared and stripped of topsoil. Stripping depths should be
determined during carthwork but we expect they will range up to 1/2 foot
Exposed should be scarified c&. moisture conditioned to near optimum, and compacted to 90%
of the maximum dry density as determined by the Modified AASHTO test.
Engineered fill (that placed below buildings and pavements) should be approved by the
geotechnical engineer. It should be low or medium plasticity, and be free of organic and
debris. The on. -site soils and bedrock, will suffice as engineered fill after top soil removal.
Engineered fill should be spread in approximate 3 inch lifts, and moisturized and compacted
as outlined above -for the subgrades.
OSHA requirements must to fbllowecl. In No Case May Workman Enter the space between
untraced cuts over S fi high, and retaining walls or their f om work.
4.8 SLABS AND PA VEMENTS
Subgrades below slabs and pavements should be prepared as recommended above, and
approved by the geotechnical engineer. Prior to baserock or concrete placement, subgrades
for interior slabs shall be sloped for drainage, compacted as recommended above, and rolled
to smooth surfaces. At least 4 inches of free draining bascroek should be placed and
compacted over the subgrade to act as capillary breaks, and to provide subslab drainage for
potential groundwater at the lower corners of the baserock blanket. Drain outlets through the
low foundation intersections should be provided.
File 1-183-rp - pg S -- GEOE _ .EERING INC
Durable impervious barriers„ should be placed below the slab to impede moisture permeation
unless slab dampness is acceptable. Current practices recommend against sand over the
membrane due to its tendency to displace during concrete
placement resulting in variable slab thiclozesses.
Floor slabs within living areas that abut retainingwlils will_require__e_xtra.precautions_wit h
respect to drainage and waterproofing. In view of the potential seepage problems inherit with
such slabs, we suggest that they be provided with pressure treated "sleepers".
5. CLOSURE AND LIMITATIONS
By accepting this report the client and other recipients acknowledge their understanding and
acceptance of the following terms and conditions. They also acknowledge that no verbal or written
guarantees were made by the undersigned.
Even though we see no reason to suspect that the soil or foundation behavior will differ from our
predictions, one must recognize that factors contributing to hillside and foundation instability,
seepage, and other geotechnical related problems cannot always be detected.
Our work is limited to geotechnical aspects of design. We may cite minimum criteria, but structural
design and inspection are the responsibility of the structural engineer and/or designer. Even though
we may comment on toxic materials, their identification is excluded from our services and
responsibility. Hydrological and flood studies are also excluded from our work scope. Identification
of underground lines is the contractor's responsibility.
Earth slippage and su.bfloor water are sometimes -.unavoidable especially during rainfall and/or
irrigation. Subdrain performance can never be predicted and blockages in such system are common.
Cracks in wallboard and tile, as well as some distortions in hardwood floors develop in most
structures from normal wood shrinkage and relaxations. Concrete curing and stress cracks will also
develop. These occurrences cannot be avoided and we are not responsible for their effects. Since we
are not contracted to provide firll time observations, we cannot be held liable for construction errors.
This report represents our best judgment based on the available information and complies with
current standards of practice for comparable projects. No forms of warranty or insurance coverage
are expressed or implied in our reports or other communications.
It is also understood that certain risks must be assumed for all types of foundation and earth systems.
These risks can always be lessened by upgrading these systems even though the margin of additional
safety may be small compared to the additional costs involved. Although the engineer may assist in
selection of the optimum balance between safety and economy, the client and all recipients
understand that the risk is their own.
If a wrongful claim is made against GeoEngineering, Inc. for any act relating to our professional
services, its, initiator(s) shall pay for all costs and lost time associated with our defense.. In any case,
our liability cannot exceed our fee for this project. We cavy no errors and omission insurance
-000
We trust that this report provides the information required. You may contact us for clarification.
RHS: rhs
Attachments: Photos on cover & Site Plan
Respectfully submitted,
GE, OENGINEERING, INC.
Robert TL Settgast
Prgfessional Geotechnical Engineer
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PROP05ED 1) WRLIN6
1446 C—RAND A VE
SAN RA FA EZ, CA
Exhibit GEOENGINEERING, INC.
Geotechnical Engineering Consultants
124 Paul Drive, Suite #105
San Rafael, CA 94903
Robert Porter
1753 Grand Ave
San Rafael, CA 94901
Phone & Fax (41 S) 492-1747
Robert H. Settgast P.E. G.E.
rhsettgast@hotmail. cont
GEOTECHNICAL SUPPLEMENT
GARAGE REPOSITIONING,
SETTLEMENT BEHA VIOR,
STREAM BANK STABILITY, AND
BIO RETENTION PLAN
PROPOSED DWELLING
1446 GRAND AVENUE
SAN RAFAEL, CA
March 5 ,2019
File 1-183-rp
Our firm had submitted 2/10/18 geotechnical evaluation report to the addressee. The same terms
and liability limitations outlined in that report still apply. We are now responding to issues raised
by the neighbors or municipality. On 2/25 and 2/28 we observed the site conditions and
performed a single supplemental auger boring for correlation with existing data.
The planned dwelling and attached garage initially encroached to the stream setback, which is
25 ft from the top of the stream banks. The attached garage was subsequently shifted — 12 ft
southerly which now places its southerly. corner — 12 ft from the stream banks. (attached Site Plan.
Our supplemental boring at the southerly corner of the revised garage position encountered stiff
sandy clays comparable to those identified in our earlier borings throughout the site. ,
The foundation criteria in Sect 4.2 still applies— but as a precaution, we have recommended that the
perimeter foundation members within 7 ft from the southerly garage corner (which are nearest the
setback) be designed to cantilever for 7 ft. Three #5 bars at the top of the foundation steel. cages
would suffice for this.
The steam banks show no signs of instability nor unusual sloughage--even despite the near record
rainfall three days earlier. Two bio -retention structures will lie within — 12 ft from the stream
banks. Another will lie in fromt of the new dwelling. From a review of their design, and
discussions with the engineer who designed them, we believe that they will have little or no effects
on stream bank stabilities. Nonetheless, their installation shall be monitored and approved by the
geotechnical engineer.
Foundation settlements will be typical for such structures in comparable settings, and will be within
acceptable limits. Recognizing the variables involved with settlement predictions, we expect that
there will be some minor cyclic rising and settling of the foundations from respective increasing
and decreasing soil moisture contents. Long term settlements of 1 or 2 inches over 30 years, with
one half being differential, are estimated.
File 1-183-rp -pg 2 - GEOENGINEERING INC
Site settlements are not expect to significantly affect the gravity flow for typical drainage and
sewer systems.
We have reviewed the plans for the bio retention plans (Sheet C-1.0 & Cl .5) and the storm water
drainage plan (Sheet C -3) --all are revised on 12/5/18. We have also discussed them with the
engineer who had prepared them, and find them acceptable.
- 000-I
In view of the above points, we find the items addressed in the title and in the preceding
paragraph, to meet the intent of our criteria, as well as other normal standards for similar
projects in comparable settings.
We trust that this report provides you with the information currently required.
You may contact us for clarification.
RHS: rhs
Site Plan & Photos Attached.
Respectfully submitted,
GEOENGINEERING, INC.
Robert H. Settgast
Professional Geotechnical Engineer
No. GMW764' );�I
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