Item 4C - 061323-ADUs-BOZA 1
BOARD OF ZONING ADJUSTMENT MEMORANDUM
TO: Board of Zoning Adjustment
FROM: Brad Mueller, Director of Planning & Development Services
Charles Ferro, Senior Planning Manager
Karl Guiler, Senior Policy Advisor
Lisa Houde, Senior City Planner
DATE: June 13, 2023
SUBJECT: Accessory Dwelling Unit Adopted Ordinance Overview
EXECUTIVE SUMMARY
On May 4, City Council adopted Ordinance 8571, which updates the regulations for
accessory dwelling units or ADUs. The purpose of this item to update the Board of
Zoning Adjustment on the adopted ordinance.
City Council identified updating the ADU regulations to increase their allowance in the
community as one of their top work program priorities for 2022-2023. The ordinance was
limited to changing regulations related to the ADU saturation limit, size limits, as well as
code simplification and clarification. In addition, the ordinance changes will facilitate
process improvements to further simplify the administration of ADU applications. The
ordinance will go into effect on September 1, 2023.
BACKGROUND
Staff met with BOZA on February 14 to provide an overview of the current ADU
approval process and discuss the potential code changes. The Board of Zoning
Adjustment was supportive of removing the saturation limit, increasing the size limits,
and all of the code clarification and process improvements. The discussion focused
primarily on the changes to size limits as BOZA reviews floor area variances for ADUs.
Overall, BOZA noted no major concerns and considered the changes to have limited
impact to BOZA.
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SUMMARY OF ORDINANCE 8571
The adopted ordinance focused on four main focus areas listed below. Attachment A
includes more detail on each of the changes, and the full ordinance language can be found
in Attachment B.
• Eliminating saturation limit
• Considering changes to size limits
• Clarifying and simplifying the code
• Extend approval expiration period
• Flexibility for height of existing structures
• Lockable separation of attached ADUs
• Limited accessory units
• Owner occupancy – LLCs and temporary rental exemptions
• Public notice requirement
• Improving the process
• One-step review
• Addressing
• Declarations of use
• Self-service handouts/videos
SIZE LIMITS
As BOZA reviews all floor area variances for ADUs, the background and analysis related
to the size limit changes is included below.
Background
The City Council’s objective for the ADU regulation update work program priority was
to increase the allowance of ADUs in the community. In the 2022 evaluation of the most
recent changes, it was concluded that increasing the allowed size of detached ADUs from
450 square feet to 550 square feet had a significant impact on the ADUs created since the
most recent code updates. No change was made to the allowable size of attached ADUs
in the previous update.
Comparable Cities
There is significant variability among comparable cities that limit the size of ADUs.
Generally, a typical maximum size is about 800 square feet. Maximum sizes tend to be
smaller in Colorado cities, however, although still range between about 500 and 1,000
square feet.
Evaluation Results
Over three-quarters of the detached ADUs that were constructed since 2019 would not
have previously been permitted due to maximum floor area. Modifying the allowed
square footage by only 100 square feet made arguably the most significant change in the
number of ADUs allowed. These ADUs were still subject to all of the typical zoning
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requirements that ensure compatible residential development, such as solar access,
interior side wall articulation, bulk plane, and building coverage requirements. Many of
these standards vary based on the lot size as well, which also impacts how large of an
ADU a particular lot can accommodate.
In addition, while completing the evaluation, the measurement of ADU floor area was
one of the most frequently cited issues and least clear parts of the current code language.
Removing the unique method of measuring floor area for ADUs from the code would
significantly reduce review time and increase clarity for both applicants and city staff.
Analysis
Further increasing the allowed floor area of ADUs could allow for more ADUs to be
constructed in Boulder as there may be greater demand for slightly larger ADUs and
potentially greater return on investment for property owners. As noted in some of the
public input received, an increased size could also allow for additional types of
households, such as small families, to find ADUs a feasible housing choice.
The original intent of the size limit for attached ADUs was to ensure that the accessory
dwelling unit is smaller in size and therefore subordinate to the main home. The current
requirement of 1/3 of the principal structure presents challenges for people with homes
smaller than 3,000 square feet. The size restriction in some cases leads to impractical and
costly remodeling work such as walling off portions of a basement to meet the size limit.
A limit of 1/2 or 1,000 square feet (whichever is less) would still ensure that the ADU
remains smaller than the principal structure, but would provide more flexibility for
adaptive reuse of smaller homes. Homes up to 2,000 square feet could have an ADU up
to half the size of the principal structure, and those larger than 2,000 square feet would be
limited to a 1,000 square foot attached ADU.
Correspondingly, to preserve the existing incentive for owners to pursue affordable units,
the maximum size of affordable ADUs would also need to be increased (up to 1,000
square feet for detached, and two-thirds or 1,200 square feet for attached). In the 2022
survey of ADU owners, about one-quarter of owners who pursued an affordable ADU
stated that they did so due to the incentive allowing a larger ADU.
Past Public Input
The initial staff recommendation during the 2018 ADU update was to increase the
permitted size of detached ADUs from 450 square feet to 800 square feet. Ultimately, the
maximum size of detached ADUs was increased to 550 square feet. For attached ADUs,
the original staff proposal in 2018 was to increase the size limit from 1/3 of the principal
structure or 1,000 square feet to ½ of the principal structure or 1,000 square feet. This
change was not ultimately adopted, and the limit remains 1/3 of the principal structure or
1,000 square feet for attached ADUs. However, in a questionnaire of nearly 200 residents
at the time of the 2018 update, a majority of respondents (62%) supported the change,
and about one-quarter of those respondents indicated they would support increasing the
limit even further.
To help visualize the size differences, staff compiled photos of a variety of the ADUs that
have been approved and constructed since 2019 in Attachment C. These photos include
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several ADUs that were approved around 800 square feet for detached ADUs and
between 1,000 and 1,200 for attached ADUs, by either utilizing the increased size limit
incentive for affordable ADUs or by receiving a variance approval from the Board of
Zoning Adjustment.
Ordinance 8571 modifies the maximum size of ADUs as shown in the following table:
ADU Type Current Size Limit Proposed Size Limit
Attached 1/3 of principal unit or 1,000
square feet, whichever is less
1/2 of principal unit or 1,000
square feet, whichever is less
Detached 550 square feet 800 square feet
Affordable
Attached
1/2 of principal unit or 1,000
square feet, whichever is less
2/3 of principal unit or 1,200
square feet, whichever is less
Affordable
Detached 800 square feet 1,000 square feet
Historic
Attached
1/2 of principal unit or 1,000
square feet, whichever is less
2/3 of principal unit or 1,200
square feet, whichever is less
Historic
Detached 1,000 square feet 1,000 square feet
NEXT STEPS
Staff is currently working on the associated process improvements to streamline ADU
applications and implement the ordinance changes in preparation for the effective date of
September 1.
ATTACHMENTS
Attachment A: Ordinance 8571 Summary
Attachment B: Adopted Ordinance 8571
Attachment C: Photos of Recent ADUs in Boulder
Ordinance 8571 Summary
ACCESSORY DWELLING UNIT REGULATIONS
Background
The City Council identified updating the accessory dwelling unit (ADU) regulations as one of their top work program
priorities for 2022-2023. The objective of the project is to increase the allowance of ADUs in the community. The scope of the
project includes:
•Eliminating the saturation limit in the RL-1 and RL-2 zoning districts
•Considering changes to the ADU size limits
•Clarifying and simplifying the code
•Improving the approval process
Saturation Limit
Remove the current restriction that limits ADUs in the RL-
1 and RL-2 zoning districts to only 20% of properties
within a 300 foot radius.
Clarification & Simplification
Staff completed an evaluation of the most recent update
to the ADU regulations and identified several
opportunities for clarification and simplification of the
ADU regulations, including:
•Facilitate a one-step review of ADUs at time of
building permit by changing ADUs from a conditional
use to an allowed use subject to specific use
standards
•Expedite review by removing required notice to
adjacent properties
•Provide flexibility of height requirement for existing
structures to be adaptively reused as an ADU
•Clarify need for lockable separation of attached ADUs
•Remove underutilized limited accessory unit type
•Clarify requirements for owner occupancy regarding
limited liability companies and temporary rental
license exemptions
Size Limits
Increase the allowable size of ADUs and remove the
unique floor area definition for ADUs. The new size limits
would be:
•Detached: 800 square feet.
•Attached: 1/2 of the principal structure or 1,000
square feet, whichever is less.
•Affordable or Historic Detached: 1,000 square feet.
•Affordable or Historic Attached: 2/3 of the principal
structure or 1,200 square feet, whichever is less.
Process Improvements
Aside from revised ordinance changes, additional
improvements to the process will be implemented. These
procedural changes will facilitate the one-step review
made possible through the code changes, as well as the
timing of address changes, and creating helpful self-
service handouts and videos for the city website.
Attachment A - Ordinance Summary
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ORDINANCE 8571
AN ORDINANCE AMENDING SECTION 4-20-18, “RENTAL
LICENSE FEE,” TITLE 9, “LAND USE CODE,” AND TITLE 10
“STRUCTURES,” B.R.C. 1981, UPDATING THE
REGULATIONS FOR ACCESSORY DWELLING UNITS; AND
SETTING FORTH RELATED DETAILS
BE IT ORDAINED BY THE CITY COUNCIL OF THE CITY OF BOULDER,
COLORADO:
Section 1. Section 4-20-18, “Rental License Fee,” B.R.C. 1981, is amended to read as
follows:
The following fees shall be paid before the city manager may issue a rental license or
renew a rental license:
(a) Dwelling and Rooming Units: $190 per building.
(b) Accessory Dwelling Units: $190 per unit.
. . .
Section 2. Section 9-2-3, “Variances and Interpretations,” B.R.C. 1981, is amended to
read as follows:
. . .
(d) Board of Zoning Adjustment (BOZA): The BOZA may grant variances from the
requirements of:
. . .
(6) The size requirements for accessory dwelling units of Subsection 9-6-3(n), B.R.C.
1981;
. . .
(i) Floor Area Variances for Accessory Dwelling Units: The BOZA may grant a variance to
the maximum floor area allowed for an attached accessory dwelling unit or for a detached
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accessory dwelling unit under Subsection 9-6-3(n), B.R.C. 1981, only if it finds that the
application satisfies all of the following applicable requirements of either Subparagraph
(i)(1) or (i)(2):
. . .
(2) Unusual Physical Conditions:
(A) That there are unusual physical circumstances or conditions in the design
of the existing structure the accessory dwelling unit would be in, including
without limitation the thickness of exterior walls or framing, that affect the
total allowed interior floor area of the accessory dwelling unit;
. . .
(E) That the accessory dwelling unit would be clearly incidental to the
principal dwelling unit.
. . .
Section 3. Line 4 of Table 4-2: Public Notice Options in Section 9-4-3, “Public Notice
Requirements,” B.R.C. 1981, is amended to read as follows:
(a) Process and Options: When a process or procedure identified in this title requires public
notice, the city manager shall provide such notice according to Table 4-2 of this section.
If a code section does not reference a specific method, the city manager shall determine
the most appropriate notification method to be used.
TABLE 4-2: PUBLIC NOTICE OPTIONS
Public
Notice
Type
Type of Application, Meeting or
Hearing
Mailed Notice Posted Notice
4 Solar exceptions, solar access permits,
accessory units
To adjacent property owners a
minimum of 10 days before final
action
Post property a minimum of 10
days from receipt of application
and prior to final action or any
hearing
. . .
Section 4. The Accessory dwelling unit line under “Residential Uses” of Table 6-1: Use
Table in Section 9-6-1, “Schedule of Permitted Land Uses,” B.R.C. 1981, is amended to read as
follows:
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The schedule in Table 6-1 shows the uses that are permitted, conditionally permitted,
prohibited, or that may be permitted through use review.
. . .
TABLE 6-1: USE TABLE
A = Allowed | C = Conditional Use | U = Use Review | [ ] = Specific Use Standards Apply | - = Prohibited
Zoning District RR-1, RR-2, RE, RL-1 RL-2, RM-2 RM-1, RM-3 RMX-1 RMX-2 RH-1, RH-2, RH-4, RH-5 RH-3, RH-7 RH-6 MH MU-3 MU-1 MU-2 MU-4 BT-1, BT-2 BMS BC-1, BC-2 BCS BR-1, BR-2 DT-4 DT-5 DT-1, DT-2, DT-3 IS-1, IS-2 IG IM IMS P A Specific Use
Standards Use Module R1 R2 R3 R4 R5 R6 R7 R8 MH M1 M2 M3 M4 B1 B2 B3 B4 B5 D1 D2 D3 I1 I2 I3 I4 P A
RESIDENTIAL USES
Residential Accessory
Accessory dwelling unit [CA] [CA] - [CA] [CA] - - - - - - - - - - - - - - - - - - - - [CA] [CA] 9-6-3(n)
. . .
Section 5. Section 9-6-3, “Specific Use Standards - Residential Uses,” B.R.C. 1981, is
amended to read as follows:
(a) Residential Uses:
. . .
(n) Accessory Dwelling Unit:
(1) General Requirements: Three types of accessory units may be approved as
conditional uses: Attached accessory dwelling units, detached accessory dwelling
units, and limited accessory units. The following standards apply to all three types
of an accessory dwelling unit:
(A) General Standards: An accessory dwelling unit shall meet the following
standards:
(i) Lot Limitations: An accessory dwelling unit may be created on a
lot of 5,000 square feet or more with a detached dwelling unit. One
accessory dwelling unit may be located on a lot.
(ii) Maximum Floor Area: The accessory dwelling unit shall be limited
to the floor area in Table 6-3. The board of zoning adjustment may
grant a variance to this floor area requirement pursuant to Section
9-2-3, “Variances and Interpretations,” B.R.C. 1981Occupancy
Requirement: For purposes of determining occupancy
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requirements under Section 9-8-5, “Occupancy of Dwelling
Units,” B.R.C. 1981, the principal dwelling unit and accessory unit
shall be considered one dwelling unit. The occupancy of the
principal dwelling unit together with the occupancy of any
accessory unit shall not exceed the occupancy requirements set
forth in Section 9-8-5, “Occupancy of Dwelling Units,” B.R.C.
1981, for one dwelling unit; provided, however, for purposes of
this section only, any occupant and his or her dependents shall be
counted as one person. The floor area limitation for quarters used
by roomers under Paragraph 9-8-5(a)(1), B.R.C. 1981, shall not
apply to an accessory unit.
Table 6-3: Maximum Floor Area
Accessory Dwelling
Unit
Affordable
Accessory
Dwelling
Unit
Designated
Historic
Property
Attached One-half of the total
floor area of the
principal structure or
1,000 square feet,
whichever is less.
Two-thirds of the total floor
area of the principal structure
or 1,200 square feet,
whichever is less.
Detached 800 sq. ft. 1,000 sq. ft.
(iii) Off-Street Parking: The minimum number of off-street parking
spaces shall be provided on the lot or parcel as required by Table
6-4. The required parking spaces shall meet at least the minimum
dimensional requirements in Table 9-6, “Small Car Parking
Dimension Standards,” B.R.C. 1981, and may be located in a
required landscaped setback abutting the street.
Table 6-4: Off-Street Parking Requirement
(iiv) Owner-Occupied: The principal dwelling unit or accessory
dwelling unit on the parcel or lot must be owner-occupied. The
applicant shall provide evidence to the city manager to
Accessory Dwelling Unit The number of off-street parking spaces
required in the zoning district for the
principal dwelling unit and one
additional off-street parking space
Affordable Accessory
Dwelling Unit
The parking required in the zoning
district for the principal dwelling unit.
Designated Historic
Property
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demonstrate compliance with this requirement at the time of
application or any time thereafter. For entities that are similar to
ownership by a person, such evidence may include without
limitation declaration of trust ownership, articles of organization,
operating agreement, or similar documentation. The city manager
may approve a temporary absence of the owner-occupant for less
than one year with an affidavit of exemption pursuant to the
procedures for temporary rental license exemptions in Section 10-
3-2, “Rental License Required Before Occupancy and License
Exemptions,” B.R.C. 1981.
(iiiv) Rental License: No owner of the property shall allow, or offer to
allow through advertisement or otherwise, any person to occupy
the accessory dwelling unit or the principal dwelling unit as a
tenant or lessee or otherwise for a valuable consideration unless
such rented unit has been issued a valid rental license by the city
manager consistent with the requirements of Chapter 10-3, “Rental
Licenses,” B.R.C. 1981.
(ivvi) Short-Term Rental: Short-term rental of an accessory dwelling unit
and short-term rental of a principal dwelling unit on a lot or parcel
with an accessory dwelling unit are prohibited except as
specifically authorized in Section 10-3-19, “Short-Term Rentals,”
B.R.C. 1981.
(vvii) No Independent Conveyance: No person shall convey an accessory
dwelling unit independently of the principal dwelling unit on the
lot or parcel.
(B) Application: All applicants shall apply on forms provided by the city
manager showing how and in what manner the criteria of this subsection
are met, provide a statement of current ownership and a legal description
of the property, pay the application fee prescribed by Section 4-20-43,
“Development Application Fees,” B.R.C. 1981, and submit plans as may
be required by the manager.
(C) Public Notice: Notice of the application shall be provided consistent with
“Public Notice Type 4,” as defined by Subsection 9-4-3(a), B.R.C. 1981.
(D) Review and Approval: All applications for accessory units shall be
reviewed under the procedures of Section 9-2-2, “Administrative Review
Procedures,” B.R.C. 1981.
(Eviii) Declaration of Use Required: Before obtaining approval, all
owners shall sign a declaration of use, including all the conditions
standards for continued use, to be recorded in the office of the
Boulder County Clerk and Recorder to serve as actual and
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constructive notice of the legal status of the owner’s property. If
the unit is to be an affordable accessory dwelling unit, the
declaration shall include a sworn certification that the unit will
meet the affordability standard and a statement of the number of
bedrooms.
(Fix) Amendments: The owner of an accessory dwelling unit may
amend the approved size, affordability status, or other
characteristics of an approved accessory dwelling unit by filing a
building permit application that demonstrates compliance with
applicable accessory dwelling unit standards. Prior to approval the
owner must sign an updated declaration of use to be recorded in
the office of the Boulder County Clerk and Recorder. The site plan
for an accessory unit may be modified and an affordable accessory
unit may be converted to an accessory unit that is not an affordable
accessory unit provided that an application is filed and reviewed by
the manager under the procedures of Section 9-2-2,
“Administrative Review Procedures,” B.R.C. 1981. The
application must demonstrate that the proposed accessory unit
meets the requirements of this section except that it shall not be
subject to the saturation limitations of Subparagraphs (m)(2)(A)
and (E) and (m)(3)(A) and (E).
(G) Floor Area: For the purpose of calculating the floor area of an attached
accessory unit or detached accessory unit under this subsection (m), floor
area shall mean the total square footage of all levels measured to the
outside surface of the exterior framing, to six inches beyond the interior
wall on an exterior wall, or to the outside surface of the exterior walls if
there is no exterior framing, of a building or portion thereof, which
includes stairways, elevators, the portions of all exterior elevated above
grade corridors, balconies, and walkways that are required for primary or
secondary egress by Chapter 10-5, “Building Code,” B.R.C. 1981, storage
and mechanical rooms, whether internal or external to the structure, but
excluding an atrium on the interior of a building where no floor exists, a
courtyard, the stairway opening at the uppermost floor of a building, and
floor area that meets the definition of uninhabitable space.
(2) Attached Accessory Dwelling Units: In addition to the general accessory unit
standards in Paragraph (mn)(1) of this section, the following standards apply to
attached accessory dwelling units. The owner or the owners of a lot or parcel with
a single-family dwelling unit may establish and maintain an attached accessory
dwelling unit within the principal structure of a detached dwelling unit in the RR,
RE, RL, RMX, A, or P districts if all of the following conditions are met and
continue to be met during the life of the attached accessory dwelling unit:
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(A) Neighborhood Area: In the RL-1 or RL-2 zoning districts, no more than
twenty percent of the lots or parcels in a neighborhood area contain an
accessory unit. For the purpose of this subparagraph:
(i) The “neighborhood area” in RL-1 and RL-2 zoning districts is the
area circumscribed by a line three hundred feet from the perimeter
of the lot line within which any accessory unit will be located.
Within the “neighborhood area” only accessory units within the
RL-1 and RL-2 zoning districts are counted towards the twenty
percent limitation factor.
(ii) For the purpose of calculating the twenty percent limitation factor,
the following shall apply:
a. A legal, nonconforming structure containing two or more
dwelling units is counted as an accessory unit;
b. A cooperative housing unit is counted as an accessory unit;
c. An accessory unit that is licensed as part of a cooperative
housing unit and said cooperative housing unit shall be
counted together as one accessory unit; and
d. The manager may promulgate regulations defining
additional methods to be used in calculating the twenty
percent limitation factor and the neighborhood area.
(iii) If an application for an accessory unit exceeds the twenty percent
requirement set forth in this Subparagraph (m)(2)(A), the manager
will place the applicant on a waiting list for the neighborhood area.
At such time as there is room for an additional accessory unit within a
neighborhood area, the manager will notify the first eligible person on the
waiting list. Such person on the waiting list shall be required to provide
notice of intent to file an application within thirty days and file an
application within sixty days of such notice.
(B) Parking: The attached accessory dwelling unit shall have the following
off-street parking:
(i) The number of off-street parking spaces required in the zoning
district for the principal dwelling unit; and
(ii) One additional off-street parking space on the lot or parcel upon
which the detached dwelling unit is located; and
(iii) The parking spaces required under this Subparagraph (m)(2)(B)
shall not be required to meet the setback requirements of Section
9-7-1, “Schedule of Form and Bulk Standards,” B.R.C. 1981,
provided that the parking spaces are not located in the public right-
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of-way.
(C) Standards: The attached accessory dwelling unit is clearly incidental to the
principal dwelling unit and meets the following standards:
(i) The attached accessory dwelling unit is created only in a single-
family detached dwelling unit on a lot of five thousand square feet
or more.
(ii) The attached accessory dwelling unit does not exceed one-third of
the total floor area of the principal structure or one thousand square
feet, whichever is less, unless a variance is granted pursuant to
Section 9-2-3, “Variances and Interpretations,” B.R.C. 1981.
(A) (iii) Interior Connections: All attached accessory dwelling units shall
be physically separated by a wall or a lockable door. If there is an interior
connection between the attached accessory dwelling unit and the principal
dwelling prior to the creation of the attached accessory dwelling unit, the
connection together with the lockable, physical separation shall be
maintained for the duration during the life of the attached accessory
dwelling unit.
(B) (iv) Side Entrances: Any additional entrance resulting from the creation
of an attached accessory dwelling unit may face the side of the lot fronting
on the street only if such entrance is adequately and appropriately
screened in a manner that does not detract from the single-family
appearance of the principal dwelling unit.
(D) Affordable Accessory Units: If the attached accessory dwelling unit is
licensed as an affordable accessory unit, the following standards apply:
(i) The unit shall only be required to provide the parking required in
the zoning district for the principal dwelling unit.
(ii) The unit may be more than one-third of the total floor area of the
principal structure but shall not exceed one-half of the floor area of
the principal structure or one thousand square feet, whichever is
less. The BOZA may grant a variance to this size requirement
pursuant to Section 9-2-3, “Variances and Interpretations,” B.R.C.
1981.
(iii) If the unit is or will be offered for rental for compensation, the
owner must obtain and at all times thereafter maintain a valid
rental license for an affordable accessory unit issued by the
manager consistent with the requirements of Chapter 10-3, “Rental
Licenses,” B.R.C. 1981.
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(E) Designated Historic Property: If the attached accessory dwelling unit is
located within a principal structure that is designated as an individual
landmark or recognized as contributing to a designated historic district
under Chapter 9-11, “Historic Preservation,” B.R.C. 1981, the following
modifications to the standards of this Paragraph (m)(2) apply:
(i) In the RL-1 and RL-2 zoning district, the unit is not subject to the
twenty percent limitation factor of Subparagraph (m)(2)(A)
provided that no more than thirty percent of the lots or parcels in
the neighborhood area contain an accessory unit;
(ii) The unit shall only be required to provide the parking required in
the zoning district for the principal dwelling unit; and
(iii) The unit may be more than one-third of the total floor area of the
principal structure but shall not exceed one-half of the floor area of
the principal structure or one thousand square feet, whichever is
less. The BOZA may grant a variance to this size requirement
pursuant to Section 9-2-3, “Variances and Interpretations,” B.R.C.
1981.
(3) Detached Accessory Dwelling Units: In addition to the general accessory unit
standards in Paragraph (n)(1) of this section, the following standards apply to
detached accessory dwelling units:An owner or the owners of a lot or parcel with
a single-family detached dwelling unit may establish and maintain a detached
accessory dwelling unit within an accessory structure meeting the size restrictions
described below, on a lot or parcel in the RR, RE, RL, RMX, A, and P districts if
all of the following conditions are met and continue to be met during the life of
the detached accessory dwelling unit:
(A) Maximum Height: The maximum height of accessory buildings with a
detached accessory dwelling unit shall not be greater than twenty feet. The
city manager may modify this height standard if the building meets one of
the followingNeighborhood Area: In the RL-1 and RL-2 zoning districts,
no more than twenty percent of the lots or parcels in a neighborhood area
contain an accessory unit. For the purpose of this subparagraph:
(i) If the roof pitch is 8:12 or greater, provided the building height
does not exceed 25 feet; or The “neighborhood area” in RL-1 and
RL-2 zoning districts is the area circumscribed by a line three
hundred feet from the perimeter of the lot line within which an
accessory unit will be located. Within the “neighborhood area”
only accessory units within the RL-1 and RL-2 zoning districts are
counted towards the twenty percent limitation factor.
(ii) If a legal existing accessory building is converted to a detached
accessory dwelling unit, provided that no changes are proposed to
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the existing accessory building’s height, floor area, or roof
form.For the purpose of calculating the twenty percent limitation
factor, the following shall apply:
a. A legal, nonconforming structure containing two or more
dwelling units is counted as an accessory unit;
b. A cooperative housing unit is counted as an accessory unit;
c. An accessory unit that is licensed as part of a cooperative
housing unit and said cooperative housing unit shall be
counted together as one accessory unit; and
d. The manager may promulgate regulations defining
additional methods to be used in calculating the twenty
percent limitation factor and the neighborhood area.
(iii) If an application for a detached accessory dwelling unit exceeds
the twenty percent requirement set forth in Subparagraph
(m)(3)(A), the manager will place the applicant on a waiting list
for the neighborhood area. At such time as there is room for an
additional accessory unit within the neighborhood area, the
manager will notify the first eligible person on the waiting list.
Such person on the waiting list shall be required to provide notice
of intent to file an application within thirty days and file an
application within sixty days of such notice.
(B) Parking Private Open Space: TheA detached accessory dwelling unit shall
have a minimum of sixty square feet of private open space provided for
the exclusive use of the occupants of the detached accessory dwelling unit.
Private open space may include porches, balconies, or patio areas.the
following parking:
(i) The number of off-street parking spaces required in the zoning
district for the principal dwelling unit; and
(ii) One additional off-street parking space on the lot or parcel upon
which the detached dwelling unit is located;
(iii) The parking spaces required under this Subparagraph (m)(3)(B)
shall not be required to meet the setback requirements of Section
9-7-1, “Schedule of Form and Bulk Standards,” B.R.C. 1981,
provided that the parking spaces are not located in the public right-
of-way. To the extent practical, any additional off-street parking
that is constructed in the RR or RE zoning district required for the
detached accessory dwelling unit shall be screened from the view
of properties that directly abut a property line of the detached
accessory dwelling unit.
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(C) Incidental to Principal Dwelling Unit: The detached accessory dwelling
unit is clearly incidental to the principal dwelling unit and meets the
following standards:
(i) The detached accessory dwelling unit is created on a lot of five
thousand square feet or larger.
(ii) The detached accessory dwelling unit’s floor area does not exceed
five hundred and fifty square feet, unless a variance is granted
pursuant to Section 9-2-3, “Variances and Interpretations,” B.R.C.
1981.
(iii) The following design standards apply to detached accessory
dwelling units:
a. Maximum height of accessory buildings with a detached
accessory dwelling unit shall not be greater than twenty
feet unless the roof pitch is greater than 8:12 and the
resulting ratio of the height of the roof (measured from the
eave line to the top of the roof) to the height of the side
walls (measured from the low point of grade to the eave
line) is less than a 1:2 ratio. The city manager may modify
this height standard for a legal existing accessory building
that is being converted to a detached accessory dwelling
unit to the extent that the existing accessory building's
height and size is not proposed to be modified. In no case
may a building height exceed twenty-five feet.
b. A detached accessory dwelling unit shall have a minimum
of sixty square feet of private open space provided for the
exclusive use of the occupants of the detached accessory
dwelling unit. Private open space may include porches,
balconies, or patio areas. Decks, porches, patios, terraces,
and stairways, located at a height greater than thirty inches
above grade, shall be considered part of the building
coverage.
c. Setbacks shall comply with accessory building setbacks.
Where the rear yard of a property in the RR or RE zoning
district directly abuts an RL zoning district, the rear yard
accessory building setback shall be the same as the side
yard setback for accessory buildings for applicable RR or
RE zoning districts.
(D) Affordable Accessory Units: If the detached accessory dwelling unit is
licensed as an affordable accessory unit, the following standards apply:
(i) The unit shall only be required to provide the parking required in
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the zoning district for the principal dwelling unit.
(ii) The unit’s floor area may be up to eight hundred square feet. The
BOZA may grant a variance to this size requirement pursuant to
Section 9-2-3, “Variances and Interpretations,” B.R.C. 1981.
(iii) If the unit is or will be offered for rental for compensation, the
owner must obtain and at all times thereafter maintain a valid
rental license for an affordable accessory unit issued by the
manager consistent with the requirements of Chapter 10-3, “Rental
Licenses,” B.R.C. 1981.
(E) Designated Historic Property: If either the accessory structure the
detached accessory dwelling unit is located in or the principal structure on
the lot or parcel is designated as an individual landmark or recognized as
contributing to a designated historic district under Chapter 9-11, “Historic
Preservation,” B.R.C. 1981, the following modifications to the standards
of this Paragraph (m)(3) apply:
(i) In the RL-1 and RL-2 zoning district, the unit is not subject to the
twenty percent limitation factor of Subparagraph (m)(3)(A)
provided that no more than thirty percent of the lots or parcels in
the neighborhood area contain an accessory unit;
(ii) The unit shall only be required to provide the parking required in
the zoning district for the principal dwelling unit; and
(iii) The unit’s floor area may be up to one thousand square feet. The
BOZA may grant a variance to this size requirement pursuant to
Section 9-2-3, “Variances and Interpretations,” B.R.C. 1981.
(4) Limited Accessory Units: In addition to the general accessory unit standards in
Paragraph (m)(1) of this section, the following standards apply to limited
accessory units that may be approved as a conditional use in the RR-1, RR-2, RE,
and RL-1 Zoning Districts only. An existing nonconforming duplex or two
detached dwelling units located on the same lot and within the R1 use module
may be converted to limited accessory dwelling units. A limited accessory
dwelling unit may be modified and expanded as a conditional use. Conversion to
a limited accessory dwelling unit is subject to compliance with all of the
following standards:
(A) Applicability: This Subparagraph (m)(4) is only applicable to dwelling
units that legally existed, were actively used as multiple dwelling units,
and had a valid rental license on January 1, 2005.
(B) Expansion Limitation: The cumulative total of any expansion shall not
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exceed twenty percent of the total floor area that was documented at the
time of the initial expansion. Any expansion of the restricted accessory
unit shall not exceed ten percent. In no case shall any expansion cause the
cumulative size of the restricted dwelling units to exceed the maximum
allowable floor area ratio of the underlying zoning district as set forth in
Section 9-8-1, “Schedule of Intensity Standards,” B.R.C. 1981.
(C) Parking: The minimum number of off-street parking spaces shall not be
less than three spaces. All parking shall comply with the design and access
requirements set forth in Section 9-9-6, “Parking Standards,” B.R.C. 1981.
A minimum of one off-street parking space shall be available for use by
the restricted accessory dwelling unit.
(D) Loss of Prior Nonconforming Status: If a nonconforming duplex or two
detached dwelling units are converted to limited accessory units through
the conditional use process, any prior nonconforming status is lost.
Section 6. Section 9-8-5, “Occupancy of Dwelling Units,” B.R.C. 1981, is amended to
read as follows:
. . .
(b) Attached Accessory Dwelling Unit, Detached Accessory Dwelling Unit, or Limited
Accessory Dwelling Unit: The occupancy of an attached accessory dwelling unit,
detached accessory dwelling unit, or limited accessory dwelling unit must meet the
requirements of Subsection 9-6-3(n), B.R.C. 1981. The principal dwelling unit and
accessory dwelling unit shall be considered one dwelling unit. The occupancy of the
principal dwelling unit together with the occupancy of any accessory dwelling unit shall
not exceed the occupancy requirements set forth in this section for one dwelling unit;
provided, however, for purposes of this subsection only, any occupant and his or her
dependents shall be counted as one person. The floor area limitation for quarters used by
roomers under Paragraph 9-8-5(a)(1), B.R.C. 1981, shall not apply to an accessory
dwelling unit.
. . .
(d) Cooperative Housing License: A dwelling unit licensed as a cooperative housing unit
pursuant to Section 10-11-3, “Cooperative Housing Licenses,” B.R.C. 1981, shall not be
subject to the occupancy limits or any exceptions as set forth in this section; and an
attached accessory dwelling unit or detached accessory dwelling unit licensed with such
dwelling unit as a cooperative housing unit shall not be subject to the occupancy
standards of SubpParagraph 9-6-3(n)(1)(A)(ii), “Occupancy Requirement”9-8-5(b),
“Accessory Dwelling Unit,” B.R.C. 1981. All such dwelling units together with any
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attached accessory dwelling unit or detached accessory dwelling unit so licensed shall be
limited to no fewer than four occupants with the maximum number of occupants, without
regard to whether the occupants are related or not, as follows:
. . .
Section 7. Row six under “Use” of Table 9-2: Use Specific Motor Vehicle Parking
Requirements for Residential Uses in all Zones and row three under “Residential Uses” of Table
9-8: Off-Street Bicycle Parking Requirements in Section 9-9-6, “Parking Standards,” B.R.C.
1981, are amended to read as follows:
. . .
(b) Off-Street Parking Requirements: The number of required off -street motor vehicle
parking spaces shall be provided in Tables 9-1, 9-2, 9-3, and 9-4 of this section; the
number of required off-street bicycle parking spaces shall be provided in Table 9-8 of
this section:
. . .
(2) Use Specific Motor Vehicle Parking Requirements for Residential Uses:
TABLE 9-2: USE SPECIFIC MOTOR VEHICLE PARKING REQUIREMENTS FOR
RESIDENTIAL USES IN ALL ZONES
Use Parking Requirement
Roomers within a single-unit dwelling 1 space per 2 roomers
Residential developments in which 1-bedroom
units are 60 percent or more of the total
1.25 spaces per 1-bedroom unit
Rooming house, boarding house, fraternity,
sorority, group living, and hostels
2 spaces per 3 occupants
Efficiency living units, transitional housing 1 space per DU
Bed and breakfast 1 space per guest room + 1 space for operator or
owner's DU within building
Attached aAccessory dwelling unit, detached
accessory dwelling unit
The off-street parking requirement for the
principal DU must be met, plus any parking space
required for the accessory dwelling unit, see
Subsection 9-6-3(n), B.R.C. 1981
. . .
(g) Bicycle Parking:
(1) Required Bicycle Spaces: Bicycle parking spaces must be provided as required by
Table 9-8 of this section.
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TABLE 9-8: OFF-STREET BICYCLE PARKING REQUIREMENTS
Use Type (based on Table 6-1
of Section 9-6-1
Minimum Number of Off-
Street Bicycle Spaces
Long-Term Short-Term
Residential Uses
Dwelling units(a) with a private
garage(b)
no requirement n/a n/a
Dwelling units without a private
garage(b)
2 per unit 75% 25%
Accessory dwelling units no requirement n/a n/a
. . .
Section 8. Section 9-16-1, “General Definitions,” B.R.C. 1981, is amended to read as
follows:
(a) The definitions contained in Chapter 1-2, “Definitions,” B.R.C. 1981, apply to this title
unless a term is defined differently in this chapter.
. . .
(c) The following terms as used in this title have the following meanings unless the context
clearly indicates otherwise:
. . .
Accessory dwelling unit means a separate and complete single housekeeping unit within a
detached dwelling unit or within an accessory structure to the principal dwelling unit of
the lot or parcel upon which the unit is located, permitted under the provisions of
Subsection 9-6-3(n), B.R.C. 1981.
. . .
Affordable accessory dwelling unit means a unit for which the rents meet the affordability
standard.
. . .
Attached accessory dwelling unit means a separate and complete single housekeeping
unit within a detached dwelling unit, permitted under the provisions of Subsection 9-6-
3(m), B.R.C. 1981.
. . .
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Designated historic property means a property with a building designated as an
individual landmark or recognized as contributing to a designated historic district under
Chapter 9-11, “Historic Preservation,” B.R.C. 1981.
. . .
Detached accessory dwelling unit means a separate and complete single housekeeping
unit within an accessory structure to the principal dwelling unit of the lot or parcel upon
which the unit is located that is permitted under the provisions of Paragraph 9-6-3(n)(3),
B.R.C. 1981.
. . .
Limited accessory unit means an existing nonconforming duplex or two detached
dwelling units located on the same lot and within the R1 use module that has been
approved in compliance with the standards in Section 9-6-3(n)(4).
. . .
Owner-occupied means a dwelling unit or accessory dwelling unit that is the principal
residence of at least one owner of record of the lot or parcel upon which the dwelling unit
or accessory dwelling unit is located, who possesses at least an estate for life, or a fifty
percent fee simple ownership interest, or is the trustor of a revocable living trust., or is
the member that owns at least fifty percent of a limited liability company, or is the
partner that owns at least fifty percent of a partnership or limited liability partnership, or
similar entity.
. . .
Section 9. Section 10-1-1, “Definitions,” B.R.C. 1981, is amended to read as follows:
(a) The following terms used in this title have the following meanings unless the context
clearly indicates otherwise:
. . .
Accessory dwelling unit means an accessory dwelling unit permitted under Section 9-6-
3(n), “Accessory Dwelling Units,” B.R.C. 1981.
. . .
Section 10. Section 10-3-6, “License Application Procedure for Buildings Converted to
Rental Property,” B.R.C. 1981, is amended to read as follows:
Every operator converting a property to rental property shall follow the procedures in this
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section for procuring a rental license:
(a) Submit to the city manager a complete application packet, on forms provided by the
manager, at least thirty days before rental of the property including:
. . .
(4) If the unit is an affordable accessory dwelling unit as defined in Section 9-16-1,
“General Definitions,” B.R.C. 1981, a sworn certification that the unit will meet
the rental affordability standard as defined in Section 9-16-1, “General
Definitions,” B.R.C. 1981.
. . .
Section 11. Section 10-3-7, “License Renewal Procedure for Buildings Occupied as
Rental Property,” B.R.C. 1981, is amended to read as follows:
Every operator of a rental property shall follow the procedures in this section when
renewing an unexpired license:
(a) Submit to the city manager a complete application packet, on forms provided by the
manager including:
. . .
(4) If the unit is an affordable accessory dwelling unit as defined in Section 9-16-1,
“General Definitions,” B.R.C. 1981, a sworn certification that the unit will meet
the rental affordability standard as defined in Section 9-16-1, “General
Definitions,” B.R.C. 1981.
. . .
Section 12. Section 10-3-16, “Administrative Remedy,” B.R.C. 1981, is amended to read
as follows:
(a) If the city manager finds that a violation of any provision of this chapter or Chapter 10-2,
“Property Maintenance Code,” B.R.C. 1981, exists, the manager, after notice to the
operator and an opportunity for hearing under the procedures prescribed by Chapter 1-3,
“Quasi-Judicial Hearings,” B.R.C. 1981, may take any one or more of the following
actions to remedy the violation:
(1) Impose a civil penalty according to the following schedule:
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(A) For any violation in the following areas or of affordability standards: The
area south of Arapahoe Avenue, north of Baseline Road, east of 6th Street
and west of Broadway, the area south of Baseline Road, north of Table
Mesa Drive, east of Broadway and west of U.S. Route 36 and the area
south of Canyon Boulevard, north of Arapahoe Avenue, west of Folsom
Street and east of 15th Street or for any violation of affordability standards
for an affordable accessory dwelling unit approved under Subsection 9-6-
3(n), B.R.C. 1981:
. . .
(b) If the city manager finds that an affordable accessory dwelling unit was advertised,
offered for rent or rented for an amount in excess of the affordability standard, in addition
to the actions the manager may take under subsection (a), the manager shall impose a
penalty equal to the amount charged in excess of the affordability standard during the
term of the license, plus interest at the rate of twelve percent per annum, and shall pay
such funds collected to the tenant who was charged in excess of the affordability
standard.
. . .
Section 13. Section 10-3-19, “Short-Term Rentals,” B.R.C. 1981, is amended to read as
follows:
(a) Short-term rentals are prohibited unless the city manager has issued a valid short -term
rental license for the property.
. . .
(o) An accessory dwelling unit or a principal dwelling unit on a single-family lot or parcel
with an accessory unit may not be rented as a short-term rental unless all the following
requirements are met:
(1) Both the accessory dwelling unit and the principal dwelling unit were legally
established on the effective date of Ordinance No. 8256by February 1, 2019;
(2) A current and valid short-term rental license exists for the unit;
(3) If the accessory dwelling unit is licensed for short-term rental, only the accessory
dwelling unit and not any other dwelling unit on the same property may be
licensed or used as a rental;
(4) If a principal dwelling unit is licensed for short-term rental, then no accessory
dwelling unit on the same property may be licensed or used as a rental;
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(5) An accessory dwelling unit may not be rented as a short-term rental for more than
one hundred twenty days in any calendar year;
(6) Notwithstanding the provisions of subsection (i), the occupancy of the accessory
dwelling unit and the principal dwelling unit must meet the requirements of
Subsection 9-68-35(nb)(1), B.R.C. 1981; and
(7) Licensing Limitations and Requirements:
(A) After February 1, 2019, Nno application for a new short-term rental
license shall may be accepted. on or after the effective date of Ordinance
No. 8256. On or after the effective date of Ordinance No. 8256, a new
short-term rental license may be issued only for complete applications
received by the city manager on or before the effective date of Ordinance
No. 8256. On or after the effective date of Ordinance No. 8256, the The
city manager may renew unexpired short-term rental licenses pursuant to
Section 10-3-7, “License Renewal Procedures for Buildings Occupied as
Rental Property,” B.R.C. 1981. A license for which a complete renewal
application is not filed within ninety days from the expiration date shall be
considered expired.
. . .
Section 14. Section 10-11-3, “Cooperative Housing Licenses,” B.R.C. 1981, is amended
to read as follows:
(a) License terms shall be as follows:
. . .
(l) Any attached accessory dwelling unit or detached accessory dwelling unit to a dwelling
unit that is licensed pursuant to this chapter shall be part of the licensed cooperative
housing unit and subject to the standards of this chapter. The occupants of the dwelling
unit and accessory unit shall all be members of the cooperative. While such units are
licensed as a cooperative housing unit under this chapter, neither the principal dwelling
unit nor the accessory dwelling unit shall be required to be owner-occupied as would
otherwise be required under Subparagraph 9-6-3(n)(1)(A)(iv), “Owner-Occupied,”
B.R.C. 1981.
. . .
Section 15. Tables 6-3 and 6-4 are added to Section 9-6-3, “Specific Use Standards –
Residential Uses,” B.R.C. 1981, by this ordinance. The City Council amends the Boulder Revised
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Code by renumbering the subsequent tables in Chapter 9-6, “Use Standards,” B.R.C. 1981,
together with all associated references and cross references to the renumbered tables in the Boulder
Revised Code.
Section 16. This ordinance shall apply to any building permit, conditional use, use review,
and site review applied for on or after September 1, 2023. Any project for which a complete
building permit, site review, use review, or conditional use application has been submitted to the
city or which has received a site review, use review, or conditional use approval prior to the
effective date of this ordinance for a use inconsistent with the provisions of this ordinance will be
permitted to establish the proposed use under the use standards of Chapter 9 -6, “Use Standards,”
B.R.C. 1981, in effect at the time the building permit, site review, use review, or conditional use
application was submitted to the city. Such applicants shall be required to pursue such development
approvals and meet all requirements deadlines set by the city manager and the Boulder Revised
Code necessary to establish the proposed use. The applications for such project shall demonstrate
compliance with all applicable laws. Any failure to meet the requirements of the city manager or
this section of this ordinance will result in a denial of such application. Any subsequent application
shall meet the requirements in place at the time of such subsequent application.
Section 17. If any section, paragraph, clause, or provision of this ordinance shall for any
reason be held to be invalid or unenforceable, such decision shall not affect any of the remaining
provisions of this ordinance.
Section 18. This ordinance is necessary to protect the public health, safety, and welfare
of the residents of the city and covers matters of local concern.
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Section 19. The City Council deems it appropriate that this ordinance be published by
title only and orders that copies of this ordinance be made available in the office of the city clerk
for public inspection and acquisition.
INTRODUCED, READ ON FIRST READING, AND ORDERED PUBLISHED BY
TITLE ONLY this 20th day of April 2023.
______________________________
Mark Wallach,
Mayor Pro Tem
Attest:
________________________________
Emily Richardson,
Deputy City Clerk
READ ON SECOND READING, PASSED AND ADOPTED this 4th day of May 2023.
_____________________________
Mark Wallach,
Mayor Pro Tem
Attest:
_______________________________
Emily Richardson,
Deputy City Clerk
Accessory Dwelling Units in Boulder
Examples of ADUs Approved Since 2019
Detached
Street and alley views: Lots with alley access
721 Concord Ave | RL-1 | 8,689 sf lot
718 sf
717 University Ave | RL-1 | 12,765 sf lot
800 sf
2875 6th St | RL-1 | 6,173 sf lot
516 sf
750 14th St | RL-1 | 6,227 sf lot
835 sf
903 Pine St | RL-1 | 10,107 sf lot
800 sf
2610 Pine St | RMX-1 | 7,000 sf lot
681 sf
3225 6th St | RL-1 | 9,837 sf lot
800 sf
835 Pine St | RL-1 | 9,807 sf lot
500 sf
This document is intended to show a variety of sizes and styles of recently approved and constructed ADUs.
Attachment H - Photos
Detached
Street views: Lots without alley access
1290 Hartford Dr | RL-1 | 7,082 sf lot
835 sf
Attached
Street views
2266 Edgewood Dr | RL-1 | 7,715 sf lot
563 sf
431 Arapahoe Ave | RL-1 | 10,462 sf lot
669 sf
5045 Cascade Ave | RE | 17,686 sf lot
800 sf
660 Juniper Ave | RR-2 | 15,050 sf lot
799 sf
880 35th St | RL-1 | 7,562 sf lot
480 sf
3530 Everett Dr | RL-1 | 7,480 sf lot
1200 sf*
720 Willowbrook Rd | RE | 11,630 sf lot
1550 sf*
300 19th St | RL-1 | 7,396 sf lot
769 sf
3560 19th St | RL-1 | 5,477 sf lot
1062 sf*
3875 Cloverleaf Dr | RE | 10,711 sf lot
695 sf
450 S 41st St | RL-1 | 6,827 sf lot
812 sf
* Floor area variance approved by Board of Zoning Adjustment
Attachment H - Photos