ACCESSORY DWELLING
UNITS DESIGN GUIDE
A handbook for building accessory dwelling units in Tacoma
CITY OF TACOMA
ADU in Tacoma, WA. Photo Credit: Lauren Flemister.
City of Tacoma
747 Market Street, Tacoma, WA 98402
http://www.cityoftacoma.org
May 1, 2019
I am pleased to oer this guide to assist in understanding Accessory Dwelling Unit (ADU) standards, the
permit process, and practical considerations. Navigating the permit and construction process can be
complex, and people need information to make big decisions about their home and property. We look
forward to helping you evaluate whether building an ADU makes sense for your household.
ADUs are intended to provide exibility to homeowners, to increase the range of housing options
and price points, and to t with neighborhood patterns. Whether you are motivated by the desire for
companionship, an income stream, housing a relative or caregiver, or other reasons, building an ADU may
be a viable option.
ADUs are not a new concept. However, in most of Tacoma’s neighborhoods, ADUs have been allowed only
when attached to or within the main house. Over time, many people contacted the City to express interest
in making ADUs more broadly available.
On March 18, 2019 the City Council adopted changes to Tacoma’s ADU standards intended to do just
that. One of the biggest changes was allowing Detached ADUs (backyard cottages) throughout our City’s
neighborhoods. In addition, the Council made updates intended to reduced barriers and streamline the
permitting process.
The City also adopted land use and design standards to ensure that ADUs are well-built, t with the scale
of the neighborhood, continue yard patterns, and clearly accessory to the main house.
Moving forward, the City Council will revisit Tacoma’s ADU standards to ensure that they are working as
intended. This guide will be updated accordingly, and we will add further information as we learn more.
We sincerely wish that ADUs will help meet both your household’s needs, and the broader community’s
goals for a livable, sustainable and aordable city.
Peter Human, Planning and Development Services Director
1 - A D U D E S I G N G U I D E
Table of Contents
INTRODUCTION
ADU Submittal And Review Process
» What Is An ADU 2
» Where ADUs Are Allowed 2
» Types Of ADUs 3
» Legalization Of Unpermitted ADUs 3
» Code Citations 4
» How To Apply For An ADU 4
» Submittal Documents 4
» City Permit And Utility Fees 5
ADU Land-Use Standards
» ADU Size 6
» Setbacks And Location 6
» Height 7
» Parking 7
» Design Standards For All ADUs 8
» Design Standards For Detached ADUs 11
» Open Space 11
» Walkways 11
» Addressing 11
» Detached ADU’s + Accessory Structures 12
ADU Building And Utilities Standards
» Construction Requirements For All ADUs 13
» Converting An Existing Space Or Building 14
» Specic Standards For Attached ADUs 15
» Legalization Of Nonconforming ADUs 15
» Subdividing Property With A DADU 16
» Utilities For ADUs 16
Additional Resources
» Submittal Checklist For New Construction
» Submittal Checklist For Conversion Or Addition
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A D U D E S I G N G U I D E - 2
This section provides an overview of the practical considerations in deciding whether and how to build an
ADU. It includes a discussion of where ADUs are allowed and the things to consider with dierent types of
ADUs. It also summarizes the City’s permit review process.
What is an Accessory Dwelling Unit (ADU)?
An ADU is a second, smaller dwelling unit located on the same lot as a single-family dwelling. ADUs are
intended as a housing option that can contribute to housing aordability and choice, respond to changing
household needs and lifestyles, add housing supply, and contribute to neighborhood stability, in a manner
that is consistent with residential neighborhood patterns. ADUs can be located either within or attached
to the primary residence, or in a detached structure in the rear yard. Both dwellings must be in single
ownership. ADUs cannot be sold or owned separately from the main dwelling.
Accessory dwelling unit. A second subordinate dwelling unit located on the same lot as a single-
family dwelling (hereinafter referred to as the “main dwelling”) and either within the same building
as the main dwelling or in a detached building, with a provision for independent cooking, living,
sanitation, and sleeping (TMC 13.06.700)
Where ADUs are allowed?
A few simple rules govern where ADUs are allowed within the City of Tacoma:
• ADUs are generally permitted in the same zoning districts that permit single-family development.
Specically, ADUs are permitted in all zoning districts, except shoreline districts and most industrial
districts.
• There must be a house (single-family dwelling) on the parcel. ADUs are not allowed on vacant lots,
with 2-family, 3-family, multifamily or with other land uses.
• Only one ADU is allowed per parcel.
• ADUs are allowed on all legally established parcels. There is no minimum lot size or width.
• ADUs must be designed and constructed to meet the applicable development standards.
FRONT YARD
MAIN HOUSE
BUILDING
AREA
REAR YARD
DADU
SIDE SETBACK
STREET
ALLEY
Example of typical lot with detached
accessory dwelling unit
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ADU
SUBMITTAL + REVIEW PROCESS
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Types of ADUs
There are many ways to design and build ADUs. The options may be
shaped by the existing structures, yard space, proximity of utilities, City
regulations, and your personal objectives and budget. Deciding how to
build your ADU aects construction cost as well as how you will inhabit
and experience your house, the ADU, and yard.
There are two general types of ADUs—Attached and Detached.
Attached ADUs are located within or attached to the primary residence.
An Attached ADU could be created entirely within the existing walls
of your house (for example, as a basement or attic conversion). Or, an
Attached ADU could involve an addition to the house (such as adding a
story or extending the house into the rear yard).
Detached ADUs are separate structures located in the rear yard of the
main dwelling. Detached ADUs could be constructed as a completely
new structure. Or, the ADU could be a conversion and/or addition to
an existing accessory structure (such as adding a second story to, or
converting, a garage).
These variables aect the building, land use and utility regulations,
scope of work, and budget.
Legalization of unpermitted ADUs
The City is encouraging owners of existing, unpermitted ADUs to
legalize them by obtaining permits. For a limited time, the City is oering exibility on ADU standards
(including size, height, setback and design) that would otherwise apply. To be eligible, the ADU and site
must consist of:
• No more than one ADU per residential lot
• Be located within the main dwelling or as a detached structure in the rear yard
• Not exceed maximum occupancy under the Building Code
• Include facilities for cooking, living, sanitation, and sleeping
• Provide an address visible from the street
• Be consistent with the City’s Home Occupation and Short-term Rental standards
• Meet the Minimum Housing Code standards set forth in Section 2.01 of the Building Code
Applications must be submitted by December 31, 2020 to receive this exibility. After January 1, 2021,
owners of illegal ADUs shall be subject to the enforcement provisions of TMC 13.05.100. and 13.02.01
Photo credit: Bob + Kenny Harris ADU, https://accessorydwellings.org
Top: Attached Accessory Dwelling Unit
Bottom: Detached Accessory Dwelling
Unit
Photo Credit: Rainbow Valley Construction
SUBMITTAL + REVIEW PROCESS
ADU
A D U D E S I G N G U I D E - 4
Code Citations
This guide illustrates the most pertinent sections of the Tacoma Municipal Code (TMC), including the
following:
• TMC 13.06.150 Accessory dwelling units.
• TMC 13.06.100.D Residential districts - Lot size and building envelope standards.
• TMC 13.06.100.F Accessory building standards.
• TMC Title 2 Buildings.
Consult City sta to determine whether other standards apply. In the case of any conict, the TMC
language shall control.
How to apply for an ADU
1. To start, prepare a Building Permit application. In addition, Site Development, Fire, Electrical, Water
Plumbing and/or Mechanical permits may be required. There is no separate permit required for
ADUs.
2. Online application: Submit permit applications online at www.tacomapermits.org. Select the
“Applying for Permits” tab, create an account, select the type of permit, complete the application
process/questions and upload required documents.
3. In person application: Apply in person at Planning and Development Services (PDS), Tacoma
Municipal Building, 747 Market Street – 3rd Floor, Tacoma WA.
4. If revisions are required, provide revised plans and include a written response to each comment
that references the plan pages being revised. Then, upload the documents via the “submitting plan
revisions” option or bring them in person to the PDS oce.
5. Current plan review times can be accessed at tacomapermits.org.
Submittal Documents
To apply for ADU permits, included the following (documents must be submitted per Tacoma’s electronic
le standards).
• Completed ADU submittal checklist.
• Written scope of work identifying the proposed work areas, ADU square footage, square footage
of primary dwelling unit, height of detached ADU, location, cost/value of the work and, if a
remodel, an itemized cost estimate.
• Site plan, drawn to scale, showing the existing and proposed buildings, building setbacks to
property lines, distances between all structures, existing and proposed utilities, walking
paths, existing and proposed parking, and new and existing impervious surfaces since
January 1, 2003.
• Floor plans, drawn to scale, of existing building footprint and proposed primary and accessory
dwelling units.
• A completed Building Permit application (ADU-BLDRN):
▫ For new structures, review tip sheet for new single family dwellings combination permit.
▫ For remodels or converted buildings, review tip sheet for remodels and additions.
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ADU
SUBMITTAL + REVIEW PROCESS
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City permit and utility fees
The cost of permits depends on factors including the size of the new structure or addition, and/or cost of
remodel/conversion associated with the (D)ADU, what utilities are included, and other factors. To obtain
an estimation of permit fees associated with the project, the use of our Fee Estimator Tool is encouraged
(available at www.tacomapermits.org). When calculating fees for the purpose of estimating permitting
costs, be sure to combine costs of all associated permits. Please note that separate utility fees (through
Tacoma Public Utilities) will also apply.
For more information
Contact Planning and Development Services at (253) 591-5030 or visit www.tacomapermits.org.
SUBMITTAL + REVIEW PROCESS
ADU
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This section summarizes land use and design standards that typically
apply to ADUs. Building and utilities standards are addressed in Section
3. Consult City sta to determine whether other standards may apply.
ADU Size
The size of ADUs (both Attached and Detached) is measured in
habitable/living area. The habitable area of the ADU, excluding any non-
living areas, is limited to the most restrictive of the following:
1. No more than 15% of
the lot area.
2. No more than 85%
of the living
area of
the primary structure
or dwelling.
3. No more than 1,000
square feet.
NOTE: Detached ADUs are considered a type of accessory structure
under Tacoma’s code. However, ADU size is calculated dierently
than other types of accessory structures. For sites with more than one
accessory structure, if one of them is a Detached ADU, an additional
500 square feet may be added to the total square footage of accessory
structure footprints. This does not increase the permitted size of the
ADU. For more information, see TMC 13.06.100.F.
Setbacks & location.
Attached ADUs are part of the primary structure and are subject to the
primary structure setbacks.
Setbacks are dierent in dierent zoning districts. In the R-2 District, the
most common residential district, primary structure setbacks (measured
from property lines) are:
• Front: 20 feet
• Side: 5 feet
• Rear: 25 feet, measured from the mid-point of an alley, if present
• Contact Tacoma Permits to learn the setbacks in your location
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ADU
DEVELOPMENT STANDARDS
Detached ADU
Attached ADU
ADU SF
=/<
15% of Lot SF
OR
ADU SF
=/<
85% of
House SF
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DEVELOPMENT STANDARDS
ADU
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Detached ADUs must be located as follows:
• On the same lot as the primary structure.
• In the rear yard (behind the rear wall) of the primary structure.
• A minimum of 5 feet from side and rear property lines, except no
setback is required from alleys.
• Meet re separation standards, per the Building Code, in
one of the following ways.
▫ Provide a minimum 10 foot separation between the ADU
and any other structure; or,
▫ If closer than 10 feet, re separation rated
construction will be required, per standards.
ADU Height
Attached ADUs are part of the primary structure, and are subject to the
primary structure height limits. In most residential districts, the maximum
height is 35 feet, measured to the midpoint of the roof. In View Sensitive
Districts, the maximum height is 25 feet, measured to the peak of the roof.
Detached ADUs shall be no taller than the main house and the most
restrictive of the following:
• Up to 18 feet measured to the midpoint of a peaked roof.
• Up to 20 feet with incorporation of parking, or with Built Green
4 stars (or equivalent) environmental certication.
• Conversion of an existing accessory structure taller than 18 feet
may be considered as a Conditional Use.
• In View Sensitive Districts, the maximum height is 15 feet to the
peak of the roof (measured per TMC 13.06.700.B). Additional
height, if proposed, would be considered subject to TMC 13.06.645
variance criteria.
•
Parking
Parking is not required for ADUs. If parking is proposed, it must be located
in and accessed from the rear portion of the lot. The addition of an ADU
may not remove parking required for the primary dwelling (typically, two
stalls are required for the main house).
18’-0” 15’-0”
DADU
midpoint of
roof plane
DADU
VIEW SENSITIVE DISTRICTS
HEIGHT OF DADU *
top of
structure
ADU Hight Requirements
* When parking is incorporated
the Structure can be up to 20’
A D U D E S I G N G U I D E - 8
Design Standards for all ADUs
Both attached and detached ADUs are required to meet the
following standards.
1. Design all facades to respond to the conditions of the site
2. Locate the ADU to minimize the visual prominence of the
structure and its contrast to the main house
3. Select materials and details to withstand weather/wear regardless
of architectural style
4. Meet applicable Historic District design standards. Historic review
is required for development activities in historic
districts designated by the City of Tacoma. For more information,
visit www.cityoftacoma.org/historicpreservation.
5. ADU’s must be designed to t in with the fabric of the
neighborhood by either option A or option B as described below
Generally matching the exterior architectural
style,appearance and character of the main house with
similar materials, window, facade and roof design; or
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Objective: demonstrate clear relationship with main structure or
neighborhood.
To meet the criteria for 1-A, the ADU design must demonstrate that
it is visually secondary to the existing house; it has the same window
and door patterns, scale and orientation; the same nishes, materials,
material application, detail and quality; and the same pitch, materials
and details for the roof.
ADU
DEVELOPMENT STANDARDS
Photo credit: Candace Kramer DADU, https://accessorydwellings.org
Example (photos):
Photos: Both DADU’s match the roof
details, materials, and pitch of the
main house. Though other features
of the DADU have subtle dierences,
the consistency of the two structure
make them good examples that
appears to satisfy the requirements
of 1-A.
A
OPTION
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DEVELOPMENT STANDARDS
ADU
Complement the main house through use of materials and
design of equal or better quality generally matching the
exterior architectural style, appearance and character of the
main house with similar materials, window, facade and roof
design
Complement Main House:
The City will conduct an administrative review to determine if the design
complements the primary home. The criteria for this review is as follows.
All projects must show compliance with (at minimum) Visual Hierarchy
and two of the three listed other criteria (Facade, Windows + Doors,
Roof);
Visual Hierarchy:
ADU’s will be required to appear secondary to the main house and
generally consistant with the existing neighborhood pattern by following
these criteria:
• Organize the massing of the ADU to mitigate visual impact
• Blend with existing structure if attached
Facade:
Objective: demonstrate clear relationship with main structure or
neighborhood through:
• Relationship between nishes (e.g. same color)
• Relationship between materials (e.g. both wood)
• Relationship between application (e.g. both lapped)
Windows + Doors:
Objective: demonstrate clear relationship with main structure or
neighborhood through:
• Relationship between patterns (e.g. divided lite)
• Relationship of scale (e.g. same size or proportion)
• Relationship of orientation (e.g. portrait v. landscape)
Roof:
Objective: demonstrate clear relationship with main structure or
neighborhood:
• Relationship between pitches (e.g. both 2:12)
• Relationship between materials (e.g. wood shingle) Relationship
between details (e.g. rafter tails, gable braces)
B
OPTION
A D U D E S I G N G U I D E - 10
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ADU
DEVELOPMENT STANDARDS
Photo credit: Kendra and Victor Duong DADU, https://accessorydwellings.org
Photo credit: Bob and Kenny Harris ADU, https://accessorydwellings.org
Windows and Doors
Photos: (left) the DADU’s windows
and doors are not consistent with
the house. For example, the action
of the windows, the material they
are constructed from, and their
orientation are not consistent.
(right) though not the same, the
windows on the ADU have the same
divided lite pattern as the house
Photo credit: Stew Hulick DADU, https://accessorydwellings.org Photo credit: Bruce DADU, https://accessorydwellings.org
Roofs
Photos: (left) The DADU matches
the roof details, materials, and pitch
though other features of the DADU
are clearly dierent.
(right, two photos) the main house
is a pitched roof and the DADU is
constructed with a parapet to have
no appearance of roof pitch.
Photo credit: Asmund & Jenny’s DADU, https://accessorydwellings.org
Photo credit: Constructive Form ADU, https://accessorydwellings.org
Visual Hierarchy
(left) the ADU uses colors consistent
with the primary structure but the
location, size, and window patterns
make it stand out from the main
house.
(right) The DADU is set back from
the main house and incorporates
the garage. It also uses consistent
materials and roof pitch to minimize
the visual impact of the DADU.
Photo credit: Rambo Halpern DADU, https://accessorydwellings.org Photo credit: Natalie Strom+Justin Strom DADU, https://accessorydwellings.org
Facade
Photos: (left) The DADU uses
material, color, and details to appear
signicantly consistent with the
primary home.
(right) The facades of the ADU and
the Primary home have no clear
relationship. The fenestration
patterns are dissimilar, the materials
are applied in a dissimilar way, and
the materials don’t appear to match
PHOTOS
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LAND USE STANDARDS
ADU
Design Standards for Detached ADUs
Detached ADUs are also required to meet the following standards.
• Main entrances must be at least 8 feet from side property lines
shared with a neighbor, if the entrance faces the neighboring
property.
• Second-story windows within 10 feet of the property line shall
be constructed to reduce direct views into the neighboring
property. Methods to do so include clerestory windows and
semi-translucent glass.
• The structure shall not intercept a 45-degree daylight plane
inclined into the site from a height of 15 feet above existing
grade from the 5-foot setback line.
Open Space
The overall site must maintain or provide at least 10% of the lot size as
usable and functional yard space (per TMC 13.06.100.D.7).
Walkways
For ADUs with a separate entrance, a walkway must connect to the
nearest public sidewalk or right-of-way.
• Walkways must be a minimum of 3 feet wide.
• Walkway materials must be distinct from any adjacent vehicular
areas (walkways may function as a shared drive/walk space along
an exterior edge of a driving surface).
Addressing
ADUs must have clear addressing visible from the street. If the ADU
is not visible from the street, an address and some form of directional
property line
property line
>8’-0”
>5’-0”
property line
property line
>8’-0”
>5’-0”
day
li
g
ht
pl
an
e
5’-0”
setback
15’-0”
DADU
property line
45º
The structure shall not intercept a 45-degree daylight plane inclined into the ADU site from a height of 15 feet above existing grade, measured from the required 5-foot setback line.
property line
10’-0”
semi-translucent
Neighboring
property
GARAGE
DADU
translucent
clerestory windows
10’ feet from the property line
Second story windows facing abutting residential properties and within 10 feet of the property line shall be constructed in a manner that reduces direct views into the neighboring property
through such methods as clerestory windows or semi-translucent glass
If the main entrance does
not face the property line
it is subject to standard
setback requirments
Daylight Plane Diagram
Entry Door Diagrams
Window Diagram
If the main entrance is
facing the property line it
must be located at least
8’-0” from the nearest
property line
A D U D E S I G N G U I D E - 12
notation must be along a walkway, on a fence, on the main house, or some location that dierentiates the
main house address from the ADU address and is visible from the main access point to the property.
Detached ADUs and other Accessory Structures
Detached ADUs are considered accessory structures (per TMC 13.06.100.F). Other kinds of accessory
structures include garages and sheds. There are several dierences in standards for Detached ADUs and
other accessory structures:
• Detached ADU size is calculated dierently than other types of accessory structures (see ADU Size).
• Only Detached ADUs are permitted to contain habitable space. Plumbing is not permitted in an
accessory building without a nding by the Building Ocial that such plumbing will not permit
the accessory building to be utilized as habitable space.
• For sites with more than one accessory structure, if one of them is a Detached ADU, an additional
500 square feet may be added to the total square footage of accessory structure footprints. This does
not increase the permitted size of the ADU. The following accessory structures standards apply to
Detached ADUs:
• Detached accessory buildings located on corner lots shall provide the main building side yard
setback along the corner side property line.
• Detached accessory buildings shall be located on the same lot or parcel on which the main building
is situated.
• For through lots, if there is an established pattern of “functional front and rear yards,” detached
accessory buildings shall be allowed in the “functional rear yard.”
• For garages that include vehicular doors facing the front property line, the building or portion of
the building with such doors shall be setback at least 20 feet from the front property line or private
road easement.
• Commercial shipping and/or storage containers shall not be a permitted type of accessory building in
any residential zoning district.
Home Occupations
Home occupations (businesses) are allowed, subject to regulations. If both the main dwelling and the ADU
contain home occupations, only one of the two is permitted to receive customers on the premises.
Rentals
One or both of the dwellings may be rentals, subject to the rental code and licensing requirements. If one of
the dwellings is used as a short-term rental, the property owner is required to occupy the other dwelling.
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ADU
DEVELOPMENT STANDARDS
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Building and Utility Standards
This section addresses common building and utility standards for dierent types of ADUs. Land use and
design considerations are summarized in Section 2. There are dierences for Attached versus Detached
ADUs, and for new construction versus conversion/addition to existing structures. For further information,
contact PDS at (253) 591-5030 or visit www.tacomapermits.org.
Construction Requirements for All ADUs
General: Accessory dwelling units must comply with construction codes including, but not limited to:
International Residential Code (IRC) with City and State adopted amendments, Washington State Energy
Code (WSEC), Uniform Plumbing Code (UPC), and City of Tacoma Minimum Housing and Structures Code,
Tacoma Municipal Code (TMC) 2.01, and other applicable codes
Design Loads: All structures must show compliance with the IRC. The vertical and lateral loads must
show compliance with prescriptive IRC requirements with loads transferring from the roof through the
foundation. If the work does not meet prescriptive IRC requirements, then design by an engineer licensed
in the State of Washington meeting International Building Code requirements is necessary.
Fire Separation Design: The location of an ADU must comply with separation distance requirements per
the IRC R302. The distance between two detached structures must be identied. If the distance between
the dwelling unit walls and eaves is less than 10 feet, then re-rated design is required per IRC Table
R302.1(1) or R302.1(2). These Tables also addresses opening limitations and eave projections. In addition, if
any part of the structure is within 5 feet of the adjacent property line, then re rating must be addressed
per the Tables. Attached ADUs are to be constructed to duplex standards with re separation between the
units and at supporting walls consistent with IRC R302.3.
Living Space: Units must have a kitchen with a sink, cooking facilities, and food preparation area. Units
must have permanent heating, hot water, and habitable rooms meeting a minimum 7 feet width with 70
square feet area. The ceiling height must be 7 feet minimum. Bathroom facilities are required with sink,
toilet, and shower or bathtub. Plumbing xtures shall have clearances per IRC R307. Ventilation exhaust
fans at bathrooms, kitchen, laundry, and whole house must be identied per IRC section M1507 and
associated State Amendments.
Safety: The work must meet IRC Chapter 3 for safety, including, but not limited to:
• The studio living space or bedroom area shall not directly access from the garage area per IRC
R302.5.1.
• Windows within 2 feet of doors and at bathrooms must provide safety glazing per IRC R308.
• Bedrooms and sleeping areas shall have emergency escape openings meeting IRC R310: 5.7
square feet with minimum width of 20” and minimum height of 24”.
• The entry door must be 32” wide with the door in the open position and clear height not less than
78”. There shall be a landing on each side of the door that is the width of the door and minimum
36” in direction of travel per IRC R311.
• Fall protection is required per IRC R312 if a window is less than 24” above the oor and over 72”
above exterior adjacent grade.
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BUILDING/UTILITY STANDARDS
ADU
A D U D E S I G N G U I D E - 14
• Smoke and carbon monoxide detectors shall be interconnected with battery back-up per IRC and
State Amendments sections R314 and R315.
Energy: The unit must fully comply with WSEC requirements. Insulation, glazing U-value, and door
requirements must be consistent with WSEC Table R402.1.1 and must be clearly identied on the plans
and glazing shedule. The new dwelling area must comply with the additional energy credit requiremets of
WSEC section R406.2, Link: WSEC Energy Credits . If ecient xtures are proposed for compliance with the
energy credits, then they must be identied on the oor plans and, if they will be exterior to the structure,
on site plans. A minimum of 75% of lamps in permanently installed lighting xtures shall be high-ecacy
lamps. Please note per WSEC R403.7.1 that electric resistance zone heated units in dwellings and using
electric zonal heating (baseboard, Cadet, etc.) as the primary heat source shall install an inverter-driven
ductless mini-split heat pump in the largest zone in the dwelling. Building permit drawings shall specify
the heating equipment type and location of the heating system. The exception to this requirement is if you
can show the total installed heating capacity of 2 kW per dwelling unit or less.
Manufactured Homes must meet vertical and lateral loads including seismic, snow, and wind that are
evaluated by an engineer licensed in the State of Washington. Manufactured structures must meet Tacoma
Municipal Code 2.02.620 and be new, double wide with sections 12 feet wide by 36 feet long, have
minimum 3/12 roof pitch, have siding materials commonly used on conventional site-built single family
residences, have skirting under the structures or concrete foundations, and meet WSEC.
Modular Homes must meet IRC requirements with City and State Amendments at time of submittal. See
related tip sheet for clarity on the dierences of manufactured and modular buildings.
Fire Sprinkler system may be necessary for any dwelling with points on exterior walls more than 150 feet
from the nearest re apparatus access road. In addition, re sprinkler systems for any dwelling with points
on exterior walls more than 600 feet from the nearest re hydrant.
A roadway less than 20’ wide and alleys are not considered access roads.
Specic Requirements for Converting Existing Space/Building to ADU
General: The space being converted must be evaluated for existing legal heated habitable space.
If the space was not existing legal heated living space, then the area must come into full compliance
with active codes at the time of submittal for previously identied Design, Fire Separation, Living
Space, Safety, Energy, and any other requirements for new living space at an existing building.
If the space was existing legal heated living space, then any modications to the space must come
into compliance with active codes at time of submittal.
Common considerations: Plans for conversions must address these common issues, if applicable:
• Plans must address the increase of live loads from storage to habitable space.
• Garages being converted to living space require that the vehicle openings be properly inlled
and addressing earth-wood separation per IRC R317. The separation usually consists of constructing
a reinforced concrete curb with anchor bolts meeting IRC foundation and wall requirements or by
removing exterior grade to provide separation and proper sloping to prevent moisture from
collecting at the foundation. The garage vehicle door needs to be removed and replaced
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with weather resistant siding of consistent materials to primary structure, insulation,
breathable moisture barriers, and interior nishes.
• Opening in-ll above the foundation stem wall requires siding material, breathable moisture barrier,
sheathing, insulation and interior nish all meeting IRC requirements.
• For basements being converted to ADU living space, applicants should review the Basement Tip
Sheet and address exterior wall drainage and wall exterior waterproong per IRC R405 and
IRC R406. As an alternative, the drawings can mitigate moisture by showing roof drainage
being collected and directed down to vegetated yard space or other approved location that
is identied on a site plan, grades adjacent to foundations shall be sloped away at
6” vertically at 10’, and there shall be no evidence of past moisture issues including
sump pumps, interior drainage, or wall/oor staining. The submittal must provide
wall section details that indicate exterior moisture protection system or provide details and site plan
with discharge locations per the alternative method described.
Specic Standards for Attached ADUs
Attached ADUs should be constructed to duplex standards with re separation between the units and at
the supporting structure per IRC R302.3.
An applicant may consider an alternative to duplex construction standards if documentation is provided
that meets all 3 criteria below per Washington State Amendments to the IRC:
1) The accessory dwelling unit is constructed within an existing dwelling unit. This requires the
unit to have connection with enclosed spaces and provide the appearance as one common
house.
2) Either the accessory dwelling unit or primary dwelling unit is owner-occupied. This will
require recording on title of an owner occupancy agreement to assure proper use now and
with potential future ownership.
3) All required smoke alarms in the accessory dwelling unit and the primary dwelling unit
are interconnected in such a manner that the actuation of one alarm will activate all alarms
in both the primary dwelling unit and the accessory dwelling unit.
If an existing ADU is modied to not be owner occupied, then permits are required to modify and/or verify
construction meets duplex standards referenced previously.
Legalization of nonconforming ADUs
Nonconforming ADUs existing prior to the enactment of these requirements may be found to be
legal if the property owner applies for an ADU building permit prior to December 31, 2020, and
brings the unit up to Minimum Housing Code standards set forth in Section 2.01 of the Building
Code. In addition, all nonconforming ADUs must meet all of the standards within Subsection C
Requirements, as well as Subsection D.4 Location. After January 1, 2021, owners of illegal ADUs shall
be subject to the enforcement provisions of TMC 13.05.100. The burden of proof falls on property
owners in any dispute regarding the legality of the unit.
Minimum Housing Code TMC 2.01.030 section A requires additions or alterations to be consistent to
the Building Codes. The applicant must provide documentation outlining the conversion to the ADU
with scope of work, oor plans, framing plans, section views, details, possibly engineering, and other
A D U D E S I G N G U I D E - 16
clarifying documents that shows the work meets code requirements when permitted. If unpermitted,
then it will be evaluated on an individual basis based on historic information available, information
presented by the applicant, and drawings submitted. Any work identied that requires a permit shall
be obtained and inspected to current code requirements.
Subdividing property with a Detached ADU
A detached ADU may remain on a lot or parcel where no main building exists: (1) in the event the
main structure on a lot is damaged or for other reason, is required to be removed; or (2) if the
property is subdivided in such a manner that the detached ADU would be located on a separate
building site. In either case, a building permit for construction of a main structure shall be required
to be obtained within one year of removal or division of property and substantial construction
completed in accordance with the plans for which the permit was authorized.
If a property with an existing single family dwelling and an ADU is subdivided with a result that the
ADU is on a separate property, then the ADU must either be converted to single family dwelling per
Land Use and Site Improvement standards and subject to separate utility services and may include
frontage improvements for the change of use, or permits for construction of a new single-family
dwelling on the ADU site must be submitted.
Utilities for ADUs
General: Utility lines and impervious surface areas must be identied on a separate utility plan. For more
info, visit www.tacomapublicutilities.com.
Site Development considers detached and attached ADUs to be accessory structures and right-of-way
improvements are only necessary to address impacts created by the development. Requirements may
include restoration for new or upgraded utilities, modications to driveway or curb access if proposed, or
associated construction damage. Future conversions or change of use to a primary residence will trigger
street frontage improvements through Tacoma Municipal Code (TMC) 2.19.
Sanitary Sewer services may be connected to existing primary dwelling sewer if adequate load and
design is available. A side sewer permit is necessary for impacts and/or modications to the exterior sewer
lines of the structures. Sanitary sewer service must comply with the City of Tacoma Side Sewer Manual.
Sewer line may be connected to existing on-site lines if existing lines are adequate. Sewer service must
have 10 foot horizontal separation from water service and be 18” lower than water service. If minimum
separation distances cannot be met then they shall be designed in accordance with the Department of
Ecology’s Criteria for Sewage Works design, Section C1-9. Storm water and Sanitary Sewer 253-591-5760
http://tacomapermits.org/sanitary-sewer-stormwater-library
Surface Water must be addressed for impervious surfaces if over 2,000 square feet since January 1, 2003
per the Stormwater Management Manual. Also, drainage shall not discharge to adjacent properties.
Stormwater and impervious surfaces shall be addressed per Storm Water Design Manual. New impervious
surfaces and structure area exceeding 2,000 square feet since January 1, 2003 must be addressed through
Storm Water Site Plan (SSP form) and Stormwater Pollution Prevention Plans (SWPPP).
Electrical service requirements are provided through Tacoma Power. They can be reached at (253) 502-
8436. It is highly recommended to contact Tacoma Power during the design process to understand
potential conicts of service that may require pole or service relocations. Please note that new ADUs
will be required to have a separate meter installed. No sub paneling will be allowed. Water service
metering requirements are provided Tacoma Water. They can be reached at (253) 502-8247. It is highly
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recommended to contact Tacoma Water to understand potential water meter service requirements and
additional dwelling service fees. Meter sizing may be impacted by requirements for re sprinkler systems
and distances. During the submittal, provide existing water service line sizing and proposed line sizing to
the new structure to verify adequate service. See separation requirements detailed in the Sanitary Sewer
section previously identied. Tacoma Power (253) 502-8436 https://www.mytpu.org/building-remodeling/
permits/electrical-permitting/
Garbage/Recycling Solid Waste: Contact Solid Waste at 253-502-2100 for solid waste service
requirements. Solid waste service is required for all occupied residences in the City of Tacoma and must
comply with provisions as stated in TMC 12.09. Solid Waste Management reserves the right to establish
the appropriate level of service. Properties that increase dwelling unit counts to three or more living units
are subject to applicable rate category and billing class changes. Solid Waste https://www.cityoftacoma.
org/cms/One.aspx?portalId=169&pageId=60729
Other Services: Utilities including natural gas and cable television should be coordinated with those
independent service providers separately. Gas service modications require separate review and
permitting. Tacoma Water 253-502-8247 https://www.mytpu.org/building-remodeling/permits/ 253-502-
8247.
Ballard ADU in Seattle, WA. Photo Credit: Cast Architecture.
Page 1 of 2
***AA
This checklist may be used as a guide for basic requirements to prepare an application. Submittal of additional plans or
information may be required to complete a building review, and/or review for shoreline or historic properties, critical areas, and
those that require geotechnical analysis due to steep slopes or unstable soils. If you’d like to find out whether these items
could apply, please contact us at (253) 591-5030. Also see Drawings: Site Plans, Floor Plans, and Elevations
.
Property Information
Site Address:
Parcel No.:
Estimated Value:
$
Provided
Submittal Requirements
NOTE: All drawings must be in one PDF file named “Drawings”. Your “Drawings” PDF is a required
attachment to your building permit application. Drawings must include sheets for Site Plan, Utility Plan, Floor
Plans, Framing Plans, Roof Plans, Elevations, Section Plans, and Foundation Details as described below.
REQUIRED QUESTIONS:
Type of ADU: Attached ADU Conversion, Detached ADU Conversion, ADU Addition to House
ADU Size:__________sq ft , Main Dwelling Size(w/o ADU) __________sq ft , ADU Height: _____ft
Owner Occupy? Yes / No , Existing Parking stall #_______ Removed Parking #______
Renting?:
House /
ADU /
Both , Rental Price House$__________ADU $__________
Site Plan that shows the following:
North arrow with property lines and corners and dimensions of parcel,
Building footprints with dimensions and setback from property lines and other buildings on the property,
Legend describing details and/or plan symbols and identify adjacent streets and alleys,
Open space detailed with calculations. (TMC 13.06.100.D.7 Minimum Usable Yard Space)
Foot print square footage of house and ADU
Driveways and parking areas with dimensions, existing/proposed gravel or paving area
Address signage location identified that is visible from the street for house and ADU.
Floor plans drawn to scale for all levels of the house and ADU with the following:
Dimensions and use of each room (existing and proposed)
Plumbing fixture location (basement fixtures may need backwater valves)
Ventilation for the new dwelling unit being created including whole house, bathroom, laundry, kitchen, etc.
Location of smoke and carbon monoxide detectors
Location of all windows and doors with dimensions and shear wall/brace wall locations.
For garages being converted to living space, provide section view showing garage vehicle door infill
Framing plans for floors, roof, walls which specify size & spacing of framing, beams, headers, etc.
Either provide engineering calculations addressing vertical and lateral loads, or show compliance with
prescriptive requirements of the adopted International Residential Code.
Roof plans – peaks, valleys, overhangs with dimensions, if modifications to roof proposed.
Elevations drawings including the following:
Labeled "looking north", " looking south", " looking east", and " looking west"
Height of the structures with roof pitch of house and ADU
Specify trim and siding materials on house and ADU
Location of all windows and doors with dimensions for house and ADU
Section plans and connection details including the following:
Detail compliance with energy code insulation
Identify load path from roof to foundation.
Identify ceiling heights of each level, especially at basements and bathroom fixtures with sloped ceilings
Foundation details that show live and dead loads are adequately supported with footings, reinforcement,
anchorage, and materials.
All items listed above must be combined into one PDF attachment. PDF file name: Drawings
Planning and Development Services
Submittal Checklist for:
Attached/Detached ADU Conversion or ADU Addition to House
Page 2 of 2
Utility plan that shows the following:
Property lines and corners with dimensions of parcel and adjacent streets and alleys,
Sewer line existing and proposed with distances from property lines and structures on the property,
Water lines existing and proposed with distances from property lines and structures on the property,
Electrical service lines existing and proposed with distances to structures on the property,
Garbage can locations on the property,
Storm Water evaluation requires calculations for all impervious surfaces since January 1, 2003. This includes
new structure footprint, concrete pathways, driveways being installed, and other impervious surfaces.
Other utility locations. Like gas service, if applicable.
Energy meeting Washington State Energy Code requirements including:
Additional energy credits,
Insulation at walls, ceiling, floor, slab and slab edges,
Glazing U-values.
Electric resistance heating will require inverter-driven ductless mini-split system heatpump in the largest zone
of ADU. This is not required if it can be shown the heating capacity of 2kW or less for the ADU.
Additional energy code information is available online here: Energy
PDF file name: Energy Code Forms
Stormwater Site Plan (SSP), if more than 2,000 sq ft of new impervious surfaces since January 1, 2003 or
grading more than 50 cubic yards. PDF file name: SSP
Stormwater Pollution Prevention Plan (SWPPP), if more than 2,000 sq ft of new impervious surfaces since
January 1, 2003 or grading more than 50 cubic yards. PDF file name same: SWPPP
Fire Separation details.
One hour fire rated separation between the two attached dwelling units.
One hour fire rated walls required at supporting structure, unless automatic fire sprinkler system installed.
Listed fire rated assembly and opening limitations are required for structures within 10 feet.
Listed fire rated assembly and opening limitations are required within 5 feet of property line.
If approved owner occupy agreement is completed and interconnected smoke and carbon monoxide
detectors are installed, then an attached ADU will not require fire separation between the units or supporting
structure.
Other common items include:
For amnesty of existing ADU per TMC 13.06.___, provide: past permits, supporting historical evidence, and
plans note for permit determination. This should be submitted as a detached/attached conversion.
Reports identified by staff which may include geotechnical report, height survey, wetland report, historical
approval, variance, or other decision or determination.
Provide itemized materials list and labor costs for verification of estimated values
Notes
You may apply for an Attached ADU Conversion, Detached ADU Conversion, or ADU Addition to Existing House
as a Residential Building Alteration Permit online at https://aca.accela.com/tacoma/
.
Instructions: Once you’ve registered online, login and select Permits to submit an application for Residential Alteration. All submittal
requirements must be attached to your application as PDF’s labeled as noted above, flattened and unprotected, except that
stormwater modeling files may be submitted in their native formats (e.g. .whm, .wh2, .mgs).
If you need assistance or are unable to submit online, please contact us at (253) 591-5030.
For electrical and water meter permits, contact Tacoma Public Utilities (TPU) www.mytpu.org.
Note: This checklist does not substitute for codes and regulations.
The applicant is responsible for compliance with all codes and regulations, whether or not described in this document.
More information: City of Tacoma, Planning and Development Services | www.tacomapermits.org (253) 591-5030
To request this information in an alternative format or a reasonable accommodation, please call 253-591-5030 (voice).
TTY or STS users please dial 711 to connect to Washington Relay Services.
Page 1 of 2
***AA
This checklist may be used as a guide for basic requirements to prepare an application. Submittal of additional plans or
information may be required to complete a building review, and/or review for shoreline or historic properties, critical areas, and
those that require geotechnical analysis due to steep slopes or unstable soils. If you’d like to find out whether these items
could apply, please contact us at (253) 591-5030. Also see Drawings: Site Plans, Floor Plans, and Elevations
.
Property Information
Site Address:
Parcel No.:
Estimated Value:
$
Provided
Submittal Requirements
NOTE: All drawings must be in one PDF file named “Drawings”. Your “Drawings” PDF is a required
attachment to your building permit application. Drawings must include sheets for Site Plan, Utility Plan, Floor
Plans, Framing Plans, Roof Plans, Elevations, Section Plans, and Foundation Details as described below.
REQUIRED QUESTIONS: Type of ADU: New Detached ADU Building,
New SFD with Attached ADU
ADU Size:__________sq ft , Main Dwelling Size(w/o ADU) __________sq ft , ADU Height: _____ft
Owner Occupy? Yes / No , Existing Parking stall #_______ Removed Parking #______
Renting?: House / ADU / Both , Rental Price House$__________ADU $__________
Site Plan that shows the following:
North arrow with property lines and corners and dimensions of parcel,
Building footprints with dimensions and setback from property lines and other buildings on the property,
Legend describing details and/or plan symbols and identify adjacent streets and alleys,
Open space detailed with calculations. (TMC 13.06.100.D.7 Minimum Usable Yard Space)
Foot print square footage of house and ADU
Driveways and parking areas with dimensions, existing/proposed gravel or paving area
Address signage location identified that is visible from the street for house and ADU.
Floor plans drawn to scale for all levels of the house and ADU with the following:
Dimensions and use of each room (existing and proposed)
Plumbing fixture location (basement fixtures may need backwater valves)
Kitchen location and exhaust fan venting outside for new ADU
Whole house ventilation for the new dwelling unit being created
Location of smoke and carbon monoxide detectors
Location of all windows and doors with dimensions and shear wall/brace wall locations.
Framing plans for floors, roof, walls which specify size & spacing of framing, beams, headers, etc.
Either provide engineering calculations addressing vertical and lateral loads, or show compliance with
prescriptive requirements of the adopted International Residential Code.
Roof plans – peaks, valleys, overhangs with dimensions, if modifications to roof proposed.
Elevations drawings including the following:
Labeled "looking north", " looking south", " looking east", and " looking west"
Height of the structure
Roof pitch of house and ADU
Specify trim and siding materials on house and ADU
Location of all windows and doors with dimensions for house and ADU
Section plans and connection details including the following:
Detail compliance with energy code insulation
Identify ceiling heights of each level, especially at basements and bathroom fixtures with sloped ceilings
Foundation details that show live and dead loads are adequately supported with footing dimensions, depth,
reinforcement, anchorage, and materials.
All items listed above must be combined into one PDF attachment. PDF file name: Drawings
Planning and Development Services
Submittal Checklist for:
New Building with Detached ADU or New SFD with Attached ADU
Page 2 of 2
Utility plan that shows the following:
Property lines and corners with dimensions of parcel and adjacent streets and alleys,
Sewer line existing and proposed with distances from property lines and structures on the property,
Water lines existing and proposed with distances from property lines and structures on the property,
Electrical service lines existing and proposed with distances to structures on the property,
Garbage can locations on the property,
Storm Water evaluation requires calculations for all impervious surfaces since January 1, 2003. This
includes new structure footprint, concrete pathways, driveways being installed, and other impervious
surfaces.
Other utility locations. Like gas service, if applicable.
Energy meeting Washington State Energy Code requirements including:
Additional energy credits,
Insulation at walls, ceiling, floor, slab and slab edges,
Glazing U-values.
Electric resistance heating will require inverter-driven ductless mini-split system heatpump in the largest
zone of ADU. This is not required if it can be shown the heating capacity of 2kW or less for the ADU.
Additional energy code information is available online here: Energy
PDF file name: Energy Code Forms
Stormwater Site Plan (SSP), if more than 2,000 sq ft of new impervious surfaces since January 1, 2003 or
grading more than 50 cubic yards..PDF file name: SSP
Stormwater Pollution Prevention Plan (SWPPP), if more than 2,000 sq ft of new impervious surfaces since
January 1, 2003 or grading more than 50 cubic yards.
PDF file name same: SWPPP
Other items identified by staff, which may include geotechnical report, height survey, wetland report,
historical approval, variance, or other decision or determination.
Notes
You may apply for an ADU New Residential Building Permit (BLDRN) online at https://aca.accela.com/tacoma/.
Instructions: Once you’ve registered online, login and select Permits to submit an application for Residential New Building. All
submittal requirements must be attached to your application as PDF’s labeled as noted above, flattened and unprotected, except
that stormwater modeling files may be submitted in their native formats (e.g. .whm, .wh2, .mgs).
If you need assistance or are unable to submit online, please contact us at (253) 591-5030.
For electrical permits, contact Tacoma Public Utilities (TPU) www.mytpu.org.
Note: This checklist does not substitute for codes and regulations.
The applicant is responsible for compliance with all codes and regulations, whether or not described in this document.
More information: City of Tacoma, Planning and Development Services | www.tacomapermits.org (253) 591-5030
To request this information in an alternative format or a reasonable accommodation, please call 253-591-5030 (voice).
TTY or STS users please dial 711 to connect to Washington Relay Services.
