Everything homeowners need to know about building an accessory dwelling unit in Tacoma - size limits, setbacks, permits, and how the city's own standards layer on top of Washington's statewide ADU law.
Last verified: August 2026
8/10 · ADU-friendly
1,000 sq ft
Max ADU size
18 ft*
Max height
Not required
Owner-occupancy
By-right
Permit type
This page summarizes Tacoma Municipal Code 13.06.150 (Accessory Dwelling Units), as amended by Council Substitute Ordinance No. 28858, and Washington's statewide ADU law (HB 1337, 2023) for general reference - it is not legal advice. Always confirm current requirements with Tacoma Planning and Development Services (PDS) before designing or applying for permits. See sources below.
Zoning & size requirements
What you're allowed to build
ADU type
Max size
Max height
Notes
Detached (DADU)
1,000 sq ft of living area, excluding non-living areas
18 ft under the city's published local standard, no taller than the main house
Must sit in the rear yard behind the primary structure; a DADU built within an existing garage footprint is exempt from setback rules
Attached (AADU, addition, above-garage, basement)
Sized within the primary structure - no separate detached-style footprint cap
Matches the primary structure's standard zone height limit
Common approach for a basement or above-garage conversion
Allowed zoning districts
ADUs are allowed citywide as an accessory use to a primary residential structure, most commonly on R-1 and R-2 single-family lots as well as multifamily zones. Note: Tacoma's published height figure of 18 ft (up to 20 ft with a parking or green-building bonus) predates a 2023 statewide requirement that Washington cities allow ADU heights up to at least 24 ft where the primary home is that tall - confirm the currently applicable limit for your zone with PDS.
Additional standards
Setbacks, parking & other rules
Setbacks
5 ft from side property lines (8 ft if the ADU entrance faces the side line); rear setback was reduced to 10 ft in a February 2025 code update; no setback required from an alley
Parking
Not required for ADUs anywhere in the city
Units per lot
Up to 2 ADUs allowed as an accessory use to a primary residential structure, any combination of attached and detached
Owner-occupancy
Not required. Washington's 2023 statewide law (HB 1337) permanently bars cities from requiring it
Building code
Must meet Washington State Residential Code dwelling-unit standards
Impact fees
Capped at no more than 50% of what's charged for the primary dwelling unit, per HB 1337
Ordinance history
How Tacoma's ADU rules got here
2019Local ADU rules updated. Tacoma amended its ADU standards (Amended Ordinance No. 28576, March 2019), building on a code that was already relatively permissive by national standards, with average permitting still under 7 ADUs per year at the time.
2023Washington passes HB 1337. The statewide law requires cities to allow 2 ADUs per lot in urban growth areas, guarantees at least 1,000 sq ft of ADU floor area, caps ADU impact fees at 50% of the primary unit's fee, and bars parking mandates near transit.
2023 (Nov)Local code brought into compliance. Council Substitute Ordinance No. 28858 amended TMC 13.06.150 to allow 2 ADUs per single-family lot, eliminated parking requirements within a half-mile of Tacoma Link light rail stations, and exempted DADUs built within an existing garage footprint from standard setback rules.
2025 (Feb)Setback standards eased further. The city reduced the required DADU rear setback to 10 ft.
2025 (Jul)Permitting milestone. City data reported 581 ADUs permitted since the policy changes took effect, with the pace rising from an average of fewer than 7 per year before 2019 to roughly 10 per month afterward.
Tacoma is Washington's second-largest city and has leaned into what local officials describe as "gentle density" - adding housing capacity through ADUs rather than larger multifamily buildings. The permitting data backs up the strategy: activity has grown roughly fifteenfold from the pre-2019 baseline.
Permit process
How Tacoma ADU permitting works
1
Pre-application check
Confirm your zone and lot eligibility with PDS, 747 Market Street, 3rd Floor, (253) 591-5030, before designing.
2
Choose a pre-approved plan or custom design
Tacoma's pre-approved DADU program offers four base models with plan preparation included at no charge, which can speed up permitting compared to a fully custom design.
3
Prepare your plan set
Submit electronic PDF plans meeting current code requirements, including a site plan and, for attached units, floor plans of the existing home.
4
Submit for permit review
Apply online at TacomaPermits.org or in person with PDS. Depending on scope, expect building, plumbing, mechanical, site development, side sewer, stormwater, water, and/or electrical permits.
5
Utility coordination
Coordinate water service and sanitary sewer rate changes with Tacoma Public Utilities as part of the application.
6
Construction & inspections
Once permits issue, build and schedule inspections, then request your final address before occupancy.
Fees and review timelines vary by project scope and current volume - confirm current figures with PDS.
Budgeting
What it costs to build an ADU in Tacoma
Garage conversion
Roughly $65,000-$170,000, the least expensive path since the shell already exists
New detached ADU (DADU)
Roughly $140,000-$310,000+ for a code-compliant, freestanding unit
Pre-approved plan savings
Plan preparation is included at no charge under the city's pre-approved DADU program, which can reduce design cost and review time compared to a custom plan
Utility fees
Water service and sanitary sewer rate changes for the added unit are billed separately from permit fees and vary by project
These are general ranges from local contractor estimates and regional reporting, not quotes - actual cost depends heavily on site access, utility connections, and finishes.
Before you apply
Tips for a smooth approval
Check whether a pre-approved DADU plan fits your lot. Four base models are available with plan preparation included at no charge.
Plan for two ADUs if you might want them. Since Tacoma allows up to two per lot, decide early whether you want one attached and one detached, or two detached units, so your site plan doesn't box you in.
Budget separately for utility connection costs. Water and sewer fees for the added unit are billed apart from your building permit fees.
Confirm the current setback and height standards before finalizing your design. Tacoma has updated these rules more than once in recent years, most recently easing the rear setback in February 2025, so older guidance you find online may be out of date.
Ask about the garage-footprint exemption. Converting or rebuilding within an existing garage footprint can exempt a DADU from standard setback rules.
FAQ
Common questions
Do I need to live on the property to build an ADU in Tacoma?
No. Washington's 2023 statewide law (HB 1337) permanently bars cities from requiring owner-occupancy for ADUs.
How many ADUs can I build on one lot in Tacoma?
Up to two - any combination of one attached and one detached ADU, or two detached units, in addition to the primary residence.
Do I need extra parking for an ADU?
No. Parking is not required for ADUs anywhere in the city.
What's the maximum size for a detached ADU (DADU)?
1,000 sq ft of living area. Tacoma's published local height standard is 18 ft (up to 20 ft with a parking or green-building bonus), though confirm the currently applicable limit with PDS given the statewide height floor set by HB 1337.
How long does the permit process take?
Timelines vary by project scope and current review volume. A pre-approved DADU plan generally moves faster than a fully custom design - confirm current timelines with PDS.
How much does an ADU cost to build in Tacoma?
Garage conversions tend to run roughly $65,000-$170,000, and new detached units roughly $140,000-$310,000 or more, based on local contractor estimates and regional reporting - not counting utility connection fees.
How many ADUs has Tacoma actually permitted?
City data reported 581 ADUs permitted through July 2, 2025, since the city's post-2019 policy changes took effect - up from an average of fewer than 7 per year before 2019 to roughly 10 per month afterward.
What is Tacoma's pre-approved DADU program?
The city offers four pre-drafted detached ADU base models with plan preparation, site evaluation, and city support included at no charge. Because the plans already meet current building, residential, and energy codes, permitting and plan checks typically move faster than a custom design.
