Building an ADU or backyard cottage in Tacoma

What you can build in Tacoma

Tacoma's ADU rules are in Tacoma Municipal Code 13.06.080.A. "Two ADUs shall be allowed per residential lot" with any new or existing residential development. You can put an ADU inside or attached to the house, or in a detached building, often in the rear yard. ADUs are allowed on any legal lot, "irrespective of lot size or width," as long as the size, setback, amenity space and other standards are met.

Tacoma's Home in Tacoma zoning took effect February 1, 2025. It replaced single-family zoning with three Urban Residential zones: UR-1 and UR-2 (low scale) and UR-3 (mid scale). ADUs are allowed in any of the five housing types and all three UR zones. A detached ADU usually counts as a "Backyard Building," a housing type that can hold up to six units.

In UR zones, ADUs count toward the lot's density limit. Lots of record as of February 1, 2025, get at least four homes in UR-1, six in UR-2 and eight in UR-3, plus two more through the Bonus 1 program. Two attached ADUs added to an existing house make it a triplex under the building code. See our Washington ADU law page for the state rules behind these changes. [1][2][3][4]

Size, height and setbacks

Size. The habitable area of an ADU, "excluding any garage area and other non-living areas, shall be limited to a maximum of 1,000 square feet."

Height. ADUs have no height limit of their own; the zone and housing type set it. In UR-1 and UR-2 the limit is 35 feet, but only 25 feet in the rear 25 feet of the lot. UR-3 allows 35 feet. In View Sensitive Districts, a Backyard Building with one or two ADUs can be no taller than the main house.

Setbacks in UR zones:

• Front: 15 feet in UR-1 and UR-2, 10 feet in UR-3
• Rear: 15 feet in UR-1 and UR-2, 10 feet in UR-3; a Backyard Building needs no rear or side setback from an alley
• Side: 5 feet, or 8 feet on sides where a unit's main entrance faces the side yard

Buildings on the same lot must be at least 6 feet apart, or 10 feet when one is taller than 25 feet. A Backyard Building can be up to 40 feet wide in UR-1 and UR-2 and 40 feet deep. Keeping a tree at least 12 inches in diameter can shrink front and rear setbacks to 10 feet in UR-1 and UR-2 and raise the rear yard height limit to 35 feet.

Floor area and open space. UR-1 allows a floor area ratio of 0.6 for one or two units and 0.8 for three or more. Amenity space must be 10 percent of the lot in UR-1, 7.5 percent in UR-2 and 5 percent in UR-3. Check your zone on the city's Home in Tacoma page. [1][2]

Parking and walkways

"No off-street parking is required for ADUs." The code lets you remove existing off-street parking spaces to make room for an ADU. If you add parking, it must be in the rear part of the lot, and it can't be reached from the front if there is a developable alley. Bicycle parking rules in TMC 13.06.090.G still apply.

An ADU with its own outside entrance needs a walkway to the nearest public sidewalk, or to the street if there is no sidewalk. It must be made of materials that look different from the driveway or parking surface.

The city's ADU web page says adding an ADU "may not remove parking required for the primary dwelling." That is stricter than the code text, so confirm with Planning and Development Services if your plan removes a parking space. [1][2][4]

Fees

You pay building permit and plan review fees through the city's Accela permit portal. Use the city's fee estimator for a rough number.

Transportation impact fees. Starting June 1, 2026, Tacoma charges a one-time transportation impact fee on new development under TMC 10.31. The code has no ADU exemption, and the fee is due before the permit is issued. Washington law caps impact fees on an ADU at 50 percent of what the main house would pay. The city offers a TIF calculator on its transportation impact fee page.

Utility fees. Tacoma Power requires each new dwelling to be metered separately. The city's utilities guide for ADUs, based on rates in effect April 7, 2025, lists:

• Separate electric service: $970 to $1,797 (application, connection and inspection fees)
• Sharing the house's water meter: a $175.88 water system development charge
• A larger shared meter: $1,025.88 in water charges
• A separate water service and meter: $5,922.38 to $10,272.38, including flagging and paving charges that may apply

These charges may have changed since that date, so ask Tacoma Water and Tacoma Power for a current estimate. You must show the water system development charge was paid before you get a certificate of occupancy. For budgeting help, see our ADU cost guide. [2][5][6][7][8]

Pre-approved backyard ADU plans

Planning and Development Services offers four pre-approved detached ADU plans, designed to fit Home in Tacoma zoning:

• Unit A: 300 square foot studio
• Unit B: 520 square feet, one bedroom
• Unit C: 845 square feet, two bedrooms, over a 647 square foot garage
• Unit D: a duplex with two 534 square foot one-bedroom units

The city says the cost of the plans, site evaluation for services and city support "is included and initially free." Staff do a site visit with you and your contractor during pre-application. Changes beyond the plan options mean paying the designer, and big changes can take you out of the program.

A pre-approved plan "is not pre-permitted." You still need permits and site-specific review for utilities, critical areas, historic districts and fire access. See the plans on the city's ADU page. [2][9]

Garage and other conversions

Permitted or legally nonconforming accessory structures that existed as of February 1, 2025, in a UR or R district "may be converted to a dwelling unit regardless of conformance to setback, location, maximum height, or other development regulation." The building must meet current building code, and you must provide pedestrian access.

Construction permits are required for "creating, converting, or legalizing an ADU." The city has a separate submittal checklist for ADU conversions. See our garage conversion guide for the general steps. [1][2][4]

Owner incentives

Home in Tacoma gives extra flexibility to owner-occupants earning no more than 150 percent of the Pierce County family median income who add up to two ADUs. You must record a title restriction that one unit will be owner-occupied for at least the first five years after the certificate of occupancy. In return:

• The rear yard height limit in UR-1 and UR-2 rises to 35 feet
• No alley access is required if the alley isn't developed
• The on-site tree credit requirement drops to the minimum "floor" level, with no tree credit or canopy loss fees

This is optional. Washington law bars cities from requiring you to live on the property to build an ADU. [1][2][7]

Renting it out

You can use an ADU as a long-term or short-term rental. For a short-term rental of either the main house or the ADU, "the property owner is required to occupy one of the dwellings." If you rent individual guest rooms, an owner must live in that dwelling during the rental. Short-term rentals also need smoke and carbon monoxide detectors and a posted safety sign in each guest room.

Under Home in Tacoma, separate ownership of units is possible through a unit lot subdivision (TMC 13.04.093). Ask the city whether your lot qualifies. [1][2][4]

Permit steps in Tacoma

1. Check your zone

   Find your Urban Residential zone and any critical areas, historic district or view-sensitive overlay. The Home in Tacoma page links the zoning map and housing types. [2][3]

2. Get free residential coaching

   Submit a pre-application request in Tacoma Permits (ACA) with a site plan and your questions; ADUs qualify for free Residential Coaching, and the city responds within 2 business days. You can also call (253) 591-5030, option 3 then option 3. [2][10]

3. Pick a pre-approved plan or have plans drawn

   Choose one of the city's four pre-approved detached ADU plans, or prepare plans using the detached ADU submittal checklist or the conversion checklist. [2]

4. Plan utilities

   Decide on water and power service early using the utilities guide. Call Tacoma Power New Services at 253-502-8436 if power lines are near the ADU site, and Tacoma Water at 253-502-8247 for a fee estimate. [8]

5. Apply online

   Submit a residential new construction building permit in electronic PDF format on Tacoma Permits (ACA). Depending on scope you may also need plumbing, mechanical, site development, side sewer, stormwater, water or electrical permits. [2][9]

6. Pay fees and get your permit

   Pay plan review, permit and any transportation impact fees; impact fees are due before the permit is issued. Don't start work before the permit is issued, or you may face double fees. [4][5]

7. Build and pass inspections

   The city inspects for zoning and building, health, safety, energy and electrical code compliance. Show the water system development charge was paid before the certificate of occupancy. [1][8]

Pre-approved and sample plans

• Tacoma pre-approved detached ADU plans

  Four backyard ADU designs (300 sq ft studio, 520 sq ft one-bedroom, 845 sq ft two-bedroom over a garage, and a two-unit duplex), with plans and site evaluation initially free. [2][9]

Who to call

• Tacoma Planning and Development Services, Residential Development

  ADU zoning, permits, pre-approved plans and coaching (select option 3, then option 3)

  (253) 591-5030

  Tacoma Municipal Building, 747 Market Street, Third Floor, Tacoma, WA 98402

  [2]

• Tacoma Water Construction & Development

  Water service, meters and system development charges

  253-502-8247

  [8]

• Tacoma Power New Services Engineering

  New electrical service and clearances from power lines

  253-502-8436

  [8]

• Public Works, Transportation Impact Fees

  Transportation impact fee questions and estimates

  (253) 325-8522

  [6]

Questions people ask