DADU vs. ADU in Tacoma, WA: How to Choose for Your Property
Choosing between a DADU and an attached ADU in Tacoma, WA, usually comes down to privacy, lot layout, and long-term financial goals. In most Pierce County neighborhoods, detached units offer stronger rental income and privacy, while attached ADUs can be easier to permit and cheaper to build per square foot, especially on constrained or septic lots.
What Is the Difference Between a DADU and an ADU in Tacoma, WA?
In Tacoma's code, an Accessory Dwelling Unit is a secondary home on a residential lot. If it shares a wall, foundation, or roof with the main house, it is classified as an attached ADU. If it is a stand-alone structure in the yard, it is a Detached Accessory Dwelling Unit, or DADU.
Common attached ADU locations include:
A basement conversion under the existing home
A unit above an attached garage
A side-yard or rear addition that connects structurally
A DADU is usually a small cottage in the backyard, often oriented to a lane or alley where that exists in Tacoma, University Place, or Lakewood. In Pierce County, both attached and detached units are used for multigenerational housing, long-term rentals, or, where allowed, future condo-eligible units. Every lot is different, which is why Tacoma DADU always starts with site-specific feasibility before recommending a direction.
How Do Zoning, Lot Size, and Layout Affect Your Choice?
Zoning and lot layout often decide whether a DADU is even possible. Residential zones in Tacoma typically set limits for:
Maximum building height
Minimum setbacks from property lines
Total lot coverage or floor-area limits
According to the City of Tacoma Planning and Development Services, most single-family zones cap building height near 25, 35 feet and limit total lot coverage to roughly 35, 50% depending on zone (City of Tacoma, TMC 13.06). Detached units usually have stricter placement rules than additions that stay tied into the main house. A narrow or shallow lot might not fit a detached structure within rear and side setbacks, while an attached ADU could still tuck into unused space over a garage or at the back of the house.
Lot conditions also matter:
Steep slopes or retaining walls can make backyard construction complex
Large protected trees can shrink the buildable area
Utility easements can block where a DADU could sit
On septic, which is more common in some Pierce County pockets outside core Tacoma, an attached ADU can sometimes connect more simply to the existing system. A detached unit may require more engineering or even septic upgrades. The Washington State Department of Health notes that adding bedrooms can trigger septic evaluation and potential expansion (Washington DOH On-Site Sewage Systems). Tacoma DADU's process usually starts with a feasibility walk where the team measures, photographs, and maps these constraints before talking design.
Which Option Offers Better Rental Income, Privacy, and Value?
For rental income, detached units often have an advantage. Zillow rental data for Tacoma shows that small single-family homes typically rent for 10, 20% more than similarly sized apartments in the same neighborhood (Zillow Research, 2023). With their own yard space, dedicated entry, and no shared walls, DADUs in Tacoma can often justify higher rents compared to an in-house apartment of similar size. Many tenants will pay a premium for that privacy and acoustic separation.
Attached ADUs can still perform very well financially, especially when:
You can re-use existing foundation or roof lines
You avoid major site work or utility trenching
You design 1 to 2 bedrooms with efficient layouts
In practice, Tacoma owners commonly see attached ADUs in the 500, 800 square foot range and DADUs in the 600, 900 square foot range, creating strong rental income potential as long-term rentals. A 700-square-foot DADU renting at Tacoma's average of roughly $2.00, $2.50 per square foot can generate an estimated $1,400, $1,750 per month in gross rent, depending on neighborhood and finish level (Zillow Rent Index, 2023). That income can materially improve cash flow and long-term ROI, especially if the project is financed with a fixed-rate loan.
From a lifestyle angle, privacy is usually the biggest divider:
A DADU works well when you want clear boundaries, such as adult children, extended family, or tenants who need their own quiet space
An attached ADU is better when caregiving or frequent interaction is important, such as aging parents who need support but not a full roommate situation
For property value, appraisers in Pierce County typically look at income potential, square footage, and how well the unit is integrated. A 2019 Freddie Mac study found that properties with ADUs were appraised about 35% higher on average than similar homes without ADUs in certain West Coast markets (Freddie Mac, 2019). Detached units can feel like a second small house on the lot, which often makes their value more flexible over time. Attached ADUs can still add significant value by improving the function of the main home, for example, turning an unfinished basement into a legal dwelling that can later be used as living space, guest space, or rental.
What Does Washington State HB 1337 Mean for DADUs and ADUs in Tacoma?
HB 1337 is the state law that requires many cities, including Tacoma, to support more ADUs on residential lots. In simple terms, it allows up to two ADUs per qualifying lot, which can be:
Two attached units
Two DADUs
One attached ADU and one DADU
This opens the door for Tacoma and Pierce County owners to think beyond a single backyard cottage. It also introduces the possibility of condomizing a DADU so it can be legally separated and sold, which can change how some owners think about equity and long-term exit strategies. The Washington State Department of Commerce notes that HB 1337 also limits some off-street parking requirements and owner-occupancy rules to reduce barriers to ADUs (WA Dept. of Commerce, 2023).
The details matter a lot here. Local zoning, design standards, off-street parking rules, and utility capacity all shape what is actually realistic. HB 1337 covers both attached and detached forms, but you still have to respect height, setbacks, and lot coverage under the Tacoma Municipal Code and relevant Pierce County zoning updates. Working with a builder who is familiar with the law and local Pierce County code helps keep designs aligned with what the city will actually approve.
How Do Permitting, Construction, and Feasibility Work for Both?
For both DADUs and attached ADUs, Tacoma generally requires:
A complete site plan showing structures, setbacks, and topography
Architectural drawings that meet residential building code
Structural engineering when you add new framing or alter existing framing
Energy, mechanical, and plumbing documentation
Trigger points such as building height, proximity to property lines, or location near slopes can add extra reviews. A large two-story DADU near a rear property line, for example, might draw more scrutiny than a small attached unit tucked into an existing footprint.
Construction itself feels different on the ground:
A backyard DADU concentrates disruption in one part of the lot, but you may see more site access issues, material staging, and longer utility trenching
An attached ADU often affects daily life more, because crews are working in or on the existing house, with more interior noise, dust, and temporary loss of spaces like driveways or garages
Tacoma DADU's approach is to pair the feasibility study with a permit strategy, so you can understand not just whether a DADU in Tacoma, WA, fits, but how complex the review will likely be compared to an attached solution. That combination often determines whether a property owner chooses detached or attached for the first phase and how they might phase a second unit under HB 1337 in the future.
Conclusion: Choosing the Right ADU Path in Tacoma
Choosing between a DADU and an attached ADU in Tacoma, University Place, or greater Pierce County is ultimately a balance of privacy, zoning realities, septic and lot complexity, and long-term financial goals. Detached units often deliver stronger rental income and flexibility, while attached units can be more straightforward on tight or challenging lots.
Tacoma DADU draws on Matt Rody's combined background in construction, real estate, and finance to help homeowners in Pierce County weigh projected rental income, estimated property value increases, and overall ROI before committing to a design. By anchoring every project in feasibility, local code, including HB 1337 and current Pierce County zoning updates, and honest conversations about site constraints like septic and slopes, they aim to match each lot with the right detached or attached solution.
If you are considering a DADU or attached ADU on your Tacoma property and want clear guidance on what will fit, what it might rent for, and how it could impact your long-term equity, contact Tacoma DADU today to schedule a feasibility consultation.
FAQs: Common Questions About DADUs and ADUs in Tacoma
What Is the Difference Between a DADU and an ADU in Tacoma?
A DADU is a fully detached secondary home on the same lot as your main house. An attached ADU shares structure with the primary home, such as a basement apartment or addition. Tacoma's code treats them as the same family of use, but detached units usually face different setback and placement standards under the Tacoma Municipal Code.
Can I Build an ADU and DADU on My Tacoma Property?
HB 1337 and local updates now allow up to two ADUs per qualifying lot, which can include a mix of attached and detached units. Whether your specific Tacoma, University Place, or Lakewood property can handle both depends on zoning, lot size, and utility capacity. A site-specific feasibility review is needed to confirm how these state rules interact with current Pierce County zoning updates.
Which Is Cheaper to Build, a DADU or an ADU in Pierce County?
Attached ADUs are often less expensive per square foot because they can leverage existing structure and utilities, but all costs should be treated as estimates that depend on lot conditions and scope. DADUs require their own foundation, framing, and more site work, which can increase total project budgets. Factors like slope, tree removal, and septic upgrades can materially affect final costs for both options.
Does HB 1337 Apply to Both DADUs and ADUs in Tacoma?
Yes, HB 1337 applies to both attached and detached accessory dwelling units statewide. Cities such as Tacoma must align their codes with the law while still setting local standards for height, setbacks, and design. Owners should review both HB 1337 and Tacoma's latest zoning ordinances, along with Pierce County zoning updates if they are outside city limits.
Can I Rent Out Both an ADU and a DADU on One Property?
In many Pierce County areas, long-term rentals are allowed for both units if they meet code and local licensing rules. Short-term rental rules are often more restrictive and can vary by city and neighborhood. Checking current regulations and projected market rents is essential for estimating income, cash flow, and overall ROI.
How Does Lot Size Affect Whether I Can Build a DADU or ADU in Tacoma?
Smaller or irregular lots may struggle to fit a detached building within required setbacks, especially in the rear yard. An attached ADU can sometimes work on lots where a DADU would crowd property lines or exceed lot coverage. Professional measurements, a survey, and code checks are the only reliable way to know what each Tacoma or Pierce County lot can support.
Which Type Adds More Value to a Pierce County Property?
Both attached ADUs and DADUs can significantly increase value when they are legal, well-designed, and rentable. Detached units often feel like a separate small house, which many buyers value for flexibility and income potential, while attached ADUs can add value by turning underused space into legal, livable square footage. Appraisers typically weigh income potential, total finished area, and market demand when estimating the value impact of either option.
How Long Does It Take to Permit and Build a DADU vs. ADU in Tacoma?
Permitting and construction timelines vary with design complexity, review workload, and site challenges. Detached units with larger footprints or height can take longer to review and build than simpler attached conversions, especially if they trigger slope, tree, or utility reviews. The condition of the existing house, necessary utility upgrades, and septic or stormwater requirements all influence the overall schedule.
Can I Condo a DADU and Sell It Separately Under HB 1337?
State rules now open the door to condomizing a DADU so that it can be legally separated for sale, which can be appealing in high-demand Tacoma neighborhoods. Doing this involves legal work, lending considerations, and often HOA-style documents, and should be treated as a separate, complex project layered on top of the build itself. Owners should factor in attorney fees, potential reserve requirements, and long-term management obligations when evaluating this path.
How Do I Find Out Which Option Is Right for My Specific Tacoma Lot?
The only reliable way is a detailed feasibility assessment that looks at zoning, setbacks, utilities, septic capacity, and your financial goals. At Tacoma DADU, this assessment is paired with financial and design thinking, drawing on Matt Rody's construction, real estate, and finance background to help owners evaluate both attached and detached paths. Contact Tacoma DADU today to review your lot's constraints and opportunities and to clarify the likely rental income, value impact, and ROI for your project.
Get Started With Your Project Today
If you are ready to explore how a custom DADU can fit your property, we are here to guide you through every step. At Tacoma DADU, we start by understanding your goals, budget, and timeline so we can recommend the best path forward. Learn what is possible with a high quality DADU in Tacoma, WA and get clear, straightforward answers to your questions. Reach out today so we can help you move from ideas on paper to a finished space that works for your life.
