Can You Sell a DADU Separately in Washington?

This article explains how Washington law and Seattle's code treat the question. It is general information, not legal advice — separating a DADU from a house is a real estate transaction that needs a Washington attorney and, usually, a surveyor.

Short answer: in Washington you generally can sell a DADU on its own, but only through one mechanism — making the house and the cottage two units of a small condominium. You cannot split the lot and hand the backyard cottage its own piece of dirt. That distinction gets blurred constantly online, including by builders and developers who should know better, so it is worth being precise about.

What state law actually says

The operative sentence is in RCW 36.70A.681(1)(k), part of the 2023 statewide ADU law. A city or county:

“may not prohibit the sale or other conveyance of a condominium unit independently of a principal unit solely on the grounds that the condominium unit was originally built as an accessory dwelling unit.”

Read that carefully, because the wording does three specific things. It is an anti-discrimination clause, not a mandate — it does not create a right to sell an ADU, it stops a city from singling out ADUs for a ban. It applies to condominium units only, which means no lot splits and no unit lots. And it reaches jurisdictions planning under the Growth Management Act, inside urban growth areas — which covers Seattle and essentially every city we build in.

Seattle mirrored the language directly at SMC 23.42.022.K, adopted in Ordinance 127211, effective June 30, 2025 — the same ordinance that repealed owner-occupancy for ADUs. If you last looked into this a few years ago, that is the change. It is also worth knowing that SDCI's own public-facing ADU page still reads as though no separation is possible; the code language is what governs.

Why a lot split does not work

This is where most of the bad information lives. Two different subdivision tools exist in Seattle, and neither one will give a DADU its own lot.

Unit lot subdivision is explicitly closed to ADUs

A unit lot subdivision is the mechanism that lets townhouses and rowhouses each get fee-simple title on what was one parcel. SMC 23.24.045.G says a unit lot subdivision “shall not result in an accessory dwelling unit that is located on a different unit lot than the unit lot of the associated principal dwelling unit.” SMC 23.42.022.F carries the same same-lot requirement from the ADU side. The January 2026 Neighborhood Residential rewrite (Ordinance 127376) broadened unit lot subdivision to attached and detached units in all zones as part of middle housing — and left the ADU exclusion in place.

A fee-simple split needs a lot most people do not have

An ordinary subdivision or short plat is theoretically possible, but SMC 23.44.060.B sets a 5,000 square foot minimum lot size for lots created after January 21, 2026. Two conforming lots means a parent lot around 10,000 square feet before you account for access, and the existing house has to still meet its own setbacks and coverage on the smaller remnant. On a typical 5,000 square foot Seattle lot this is simply not available.

Washington did pass an administrative lot-split law — RCW 58.17.145, from E2SHB 1096 (2025 c 301). It is frequently miscited online under a different bill number. It also defers to local minimum lot size, and Seattle has until July 27, 2027 to implement it; as of late 2026 no implementing ordinance exists. So it is not a path you can plan a 2027 closing around.

How the condominium route actually works

A “two-unit condominium” sounds exotic and is not. It is a set of recorded documents that divide a single parcel into two separately ownable units plus common elements, governed by chapter 64.90 RCW, the Washington Uniform Common Interest Ownership Act. A great many web pages still cite chapter 64.34 — the old Condominium Act. For anything created now, 64.90 is the chapter that applies.

• A declaration (RCW 64.90.225) defining each unit's boundaries, the common elements, and each unit's allocated interests.
• A surveyor-certified map and plans recorded concurrently with the declaration (RCW 64.90.245). This is typically why a surveyor is involved.
• An owners association, organized before the first unit is conveyed (RCW 64.90.400), with governing documents and a mechanism for shared costs.
• Insurance on the common elements (RCW 64.90.470) and a reserve study unless the community qualifies for an exemption (RCW 64.90.545).

One genuinely useful feature: RCW 64.90.025(3) provides that chapter 58.17 RCW — the subdivision statute — does not apply to the creation of a condominium. You are not asking the City for subdivision approval. That is exactly why this route works where a lot split does not.

There is no “small community” shortcut for a condo

Chapter 64.90 has a limited-applicability provision for small communities (RCW 64.90.360(4)), and it is often described online as a light-touch on-ramp for two-unit projects. It covers plat communities and miscellaneous communities — not condominiums. A two-unit condominium gets the full chapter, including the public offering statement obligations at RCW 64.90.605 and the implied warranties of quality at RCW 64.90.670. Budget for a lawyer accordingly.

The 2025 warranty change almost nobody mentions

Implied statutory warranties are the reason many builders have historically refused to sell anything as a condominium. Washington addressed that specifically for ADUs. HB 1403 added RCW 64.90.675(4), which lets a declarant substitute an insured express warranty for the implied warranties where the unit is an accessory dwelling unit organized as a condominium:

• One year on workmanship and materials
• Two years on plumbing, electrical and ductwork systems
• Ten years on load-bearing structural elements

HB 2304, effective June 11, 2026, widened the companion category to projects of twelve or fewer units and four or fewer stories. The same legislation also added RCW 64.55.005(1)(c), exempting ADU condominium units from the building-enclosure design and inspection requirements of chapter 64.55 RCW — the envelope-peer-review regime that adds real cost to conventional condo construction.

Taken together, that is the reason a house-plus-DADU condominium is a practical product in 2026 in a way it was not in 2021. It is also the part of the picture that no other Seattle-area builder page we have found discusses.

Financing, taxes and recording

A buyer needs a lender who will finance a unit in a two-unit condominium. That is more workable than it sounds:

• Fannie Mae waives project eligibility review for two-to-four-unit condo projects (Selling Guide B4-2.1-02), and requires an ALTA 4 or 4.1 title endorsement.
• Freddie Mac exempts two-to-four-unit projects and detached condominium units from project review.
• FHA will not work here. FHA single-unit approval requires a project of at least five units, so a house-plus-DADU condominium cannot use it.

On taxes: RCW 64.90.020(2) provides that each unit is separately taxed and assessed once a unit is owned by someone other than the declarant. Before that, the parcel is still assessed as one — which matters for how you sequence a build, and interacts with the improvement exemption covered in does building an ADU raise your property taxes.

Recording the condominium map in King County runs $423.50 for an 18x24 sheet plus $0.50 per additional lot. A sale triggers real estate excise tax — state rates of 1.10% up to $525,000 and 1.28% up to $1,525,000, with those brackets scheduled to rise January 1, 2027, plus Seattle's local 0.50%.

What we will not do is quote you a total for the declaration, survey, legal work and association setup. There is no reliable published figure for a two-unit ADU condominium in Washington, and the range depends heavily on your attorney and how clean the site is. Ask a Washington real estate attorney for a scoped quote early, because the answer determines whether the whole idea pencils.

The tenant trap to know about before you list

If either unit has been occupied by a tenant within twelve months before the first purchase agreement is signed, the project may be treated as a conversion building, which carries notice and tenant-rights obligations under RCW 64.90.655 and, in Seattle, SMC chapter 22.903. This catches homeowners who rent the cottage for a couple of years and then decide to sell it. If selling separately is even a possibility, talk it through before you sign a lease — and see renting out your ADU for how the rental side works.

Does it pencil? What the City's own data shows

Seattle's Office of Planning and Community Development tracks this. In its 2023 report, 44 percent of ADUs permitted in Seattle in 2022 — 416 of 942 — were on condominium parcels, up from 8 percent in 2019. Homeowners and small builders are clearly already using this structure at scale. The same report put the median sale price of an ADU sold as a condominium in 2022 at $757,500, against $1.18 million for the principal unit.

Those are 2022 numbers and not a forecast for your property. The useful signal is structural rather than numeric: a detached cottage on its own title has a much wider buyer pool than a rental unit attached to someone else's house, and it opens an exit that does not require selling the home you live in. Whether that premium justifies the legal and survey cost is the calculation worth doing before you break ground, not after — and it sits alongside the more conventional math in is an ADU a good investment.

Decide this before you design, not after

A DADU built with a future separate sale in mind is a different set of drawings from one built purely as a rental. Things that are cheap at design stage and expensive later:

• Independent utilities. Separate meters and clean service separation make a condominium far simpler to govern and much easier for a buyer's lender. See ADU utility connections for what can and cannot be separated.
• Genuinely independent access to the cottage that does not cross space a buyer would consider private to the house.
• Parking and refuse arrangements that work for two unrelated households, documented in the declaration rather than improvised.
• Clear physical unit boundaries — a detached cottage is far easier to define in a declaration than a converted basement.

This is one of several reasons a detached unit tends to be the cleaner product; the trade-offs are in ADU vs. DADU.

Build it so the option stays open

We build DADUs across King and Snohomish County, and we would rather know at the feasibility stage that a separate sale is on your mind than find out at framing. It changes utility routing, unit boundaries and sometimes where the cottage sits on the lot — all cheap decisions early.

Start with a feasibility conversation about your lot, or look at the cost side first with our ADU cost calculator and what a DADU costs in Seattle.

Again: this is general information about how the code and statutes read, not legal advice, and nothing here creates an attorney-client relationship. Before you rely on any of it, have a Washington real estate attorney review your specific property — and confirm the current rules, which have changed three times since 2023.