Read before you decide.

A second, standalone house on the lot you already own, with its own entrance, kitchen and bathroom. The legal term is a detached accessory dwelling unit — DADU — and Seattle calls them backyard cottages. Most are between 500 and 1,200 square feet, smaller than most people picture. An attached version, built onto your house, is an attached ADU; a garage converted with its own entrance and kitchen counts too.

Probably, and that is new. Washington's 2023 law (RCW 36.70A.681) requires cities and counties inside urban growth areas to allow at least two accessory units on lots where single-family homes are allowed. They cannot cap the size below 1,000 square feet or the height below 24 feet, cannot apply setback or design rules stricter than the ones for your own house, and cannot require off-street parking within half a mile of major transit. The exceptions that matter: lots with wetlands, streams, buffers or steep slopes, and lots without sewer. The free report checks your parcel rather than guessing from the statute.

Now in Washington, with more states coming. Most reports so far are in Snohomish and King County, and the rules matrix behind the report covers 22 Puget Sound jurisdictions; for a property elsewhere in the state the report still runs, and a person checks the local code before it goes out. Outside Washington, leave your address on the form and we'll tell you when your state opens.

You don't have to know. Choose "not sure" on the form. A backyard home follows your city's ADU rules; an addition follows the rules for the house itself (lot coverage, height, setbacks, stormwater) with no pre-approved shortcut; an in-law suite or a garage with its own entrance and kitchen is an attached ADU and follows the ADU rules. The report tells you which set of rules your lot is under and which project has the most room on it.

In the Everett and Snohomish County market a detached unit generally runs $270,000 to $450,000 and up; in Seattle and King County, $300,000 to $650,000. Small units cost more per square foot than large ones, because a kitchen and a bathroom cost what they cost. An attached unit runs roughly $150,000 to $300,000 and a garage conversion roughly $80,000 to $180,000. Those are published market ranges, not a quote for your property; nobody can quote your property until it has been surveyed and designed, and every proposal excludes permits, utility connection fees and Washington sales tax.

Seven to fourteen months from starting design to moving in for a backyard home, and we are not going to soften that. Roughly one to three months is design, two to six is permitting, four to nine is construction. Permitting is the part nobody controls. Some paths are faster — Seattle issues construction permits on its pre-approved plans in weeks, and Everett launched pre-approved designs in 2026 with a three-month target — and additions and conversions have their own ranges, always in months.

Your parcel number, jurisdiction and zoning; the likely setbacks and coverage limits; what is left of your yard after them; slope, trees, utilities and access; whether the project you asked about looks possible at all; which designs could fit; a cost range with each rate sourced; and what to do next. It is preliminary, it says so on every page, and it is not a permit application or an approval. When we say a design is "pre-approved," we mean pre-approved by a specific city on that city's lots; a plan pre-approved in one city is an ordinary plan set in the next.

The second step, and only if you want one. It covers the survey, the site visit, architectural, civil and structural engineering and coordination, and it ends in a fixed-price proposal you can accept or decline. In the builder's current proposals it is a line of the total project price, not a fee in addition to it. It does not include permits, taxes or utility fees. Its amount and payment schedule are stated in the development agreement before you sign. If you decide not to build, the survey, the drawings and the engineering are yours.

No — permits, taxes and utility fees sit outside every proposal. For scale, a 2026 fee calculation on a $250,000 Seattle detached unit came to about $11,779. Everett waives school impact fees on accessory units, waives the transportation fee on the first one, and halves park fees.

Cash, a home equity line of credit, or a construction loan. The one to be careful with is a cash-out refinance, because it replaces your existing mortgage and therefore your rate; if you are holding a mortgage under 4 percent, that is usually the exact thing you were trying to protect. A line of credit or a construction loan sits behind your first mortgage and leaves it alone. We do not lend money and receives nothing for pointing you toward a lender.

Yes, and about a third of accessory-unit owners in Seattle do. Average asking rents in October 2026 for one- and two-bedroom units were $1,577 and $1,875 in Everett, $1,900 and $2,672 in Seattle (Zumper). Rent is not guaranteed, vacancy is real, and you become a landlord. Short-term rental rules are separate and vary by city; do not build on the assumption of nightly income until your city's rules are confirmed in writing.

In Washington, yes, if it is set up as a condominium unit: state law says a city cannot prohibit selling it separately just because it was built as an accessory unit. It is not theoretical — 44 percent of the accessory units permitted in Seattle in 2022 were set up as condominiums. It takes a declaration, a survey and legal work, so decide early rather than late.

Yes. Adding a permitted dwelling is new construction, and the county assessor reassesses for it. Neither we nor your real estate agent can tell you the amount; your county assessor's office can explain how new construction is added to your assessment. Ask before you commit.

Not a vote. This is allowed by state law on most urban single-family lots, so nobody is being asked to approve it, and design standards for your unit cannot be stricter than the ones for your own house. Where neighbors genuinely matter is access: if getting equipment to the back of your lot needs a shared driveway or an easement, that is a real negotiation and it goes much better started early.

We cannot promise you will, and we are careful with this question on purpose. A 2021 national study found homes listed with an accessory unit priced about 35 percent higher than homes without one, comparing asking prices rather than matched sales — directional, not a promise. What nobody can tell you is what an appraiser will credit on your property; the added value may not equal the construction cost. If the only reason to build is the resale number, slow down. If the reason is that you need the space or the income and would rather not move, the arithmetic looks different.

Yes. The report is free and yours, with no obligation to use HousUp's partner builder, or anyone else, for anything. What makes going it alone hard is rarely the framing: it is the survey, design, structural engineering, energy code, land-use review, permit, utility connections, and sometimes a geotechnical or critical-areas report. Soft costs alone run $20,000 to $50,000 in Seattle before construction starts.

Our system pulls your records and sends the report, usually within a few hours. Anything we can't confirm from a desk is listed in it, with the question to ask the builder. We — or a licensed participating builder for your area — may reach out about your report by email, text or phone, to answer questions and, if you would like, set up a visit. The visit matters, because two things a desk study cannot see have cost real money on live projects: driveway access that looks wider on the plat than it is on the ground, and mature trees with no way to get equipment past them. Free, no obligation; you can stop it any time from your project page.