150+ backyard homes completed across Seattle, the Eastside and Tacoma
Two units per lot are now allowed statewide. Owner occupancy is gone. Parking mandates are gone. If someone told you your property wouldn't take one, they may have been reading rules that no longer exist.
Five questions. A real cost range back, plus what a unit that size rents for near you.
Zoning, lot coverage and setbacks are all parcel specific. We can't give you a real answer without it.
We look at every parcel ourselves before anything goes back out.
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$500, credited against your build agreement.
The cheapest real path we can deliver is a garage or basement conversion, and those start around $150,000 once permits, utility connections and Washington sales tax on labour are in. Below that we'd be cutting something that matters. Send us a note and we'll point you to two builders we'd trust with a smaller scope.
Ask for a referralTakes about 60 seconds. No obligation.
Design, permitting and construction under one roof. We work with homeowners who already own the property. Rain City ADU is a trading brand of Rain City Restoration LLC, licensed, bonded and insured in Washington, registration RAINCRL752C8. Serving Seattle, Bellevue, Kirkland, Redmond, Mercer Island and Tacoma.
The second lot is the one worth understanding. In Seattle, converting a structure that already exists can be permitted despite lot coverage and setback limits that would stop a new build on the same ground. Two identical looking back yards, two completely different answers.
House Bill 1337 rewrote the floor for every city in Washington planning under the Growth Management Act. Seattle then went further with Ordinance 127376, which took effect in January 2026. If your information predates that, here's what moved.
One accessory unit per lot
Two accessory units per lot, statewide
You had to live on the property
No owner occupancy requirement
Off street parking required
No parking mandate for an accessory unit
A height cap written specifically for backyard cottages
In Seattle, accessory units now follow the same standards as the main house, so height comes from your zone
A garage conversion had to fit within lot coverage and setbacks
In Seattle, converting a structure that already existed can be permitted despite those limits
A no from 2023 was an answer about a rulebook that has since been replaced twice.
The number that breaks a backyard home project is almost never the one on the drawings. It is a sewer line further out than anyone checked, a tree with a protected root zone, a foundation that has to step down a slope.
On a unit this size those carry further than they would on a whole house, because there is less budget to absorb them. They are the line items that turn a $340,000 project into a $460,000 one, and every one of them is findable before you sign anything.
We find them in the feasibility study, price them into the design, and hold the number.
Every figure below is the final contract price, not the starting estimate.
Ballard, Seattle
Her mother sold the family house in Renton and had eight months before the sale closed. The brief was a real one bedroom, a real kitchen, and a door her mother could lock behind her.
Kirkland
A 1954 garage they had used for storage for two decades. Two builders had quoted a teardown and rebuild. The structure was sound, so we kept the footprint and the slab and converted it instead.
North End, Tacoma
The lower floor had been storage since 1961. Because the lot falls away at the back, we could cut a full-height entrance at grade rather than sink a stairwell, and the existing waste stack ran within a few feet of the new bathroom. Feasibility found both before anyone drew anything.
Here's what a permitted backyard home actually requires. The right column is what you'd be coordinating yourself.
| Scope | Rain City ADU | The usual path |
|---|---|---|
| Zoning and lot feasibility | In-house, before design | You find out during permitting |
| Lot coverage and floor area modelling | In-house | Architect, once you've hired one |
| Architectural design | In-house | Separate architect, separate contract |
| Structural engineering | Coordinated by us | You coordinate |
| Cost estimating during design | In-house, weekly | Doesn't happen. Pricing comes after drawings. |
| Tree retention and drainage review | In-house feasibility | Discovered at plan review |
| Permit filing | We file | Architect files, or you do |
| Permit corrections | We handle every cycle | Back and forth between architect and city |
| Utility connections and sewer capacity charge | Priced in from the start | Usually excluded from the quote |
| Construction and daily supervision | Our team on site | Varies |
| Warranty and service | Us | Whoever's still in business |
Eleven line items. One phone number.
One project manager from first sketch to final walkthrough. Not a call centre, not a rotating account rep, not "let me check with the architect and get back to you."
Free
Five questions about your back yard and what you want it for. You get a real cost range for that path in your city, and what a unit that size currently rents for nearby.
$500
We pull your parcel and walk the site. You get a written report: what your lot legally allows under the current code, where the unit can sit, lot coverage and floor area modelled, tree retention, drainage and critical area exposure, utility routing and the sewer capacity charge, a costed budget range, and an estimated rental return. Yours to keep, whether or not you build with us.
Credited
If the feasibility works and you want to proceed, we present a full agreement. Your $500 is credited against it.
Why we charge for it. Seattle's pre-approved plan library is genuinely useful, and it clears the building. It does not clear your lot. The plan licence alone runs up to $1,000, and a custom architectural set that turns out to be unbuildable on your parcel is $8,000 to $15,000 you don't get back. The $500 is what you spend to find out which of those is worth spending. It is also the cheapest thing on this page by a factor of several hundred.
In Seattle, 1,000 square feet for up to two bedrooms and 1,200 for three or more, with a larger allowance in some transit-served lowrise situations. Tacoma caps at 1,000 square feet or 85 percent of the main house, whichever is smaller. Your lot's coverage and floor area limits often bind before the size cap does, which is exactly what the feasibility study models.
Permit review is the pacing item and it varies more than anyone likes. A pre-approved plan can clear in weeks. A custom design on a straightforward lot takes longer, and a critical area, steep slope or tree retention issue takes longer again. Total design to move-in usually runs 10 to 18 months. We build on site, so we can't compress permitting and we won't tell you we can.
Because the building is only part of the cost. Site work, foundation, utility connections and the King County sewer capacity charge move the number more than finishes do. Washington also charges sales tax on construction labour as well as materials, roughly 9 to 10.25 percent, which is why quotes that look cheaper often haven't included it. Ask anyone who gives you a number whether permits, site prep and utility connections are in it.
Under state law, yes, two accessory units are allowed per lot. Whether your particular lot fits two is a different question, and it usually comes down to coverage and floor area rather than permission. Worth modelling before you assume either way.
Over a long horizon, often. Quickly, rarely. A detached unit in Seattle at current median rents takes well over a decade to return its build cost in gross rent, before maintenance, vacancy and the property tax increase. Anyone quoting you a fast payback is either using gross rent as if it were profit or leaving the build cost out. We'd rather you saw the real arithmetic in the report and decided from there.
Yes, entirely. We file and manage every correction cycle. You will not be chasing the city.
We're not a lender, but we can help you explore your options. The feasibility report is built to be handed straight to one when you're ready to have that conversation.
Five questions, a real cost range, and an honest answer about whether it's worth going further.
Check my lot