ADU Construction in Greater Seattle & the Eastside
HB 1337 rewrote ADU construction rules statewide. Many restrictions that blocked homeowners before 2023 no longer exist.
- HB 1337 compliant
- Buildable envelope mapped first
- 3D site layout included
- WA Lic #ANYVIHR768KB
Washington changed the ADU rules — here’s what that means for your lot
HB 1337 set a new statewide floor for what cities can and cannot require from property owners building an accessory dwelling unit.
An ADU is a self-contained living unit on a residential lot. Before this law, your city could require you to live on-site. It could require you to add off-street parking. It could cap your unit smaller than the state allowed. Most of those restrictions are gone now.
What hasn’t changed: the permit pathway still requires real work. ADU construction still involves land use review, building permit approval, and utility connection sign-off. The rules got more favorable. The process didn’t disappear.
If you looked into building an ADU in the past and encountered restrictions that stopped the project, your lot may qualify now under rules that didn’t exist when you last checked.
Five ADU types, one permit pathway, a different build on every lot
Homeowners and property investors across the region have several distinct ADU options, each with its own construction approach.
DADU — detached ADU. A fully separate living unit on the same lot as the main house, not physically connected to the primary residence. Under HB 1337 a DADU can typically be up to 1,000 square feet — or up to 1,200 depending on lot size and applicable local rules. Local zoning codes still govern setbacks, height, and lot coverage.
AADU — attached ADU. A self-contained unit sharing at least one wall with the main residence: basement apartments, converted ground-floor wings, or additions built onto the back of an existing home. It has its own private entrance, kitchen, and bathroom, and typically involves more MEP coordination than a detached build.
Garage conversion. Converts an existing attached or detached garage into a permitted dwelling unit. No new foundation is required, which reduces cost — but the scope still includes insulation, framing to living-space standards, electrical upgrades, plumbing rough-in, and a full permit pathway. If your property sits within a half-mile of a major transit stop, HB 1337 means you are not required to replace the parking space you’re converting.
Casita. A detached ADU often designed for visiting family, aging parents, or short-term guests. It follows the same zoning rules as a standard DADU, but typically emphasizes single-storey accessibility, high-end guest finishes, and indoor-outdoor connection to the main yard.
Multi-family ADU. For investors or owners of existing duplexes and townhomes, recent zoning updates create pathways to add detached units or convert non-livable spaces such as shared garages into additional rental units on a multi-family lot.
What I see when we walk a lot for the first time
The 52 square feet they didn’t get was never going to be buildable on that parcel — and we confirmed that before they spent a dollar on design.
I walked a project last spring on a corner lot in Redmond. The homeowner wanted a detached ADU in the backyard — about 800 square feet. They had a sketch on their phone and a rough budget in mind. The lot looked straightforward from the street.
When I pulled the parcel data, the setback situation was more complex than it appeared. The rear setback under local zoning was eating into the footprint they had imagined. We couldn’t hit 800 square feet without pushing into the side setback on the east-facing lot line. That wasn’t obvious until we ran the numbers.
What that meant practically: a contractor who went straight to drawings without checking setback calculations first would have produced a design that couldn’t be permitted. We catch that at the parcel review stage, not at the city counter.
What we did instead: I mapped the buildable envelope on their specific parcel before we touched the 3D design. The homeowner saw exactly what footprint was achievable on their lot — not a generic layout, but the actual shape that would clear every setback, stay within lot coverage limits, and pass land use review. The final unit came in at 748 square feet. It got permitted. Construction finished in four months. That’s the difference between knowing the code and approximating it.
One question that comes up on every ADU estimate call
Homeowners regularly ask whether they must live on the property to build or rent an ADU. Under current Washington law, they do not.
Before HB 1337, Washington cities could require the property owner to occupy the home as their primary residence before they could legally build or rent an ADU. That requirement — called owner-occupancy — was removed statewide.
It means you can own an Eastside or Seattle property, build a DADU on it, and rent both the main house and the ADU without being required to live on-site.
What this changes practically: ADU construction is now a highly viable investment for a wider group of property owners, not only those who plan to stay in the home long-term.
How Anyvision builds ADUs
Every Anyvision ADU project starts with a buildable envelope review and a full 3D site layout before a single permit application is filed.
Permit pathway review first
We identify which approvals apply to your specific lot — land use, building permit, utility connection — before design work begins.
3D site layout and floor plan
You see the actual footprint, interior layout, and exterior appearance on your lot before construction documents are filed.
HB 1337 compliance built in
Size limits, parking exemption eligibility, and owner-occupancy removal are incorporated at the design stage.
W-2 crew, no subcontractors
Foundation, framing, MEP rough-in, insulation, drywall, and finish work all performed in-house.
WA Lic #ANYVIHR768KB
Covers every permit application we file on your behalf.
Daily WhatsApp updates
A photo or video from the job site every day the crew is on-site.
From parcel review to certificate of occupancy
What’s actually buildable
Before we draw anything, we pull parcel data, calculate your buildable envelope under local setback and lot coverage rules, confirm transit proximity for the parking exemption, and identify which permit pathway applies.
Jurisdiction pathway
Seattle ADU permits run through SDCI. Redmond projects follow the RZC, and Bellevue projects go through Bellevue Development Services. These are not interchangeable processes. We work in all of them regularly.
Design and permit
Once the envelope is confirmed we produce the 3D floor plan and site layout. You approve the design. We file the application — drawings, site plan, fees, and all city correspondence managed by our team.
Build
For a DADU: foundation, framing, roofing, MEP rough-in, insulation, drywall, finish. For a garage conversion or AADU we work within the existing shell — framing to living-space standards, electrical upgrades, plumbing rough-in, interior finishes.
Inspections and certificate
Framing, MEP rough-in, insulation, and final inspections are each scheduled and passed before the next phase. The certificate of occupancy — the document that makes your ADU a legal, rentable housing unit — is the last step.
Areas we serve
Anyvision builds ADUs across Greater Seattle and the Eastside.
Our office is in Redmond, and we work across the SR-520 and I-90 corridors daily, serving Seattle, Bellevue, Redmond, Kirkland, Sammamish, and the surrounding King County markets. Call 425-515-5796 to confirm your location falls within our service radius.
- Redmond
- Seattle
- Bellevue
- Kirkland
- Sammamish
- King County
Ready to see what’s buildable on your lot?
Anyvision delivers a 3D site layout and permit scope review before any construction documents are filed.
Include your parcel address and the ADU type you’re considering — DADU, AADU, casita, garage conversion, or multi-family.
Prefer to write? Email info@anyvision-homeremodeling.com or submit your project details through the estimate form. We respond within 24 hours.
ADU construction questions
Do I have to live on the property to build or rent an ADU?
No. Before HB 1337, Washington cities could require the property owner to occupy the home as their primary residence before building or renting an ADU. That owner-occupancy requirement was removed statewide.
You can own a property, build a DADU on it, and rent both the main house and the ADU without living on-site.
How large can my ADU be?
Under HB 1337 a detached ADU can typically be up to 1,000 square feet, or up to 1,200 depending on lot size and applicable local rules.
The state preempted many restrictions, but local zoning still governs setbacks, height, and lot coverage — which is why we map the buildable envelope on your specific parcel before any design work.
Do I need to replace the parking space if I convert my garage?
Not if your property sits within a half-mile of a major transit stop. That parking exemption under HB 1337 applies specifically to garage conversions.
We confirm transit proximity during the parcel review, before design begins.
Which ADU type is right for my lot?
There are five common paths: a detached DADU, an attached AADU sharing a wall with the main house, a garage conversion, a casita designed for guests or family, and multi-family ADUs on duplex or townhome lots.
Which one is viable depends on your parcel’s setbacks, lot coverage, and existing structures — that’s what the buildable envelope review determines.
How long does an ADU build take?
One recent Redmond DADU finished construction in four months after permit approval. Total duration depends on the permit pathway for your jurisdiction, since Seattle SDCI, Redmond RZC, and Bellevue Development Services are not interchangeable processes.