Detached ADUs, mother-in-law suites, second-story additions, and room expansions — designed, permitted, and built by a licensed Washington general contractor with 11 years of experience. One team, start to finish.
Whether you need a detached ADU for rental income, a mother-in-law suite for aging parents, or more square footage for a growing family, we build it from the ground up — or up from what you already have.
Stand-alone accessory dwelling units up to 1,000 sq ft with their own kitchen, bathroom, and entrance. Perfect for long-term rentals, guests, or a private space for family. We handle foundation, framing, all systems, and finish work.
An ADU built onto your existing home with a separate entrance — great for mother-in-law suites and multigenerational living. We tie into existing utilities where it makes sense and keep your primary living space undisturbed.
Convert unused airspace over an existing or new garage into a full living unit. Great for smaller lots in Auburn, Kent, and Renton where footprint is limited. We verify the foundation and framing can carry the load before breaking ground.
Turn an unfinished basement into a legal, code-compliant ADU or in-law suite. Includes egress windows, insulation, moisture control, separate entrance, kitchen, and bath. Typically the fastest path to added living space.
Add a full second floor to a single-story home — bedrooms, bathrooms, and bonus space without expanding your lot footprint. Includes structural engineering, new roof system, and weatherization planning so your home stays protected during the build.
Add a primary suite, home office, dining expansion, or family room. Bump-outs extend an existing room 2 to 15 feet without the complexity of a full addition — a cost-effective way to gain usable square footage.
ADUs and additions are some of the most complex residential builds. You want a contractor who's done this before, pulls the permits correctly, and actually shows up.
Ziv Construction has been building and remodeling in South King County since 2015. Owner Ihar runs every project personally — no subcontracted project managers.
Washington State Contractor License #CCZIVCOCI856P2. Fully bonded and insured, so your property and investment are protected the entire build.
We handle site surveys, plans, engineering, and submittal to Auburn, Kent, Renton, Federal Way, Puyallup, and surrounding jurisdictions. No back-and-forth for you.
Foundation, framing, electrical, plumbing, HVAC, drywall, finish — coordinated under one roof. You call one person when you have a question, not five.
Typical ranges in the Auburn market for ADU and addition projects across Kent, Renton, Federal Way, and Puyallup. Every project is different — we provide detailed, itemized estimates so you know exactly where every dollar goes.
| Project Type | Typical Range |
|---|---|
| Basement / garage conversion ADU | $100k – $150k |
| Attached ADU (400–700 sq ft) | $150k – $250k |
| Detached ADU (up to 1,000 sq ft) | $250k – $350k |
| Above-garage ADU | $200k – $300k |
| Room addition / bump-out | $40k – $120k |
| Second-story addition | $200k – $400k |
Major cost drivers: square footage, foundation type, utility distance, site slope, kitchen and bath finish level, and whether the unit ties into existing services or needs a separate meter. We walk through every line item before you sign anything.
An ADU has more moving parts than a standard remodel — site planning, permits, utilities, build, and final inspection. From first consultation to final sign-off, most ADU projects in Auburn run several months to a year. Design and permitting add 2-4 months on top of build time in South King County. Every project gets a written schedule that maps out each step so there are no surprises.
Many ADU and addition projects pair naturally with interior remodels on the main house. Here's what else we do.
Pair a new ADU build with a kitchen refresh on the main home. Cabinets, countertops, layout redesign, and appliance upgrades.
Add a primary suite bath during a second-story addition, or upgrade existing bathrooms while the crew is on-site.
See all the neighborhoods we cover in Auburn — Lea Hill, West Hill, Lakeland Hills, and more — and why homeowners here are adding ADUs.
Permit timelines, cost breakdowns, and rental math — helpful reads while you're planning your project.
The questions we hear most from homeowners in Auburn, Kent, Renton, and across South King County.
Most ADUs in Auburn cost between $150,000 and $350,000 fully built. Basement or garage conversions start around $80,000 to $150,000. A detached new-construction ADU up to 1,000 sq ft typically lands at $250,000 to $350,000, depending on finishes, site conditions, and utility hookups. Permit fees, design, and sewer/water connections are separate line items we break out in every quote.
Yes. Washington state law now allows ADUs in all residential zones, and Auburn permits detached ADUs up to 1,000 square feet on most single-family lots. Owner-occupancy rules have been relaxed statewide. Each city — Kent, Renton, Federal Way, Puyallup — has slightly different setback, height, and parking rules, and we handle the research and permitting for your specific lot.
ADU projects typically take several months to a year from first consultation to final inspection, with permitting and design adding 2-4 months on top of build time in South King County.
Yes. We manage the full process — site survey, architectural drawings, structural engineering, and submittal to the City of Auburn (or whichever jurisdiction applies). We coordinate with planners on setbacks, height limits, and utility connections, and we handle revisions until the permit is issued. You get a single point of contact from design through final inspection.
Yes. Under current Washington law, ADUs can be rented long-term in all residential zones, and most cities in South King County now allow short-term rentals as well (subject to local registration rules). ADUs are a popular option for rental income, multigenerational housing, or a mother-in-law suite. We'll design the layout to match your intended use.
We serve a 25-mile radius from Auburn — including Kent, Federal Way, Renton, Puyallup, Maple Valley, Covington, Enumclaw, Bonney Lake, Sumner, and Tacoma. Each jurisdiction has its own ADU rules and permit process, and we're familiar with all of them.
Free on-site consultation, honest budget, and one contractor managing the entire build. Call or email to get started.
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