ADU Builders Seattle Checklist: 12 Things to Verify Before Signing a Contract

# ADU Builders Seattle Checklist: 12 Things to Verify Before Signing a Contract

Most homeowners in SeaTac and across King County spend weeks researching accessory dwelling units before they talk to a single contractor. Then they sign a contract in under an hour. This ADU builders Seattle checklist exists to close that gap and protect your investment before a single permit is pulled.

Licensing and Insurance: What Seattle ADU Builders Must Carry

Before you take any contractor seriously, verify these four things.

Washington State Contractor License. Every ADU builder working in Seattle must hold a valid license through the Washington State Department of Labor and Industries. You can verify any contractor's license at lni.wa.gov in under two minutes. If a builder hesitates to give you their license number, that tells you something.

General Liability Insurance. Minimum $1 million per occurrence is standard for residential construction. Ask for a certificate of insurance, not just their word. The certificate should name you as an additional insured for the duration of the project.

Workers' Compensation Coverage. If an uninsured worker is injured on your property, you can be held liable. Washington State requires workers' comp for any employer with one or more employees. Ask for proof.

Surety Bond. Washington requires licensed contractors to carry a surety bond. This protects you if the contractor walks off the job or fails to pay subcontractors. Check the bond amount and confirm it is current.

Any reputable ADU builders in Seattle will have all four of these ready before you even ask.

Portfolio and References: What to Actually Ask Past Clients

A portfolio tells you what a contractor can build. References tell you what it was actually like to work with them.

When reviewing a portfolio, look for projects that match your scope. A builder who specializes in full ADU and DADU builds will approach your project differently than someone who mainly does bathroom remodels. Ask to see before-and-after documentation, not just finished photos staged for a website.

When calling references, skip the generic questions. Ask these instead.

Did the project finish on schedule? If not, why, and by how many weeks?

Were there cost overruns? If so, were they explained in advance or did you find out at billing?

How did the builder handle problems when they came up? Every construction project hits a snag. What matters is how the team responded.

Would you use them again for a larger project? This question tends to get honest answers.

Three references is a minimum. Five is better. Any builder confident in their work will give you more than you ask for.

Contract Red Flags: Vague Scopes, Missing Timelines, and Lien Waivers

This is where homeowners lose money. A vague contract is not a minor inconvenience. It is a liability.

Watch for a vague scope of work. If the contract says "build ADU per client specifications" without a detailed list of materials, dimensions, finishes, and systems, you have no legal footing when the finished product does not match your expectations. Every line item should be spelled out.

Missing timelines. A legitimate contract includes a project start date, a substantial completion date, and defined milestones in between. If a builder refuses to commit to timelines in writing, expect delays.

No lien waiver provision. If your builder does not pay their subcontractors or material suppliers, those parties can file a lien against your property even if you already paid the general contractor in full. Conditional lien waivers should be exchanged at every draw payment. This keeps your title clean.

Unclear change order process. Changes happen on every project. The contract should define how changes are requested, priced, and approved in writing before any additional work begins.

Read the contract twice. If something is unclear, ask for it to be rewritten in plain language before you sign.

Permit Responsibility: Who Pulls and Manages Them?

In Seattle, ADU permits are not optional and they are not simple. The City of Seattle requires permits for detached ADUs (DADUs), attached ADUs, and most structural additions. The process involves zoning review, structural plan review, and inspections at multiple phases of construction.

Here is what to confirm in writing before you sign anything.

Who is the permit applicant? The contractor should pull permits in their name, not yours. If a contractor asks you to pull your own permits, they may not be properly licensed, and you absorb the liability that comes with it.

Who manages the inspection schedule? Inspections are time-sensitive. A builder who misses inspection windows creates delays that compound across the entire project timeline.

What is the estimated permit timeline? Seattle permits for DADUs can take anywhere from several weeks to several months depending on project complexity and current city workload. A builder who promises a start date without accounting for permit lead time is not being straight with you.

Is the design permit-ready? Some contractors start design work before confirming it meets Seattle's ADU code requirements. You want a builder who designs with permit approval in mind from day one, not one who revises plans after the fact.

Any experienced ADU builders in Seattle will have a defined permit process and a track record of approvals to show for it.

Payment Schedule: How a Legitimate ADU Builder Structures Draws

How a contractor asks to be paid tells you a lot about how they run their business.

Avoid large upfront payments. A deposit of 10 to 15 percent is reasonable to cover mobilization and early material costs. If a builder asks for 30, 40, or 50 percent before work begins, treat that as a serious warning sign.

Expect draw-based payments. Legitimate contractors bill in phases tied to completed milestones, not arbitrary calendar dates. Common draw points include permit approval, foundation complete, framing complete, rough inspections passed, and substantial completion.

The final payment should be held until the end. Ten percent retained until final inspection and punch list completion is standard practice. This gives you real leverage to make sure every item gets finished correctly.

Get lien waivers at each draw. As covered above, conditional lien waivers should accompany every payment. This is not optional. It protects the title on your property throughout construction.

If a contractor's payment schedule does not align with project milestones, ask why. A clear, direct answer is a good sign. Vague justifications are not.

Frequently Asked Questions

What permits are required to build an ADU in Seattle? Most ADU projects require a construction permit, and detached ADUs typically require a full building permit covering structural, mechanical, electrical, and plumbing work. Your builder should manage the entire permit process, from application submission to final inspection sign-off.

How long does it take to build an ADU in Seattle? From signed contract to move-in, plan for 12 to 18 months on a detached ADU in the Seattle area. That includes design, permitting (which alone can take 3 to 6 months), and construction. Builders who quote 6 months without a permit approval already in hand are not giving you an accurate picture.

How much does an ADU cost in Seattle? Costs vary based on size, site conditions, and finish level. A basic DADU in the Seattle area typically starts around $200,000 and can exceed $400,000 for larger, high-performance builds. Passive House-certified ADUs carry higher upfront construction costs but deliver significantly lower energy and operating costs over the life of the building.

What is the difference between an ADU and a DADU in Seattle? An ADU (accessory dwelling unit) is any secondary living unit on a residential property. A DADU (detached accessory dwelling unit) is a freestanding structure separate from the main home, often called a backyard cottage. Attached ADUs share a wall with the primary residence. Both are permitted under current Seattle zoning rules, though setback and size requirements differ.

How do I use the ADU builders Seattle checklist before signing a contract? Keep it open during every contractor meeting and go through each item one by one. Ask for documentation, not just verbal assurances. Do not sign anything until you have verified licensing, insurance, a relevant portfolio, solid references, clean contract terms, a defined permit process, and a milestone-based payment schedule. The ADU builders Seattle checklist works best as a live tool during the hiring conversation, not something you review after the ink is already dry.

Ready to Build Your ADU the Right Way?

Love Construction serves SeaTac and the greater Seattle area with Passive House construction, custom ADU and DADU builds, home additions, and full remodels. We pull our own permits, put everything in writing, and have references ready to share before you ask.

If you are ready to move forward or just want straight answers before committing to anything, reach out at loveconstructionseattle.com/contact. A real conversation about your project, with no pressure attached.