ADU Construction Planning in Bellevue, WA

Bellevue has its own ADU and middle-housing rules and is developing a pre-approved DADU program. Owners need current Bellevue guidance rather than Seattle text with the city name changed.

This independent guide is not the City of Bellevue or a contractor. Confirm the current code, filing and site facts directly with Development Services.

What changed in Bellevue?

Bellevue’s housing amendment page says the City Council passed new laws in June 2025. They carry out Washington HB 1110 and HB 1337 and cover attached and detached ADUs.

Older Bellevue pages and PDFs may say detached ADUs were not allowed. Do not use those statements as current rules. Check the adopted code and ask staff how the project is classified.

Does Bellevue have pre-approved DADU plans now?

Bellevue’s Pre-Approved Plans page says the City is building the program in stages. The goal is to offer City-reviewed DADU and cottage plans for purchase. A program under development does not mean plans are ready today.

Before buying a “Bellevue pre-approved” plan, ask for the City link and exact plan ID. Check the code year, use rights and allowed changes. If the City program is not active, treat it as a private stock plan that needs normal review.

What belongs in a Bellevue lot screen?

Start with zoning and current development. Then review:

• number and type of current homes.
• planned attached, detached or conversion route.
• lot dimensions, yards and building coverage.
• trees and possible critical areas.
• slope, drainage and retaining conditions.
• driveway, side-yard and work access.
• water, sewer and power service.
• easements or private covenants.

The 2025 code changes may add options, but building, energy, utility and site rules still apply. Use the early site-check guide to build the site file.

Which permits and documents are likely?

Bellevue says an internal ADU or home change may need review and approval. A detached unit or addition adds new-building, site and trade work. Many Eastside cities use MyBuildingPermit, but Bellevue’s own code still controls.

Ask the design team to list the land-use, building and trade permits. Add site-plan rules, energy records and the person who answers City comments. The design and permits guide provides a comparison table.

What site and utility issues often affect the work?

Bellevue has both compact neighborhoods and sloped, wooded lots. Trees, critical areas, drainage and access can change the unit’s location and foundation. Long sewer, water or power work can raise the price even if the building plan stays the same.

Record current utility companies and approximate routes before requesting a firm quote. Confirm who pays agency fees, performs trenching, restores pavement or landscaping and plans inspections.

Read the utilities and site-work guide before accepting a base building price as complete.

How much does a Bellevue ADU cost?

Online ranges mix Seattle and Eastside projects of different sizes and finishes. They do not price a Bellevue property. Use the Seattle-area cost guide to build a full budget. Then replace each allowance with site facts.

Budget for site checks, a survey, design, structure and energy records. Add permits, site protection, foundation, shell, utilities, finishes and yard work. Keep money for surprises. If a City plan saves design time, show that saving without removing site costs.

How should Bellevue companies be compared?

Check the legal builder in Washington L&I and ask for recent Bellevue ADUs or similar home projects. Ask who got the permits, answered City comments and completed the work.

Give each company the same site facts and plan basis. Normalize design, engineering, permits, site work, service work, allowances, exclusions, schedule and payment milestones. The builder comparison guide explains the evidence to preserve.

How does Bellevue fit the Eastside choice?

Kirkland already advertises a pre-approved DADU program, while Redmond publishes its own ADU and residential-permit material. Those programs do not transfer automatically. Return to the Eastside hub if the site or company territory is uncertain.

What should be confirmed with Bellevue before plan purchase?

Ask which code and filing path control the parcel on that date. Confirm the unit type, size, buildable area, height and lot coverage. Check whether trees, critical areas, shorelines or drainage need review. If City plans are available, verify the exact model, code year, use rights and remaining site work.

Save the answer with a concept site plan. Show the main home, planned unit, setbacks, trees, access, utilities and rainwater path. This gives the designer, City and bidders the same plan to review.

What should a Bellevue quote say about MyBuildingPermit?

The quote should name each Bellevue permit, who files it and who answers City comments. Separate portal work, expert design and City fees. If another firm provides structural, energy, civil or critical-area records, name it. State whether its fee is fixed, an allowance or excluded.

Require a list of unresolved City and utility items at contract signing. A portal status or permit allowance is not a complete description of the remaining work.