ADU Construction Planning in Bellevue, WA

Bellevue had the clearest secondary demand in the Seattle geo study, with 20 stable monthly searches for the principal ADU construction term. The city page therefore deserves complete local content rather than a Seattle page with the name changed.

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

What changed in Bellevue?

Bellevue’s Middle Housing Code Amendments page says the City Council adopted ordinances in June 2025 to implement Washington HB 1110 and HB 1337. The updates address attached and detached ADUs along with other middle-housing types.

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 developing a program for DADUs and cottage housing in phases. The goal is a set of City-reviewed plans available for purchase. A development program is not a current promise that a plan can be selected and filed today.

Before paying a designer or provider for a “Bellevue pre-approved” plan, request the City program link, plan identifier, current code edition, licence terms and allowed changes. If the plan is not in an operational City program, treat it as a private standard plan that needs ordinary review.

What belongs in a Bellevue lot screen?

Start with zoning and current development, then review:

• number and type of existing homes;
• proposed 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 construction access;
• water, sewer and power service; and
• easements or private covenants.

The 2025 code changes may expand options, but they do not remove building, energy, utility or site requirements. Use the feasibility guide to assemble the property file.

Which permits and documents are likely?

Bellevue’s permit resources say approval and building review can be required when creating an interior ADU or modifying a home. A detached unit or addition carries new-building, site and trade work. MyBuildingPermit is used across many Eastside jurisdictions, but the reviewing city and local code remain Bellevue.

Ask the design team to identify the land-use, building, mechanical, plumbing and electrical submissions; site-plan requirements; energy documents; and correction-response responsibility. The design and permits guide provides a comparison table.

What site and utility issues often affect the scope?

Bellevue properties range from compact neighborhoods to sloped or wooded lots. Tree protection, critical areas, drainage and access can change placement and foundation design. A long sewer route, water work or electrical upgrade can change the budget even when the building plan stays the same.

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

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

How much does a Bellevue ADU cost?

The fresh demand study does not provide a construction price. Online builder ranges mix Seattle and Eastside projects, sizes and finishes. Use the Seattle-area cost guide as a scope framework, then replace every allowance with Bellevue property information.

Budget lines should include feasibility, survey, design, structural and energy documents, permits, site protection, foundation, building shell, utilities, finishes, landscaping and contingency. If a future City plan program reduces design review, show the saving separately rather than assuming it removes site costs.

How should Bellevue providers be compared?

Verify the legal contractor in Washington L&I and request recent Bellevue ADU or comparable residential projects. Ask who obtained permits, who handled corrections and whether the work involved a detached unit, attached addition or conversion.

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

How does Bellevue fit the Eastside decision?

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 property or provider territory is uncertain.

What should be confirmed with Bellevue before plan purchase?

Ask which adopted code and application path control the parcel on the inquiry date. Confirm allowed unit type and size, buildable area, height and lot coverage, and whether tree, critical-area, shoreline or drainage review is likely. If the City has released any pre-approved plans, verify the exact model, code edition, use rights and remaining site documents rather than relying on an announcement about the program.

Save the response with a concept site plan. That plan should show the main home, proposed unit, setbacks, trees, access, utilities and stormwater assumptions. It gives the designer, City and bidders the same question to evaluate.

What should a Bellevue proposal say about MyBuildingPermit?

The proposal should name the Bellevue permit types, who prepares each submission and who responds to corrections. It should distinguish portal administration from professional design and from City fees. If another consultant submits structural, energy, civil or critical-area documents, identify that firm and whether its fee is fixed, allowed 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.