Bellevue Preapproved ADU Plans: Could Your Backyard Cottage Get Easier to Build?

A Bellevue backyard cottage sounds simple until the drawings, drainage questions, and invoices arrive. Suddenly, the little house has a surprisingly large to-do list.

Bellevue wants to shrink part of that list. Its October 15 announcement invites public input on a program that would offer preapproved designs for detached accessory dwelling units, or DADUs, and cottage housing.

The important word is “would.” Bellevue preapproved ADU plans are still being developed. There is no confirmed catalog ready to buy today.

Instead of commissioning an entire design from scratch, homeowners could purchase a plan the city has already reviewed. Bellevue is considering up to 10 selected designs across DADUs and cottage housing, sold at predetermined prices.

That could reduce repeated design work and building-code review. Today, a custom project brings its own drawings through that process.

This program builds on housing types Bellevue already allows. It does not make every backyard buildable.

The city’s program outline lists DADUs up to 1,200 square feet and cottage homes up to 1,500 square feet, both capped at 24 feet for this program. Those are different housing categories, not interchangeable size allowances.

Current code also allows certain DADUs above existing accessory structures to reach 28 feet. Bellevue says garage-overbuild designs will be excluded from the standardized program because existing buildings vary too much.

For a new detached unit, the dimensional standards generally require five-foot side setbacks. Front setbacks range from 10 to 25 feet and rear setbacks from 10 to 15 feet, depending on zoning. Structural coverage is generally 40% or 45%, depending on the district.

Those limits apply alongside floor-area limits, tree protections, easements, drainage, and critical-area rules. The city’s site-plan guidance explains that coverage includes existing buildings and certain decks, too.

For example, 40% of a qualifying 8,000-square-foot lot is 3,200 square feet of total structural footprint. Your existing house and garage have already spent some of that allowance.

One caution: the online code flags pending amendments. Check the adopted 2026 ordinance and confirm your parcel’s rules before paying for drawings.

Bellevue has not announced plan prices or a verified average savings figure.

For a local reference point, Kirkland-based Piper Cole Architects publishes an architecture and design range of $15,000–$60,000 for Eastside ADU projects. That is one firm’s stated range, not a Bellevue-wide average or a quote for your project.

Here is illustrative budget math: if custom design costs $25,000 and a future plan license plus site adaptation costs $10,000, the difference is $15,000. Both are assumptions, not announced Bellevue program prices. Compare equivalent scopes and budget separately for any engineering, survey, permits, and utilities excluded from either option.

A cheaper drawing package does not make excavation cheaper. Dirt remains stubbornly unimpressed by paperwork.

Pre-review could reduce questions about the standard building design. Site-specific work would remain: placement, foundation suitability, utilities, drainage, trees, access, and any environmental constraints.

Major changes to a standard plan could also require additional review. Bellevue has not published a guaranteed turnaround for this program.

The March 10 Council minutes identify fall 2027 as the anticipated completion of the final phase. Treat that as a planning target, not a reservation for a construction crew.

The city is gathering preferences through its survey. Design selection, technical review, and public launch still follow. Check the program page for the survey and future participation opportunities.

Kirkland offers preapproved plans with licensing up to $1,000, plus separately billed site adaptation. Renton offers free base plans. Seattle’s ADUniverse program is established, with 15 newly selected designs targeted for public use in January 2027.

None of those prices or timelines automatically carries over to Bellevue.

If you need space for family soon, start feasibility and design discussions now. If your timing is flexible and a standard layout could work, following the catalog’s progress makes sense. Any property-value benefit depends on the finished project and market; design savings alone do not establish resale value.

For a Bellevue homeowner considering an ADU, the practical first step is a parcel check. Find out what fits, what utilities will cost, and whether your schedule can accommodate the city’s developing program.