Planning Bellevue DADU builder permits now requires current information. Bellevue adopted middle-housing code changes in 2025 that expanded the housing types allowed in residential areas, including detached accessory dwelling units. Older pages or articles saying detached ADUs are categorically unavailable should not guide a new project.
Allowance in the code does not mean every backyard accepts the same building. Feasibility still depends on the parcel, existing units, zoning, setbacks, easements, critical areas, access, utilities, building design, and the documents requested during review. Start with property facts before selecting a floor plan or promising a construction date.
Confirm the current housing framework
Bellevue’s official middle housing code amendment page explains that the 2025 updates implemented state requirements for attached and detached ADUs along with other housing types. Review current code and speak with city staff about the actual parcel because summaries cannot resolve site-specific questions.
A Bellevue ADU and addition builder can coordinate early construction input, but land-use feasibility and permit requirements should be verified before design commitments. Record the date and source of each regulatory conclusion so later decisions do not rely on an obsolete rule.
Build a parcel fact sheet
Collect the legal description, survey or reliable boundary information, zoning, lot area, existing structures, unit count, impervious surfaces, recorded easements, utility records, access conditions, and any known critical areas. Note discrepancies between records and field conditions for investigation rather than choosing the most convenient version.
Map trees, grade changes, retaining walls, driveways, drainage paths, service meters, sewer or septic information, overhead lines, and the spaces needed to construct the unit. A backyard that looks open from a patio can be constrained by property rights or infrastructure below and above ground.
Measure setbacks from the right references
Bellevue explains on its building setbacks page that measurements commonly relate to property lines, while rights-of-way, access easements, critical areas, and district rules can alter the analysis. Do not measure only from a fence, curb, or visible pavement.
Show roof eaves, stairs, landings, equipment, decks, and other projecting elements along with the main walls. Ask which items count toward setbacks, lot coverage, or other limits. A floor plan that fits as a rectangle may fail when the complete exterior assembly is drawn.
Test utility routes before fixing the layout
Trace plausible paths for water, sanitary sewer, storm drainage, power, communications, heating or cooling equipment, and any required metering. Identify slopes, trench depth, crossings, capacity questions, and restoration areas. Place bathrooms, kitchens, and service spaces with those paths in mind.
A garage-conversion cost study offers a useful comparison point when an existing structure could be reused. A detached unit may preserve the garage but require more site and utility work; the decision belongs to the property, not a generic preference.
Design construction access alongside resident access
Draw how excavation equipment, concrete, framing, windows, roofing, and finish materials reach the work area. Protect the main home, landscaping, utilities, neighbors, and emergency routes. Tight access may change equipment, labor, staging, temporary fencing, and the sequence of site restoration.
Then design the permanent walk from parking or street to the new entrance. Consider lighting, drainage, steps, gates, privacy, waste storage, mail or deliveries, and how residents pass the main house. Construction access disappears; daily access must work for years.
Coordinate the DADU with the main property
Locate windows and outdoor areas to balance daylight with privacy for both households. Review views into bedrooms, kitchens, patios, and neighboring yards. Include mechanical equipment, roof runoff, refuse storage, fencing, and landscape screening so the site plan represents actual use rather than only building footprints.
The Bellevue DADU design ideas guide develops these small-home decisions after basic feasibility is established. Keep design alternatives open until setback, access, and utility constraints are credible.
Assemble one coordinated permit set
The drawings should consistently show existing and proposed conditions, site dimensions, floor plans, elevations, sections, structure, energy measures, utility work, drainage, and required details. Discipline-specific sheets must use the same building location, openings, equipment, and revision date.
Use the Bellevue garage-conversion permit guide only when evaluating an existing garage; its structural and change-of-use questions differ from a detached new-building path. Keeping the two scopes separate prevents topic and document confusion.
Carry approvals into site operations
Before work begins, review permit conditions, required inspections, protected site features, erosion or drainage measures, approved utility routes, and any limits on access. Place inspection holds in the schedule before concrete, framing, utilities, insulation, or finishes conceal relevant work.
Keep a current site plan and decision log during construction. If trenching encounters an unknown service, grade conditions change, or a protected feature limits equipment movement, pause the affected work and coordinate the response. Confirm whether a revision or additional review is required, update cost and schedule implications, and communicate the accepted solution to every crew whose work depends on it.
A property-specific Bellevue DADU estimate request should include the fact sheet, photographs, intended use, target size, access observations, and unresolved feasibility questions. Include any survey, title, or utility information already available, with its source and date. That produces a responsible starting discussion without representing an early concept as an approval.