ADU Construction Planning in Bothell, WA

Bothell creates an easy jurisdiction mistake. County location matters for some services and records, but City of Bothell property is reviewed through the City’s Community Development process. A Bothell mailing address outside City limits may use a different authority.

This independent page is not the City, either county or a contractor. Confirm the parcel authority first.

What does Bothell publish for ADUs?

Bothell’s Housing Choices page describes attached units, units above garages and detached ADUs. It notes that ADUs usually share utilities with the primary home. The City’s Applications and Forms page provides a residential Accessory Dwelling Unit application, listed as form 3f.

Bothell also updated housing rules in response to HB 1337. Check the current code and application rather than relying on an older middle-housing FAQ.

How should jurisdiction be confirmed?

Record the situs address, parcel number, incorporated-city status and county. If the property is outside Bothell city limits, identify whether King County, Snohomish County or another city reviews it.

Then collect:

• zoning and existing legal units;
• proposed attached, detached or conversion path;
• lot dimensions and site plan or survey;
• trees, slope, critical areas and drainage;
• construction access and staging;
• water, sewer and power authorities; and
• easements or private restrictions.

Use the King County jurisdiction guide if the southern part of the market creates uncertainty.

What lot conditions should be checked?

Bothell properties can include mature trees, slopes and suburban drainage systems. Review the buildable area, tree protection, driveway and side-yard access, retaining conditions, stormwater and utility routes before choosing a footprint.

For a garage conversion, inspect slab, moisture, structure, ceiling height, fire separation and service capacity. For a detached unit, check excavation access, foundation assumptions and the distance to services.

The feasibility guide provides one property checklist for each option.

What permit and design work should be assigned?

The team should identify the City ADU application, building plans, site plan, structural and energy work, mechanical/plumbing information and any tree or critical-area material. Ask who handles application intake, corrections and issued-set updates.

A pre-drawn or prefab design may reduce some design work, but Bothell must still review the property and current code. Confirm which documents are reusable and which are site-specific.

Use the design and permits guide to turn “permit handling” into named tasks.

How should shared utilities be evaluated?

Bothell says ADUs usually share utilities with the primary home. Shared does not mean no design or cost. Confirm electrical load, water capacity, sewer route, heating, shutoffs, metering arrangements and maintenance access.

Map trenching and restoration. If the project crosses a driveway, tree-root zone or public right of way, record the extra coordination. The utilities and site-work guide lists the items to include in a comparable proposal.

How much does a Bothell ADU cost?

The fresh local demand study found stable but small ADU search volume and soft competition; it did not establish one price. Use the Seattle-area cost guide to create a full budget.

Separate feasibility and survey, design, engineering, permits, access, foundation, structure and envelope, utilities, finishes, restoration and contingency. Ask providers to state whether their price is a shell, a standard finish package or a move-in-ready unit.

How should Bothell providers be compared?

Verify the contracting entity in Washington L&I and confirm service territory for the exact address. Request recent Bothell or nearby ADU projects and identify the permit authority for each example.

Give providers the same property file, design basis and finish schedule. Use the builder comparison to review project evidence, document responsibility, utility work, exclusions, schedule, payment and written warranty terms.

Build a Bothell jurisdiction and utility record

Save evidence that the parcel is inside Bothell city limits and identify the water, sewer, power and fire authorities for the address. County location alone does not answer those questions. Record the official City application and code pages used, with the date checked.

If a mailing address sits outside City limits, stop using the Bothell checklist and confirm the actual county or city permit path. This early record prevents the design and estimate from being built around the wrong forms or utility assumptions.

What should a Bothell site plan show before bids?

Show existing and proposed buildings, setbacks, access, trees, grades, drainage and utility routes. Mark where excavation equipment, concrete placement, storage and waste removal can occur while the main home is occupied. For shared services, show the proposed connection and shutoff arrangement rather than writing only “tie into existing.”

Provide this plan with the same finish schedule to each bidder. Require separate inclusions for design, City corrections, permits, foundation, utility work and restoration.

What must be reconciled at permit issuance?

Compare the approved drawings and permit conditions with the priced set. Document changes to foundation, energy systems, drainage, tree protection or utilities and agree on the cost and schedule effect. Keep approved revisions and inspection records in the owner’s project file.

How should County-line assumptions be communicated?

Write the city-limit confirmation at the top of the project brief and repeat the actual utility authorities in the permit and bid package. Do not let a King County or Snohomish County postal reference substitute for the City of Bothell permit decision.

When requesting project examples, ask whether they were inside Bothell and which utilities served them. A nearby project can demonstrate construction quality while still following different forms, fees and service requirements. Note that distinction in the provider comparison.