Beaverton ADU permits are not the bureaucratic maze most homeowners imagine. They are a sequence of well-defined steps that can move quickly if your submittal is complete and slowly if it is not. After building accessory dwelling units across Washington County for years, here is the honest map: pathway, realistic timeline, what drives cost, and the three early design choices that decide whether your ADU actually pencils out as a rental.
Three ADU types, three permit pathways
Before any conversation about cost or timeline, you have to know which of the three ADU types you are building. Beaverton treats each differently, and each comes with its own design, engineering, and inspection sequence.
Internal ADUs convert existing space inside the primary home into a second dwelling unit. Most common version: a basement build-out with its own entrance, kitchen, and bath. This is usually the fastest and cheapest pathway because the building envelope already exists. Egress, ventilation, and fire separation are the technical hurdles.
Attached ADUs add new conditioned space onto the existing home, sharing at least one wall. These trigger more involved structural engineering because you are tying new framing into existing framing, and they trigger more thorough energy code review.
Detached ADUs are standalone structures — a new small house in the back yard. They require land use review (setbacks, lot coverage, height), new foundation work, new utility runs, and full structural engineering. They are the most expensive path and they almost always have the highest rent ceiling.
The Beaverton permit sequence, step by step
- Pre-application research. Pull your zoning, verify lot size, check setbacks, confirm height limits, and look up sewer and water capacity. This is where we save weeks for homeowners — most of the questions that derail permits get answered here, before a designer touches a sheet.
- Land use review (detached and some attached). Demonstrates that the proposed structure complies with zoning, setbacks, lot coverage, and parking. Detached ADUs almost always need this; internal almost never do.
- Design and engineering. Architectural plans, structural calculations, energy code compliance, mechanical and plumbing layouts. We do this in-house because we have a full-time licensed architect on payroll and formal partnerships with structural, civil, and geotechnical PEs.
- Building permit submittal. Plans go to the City of Beaverton for plan review. This is where incomplete packages bleed weeks. A complete package on first submittal is the single highest-leverage thing you can do.
- Plan review and corrections. The city returns comments. Some are clarifications, some are real corrections. You respond and resubmit.
- Permit issuance and construction. Work proceeds with inspections at framing, mechanical rough-in, insulation, and final.
- Final inspection and certificate of occupancy. The unit becomes legally rentable on the date of final occupancy approval.
Realistic timeline by ADU type
| ADU type | Permit timeline (typical) | Construction timeline |
|---|---|---|
| Internal conversion | 6 to 10 weeks | 8 to 14 weeks |
| Attached addition | 8 to 12 weeks | 14 to 22 weeks |
| Detached standalone | 10 to 14 weeks | 16 to 26 weeks |
Timelines assume a complete first submittal, prompt response to plan review comments, and no land use appeals. Add four to eight weeks if any of those are not true.
The three design choices that decide if it pencils
The math on an ADU as a rental is sensitive to three early design choices. Most homeowners do not realize how much these decisions tilt the project's economics until the contractor numbers come back.
Choice 1: Where the bathroom and kitchen stack
Plumbing cost is dominated by how far new fixtures are from existing sewer and water lines. Stacking the ADU bathroom directly above or below an existing bathroom is a meaningful cost reduction. Pushing the ADU kitchen to the far corner of a detached structure means trenching, longer drain runs, and bigger venting headaches. We always run the floor plan past the plumbing layout before we commit.
Choice 2: Whether you bury new utility services
Detached ADUs need power, water, and often a new sewer connection. Trenching to the right of way for new service is one of the largest single line items. If the lot is sloped, has mature trees, or has paved driveways in the trench path, the cost climbs fast. Sometimes sharing utilities with the primary home — when code allows — saves five figures.
Choice 3: Roofline complexity
A simple gable roof costs roughly half what a multi-hipped, dormered roof costs at the same square footage. The architectural temptation is to match the primary home. The financial reality is that every additional ridge, valley, and dormer is real money for the same interior square footage.
"A complete package on first submittal is the single highest-leverage thing you can do. It saves weeks, sometimes months, and it costs the same as a sloppy one."
— Gabriel Horta Blancas, Owner
What slows a Beaverton ADU permit down
In our experience, the avoidable delays cluster in five places: missing structural calculations, energy code worksheets that are not signed by the right credential, ambiguous setbacks on the site plan, missing land use approval before building permit submittal, and unclear utility connection drawings. Every one of those is an in-house process problem on the design side, not a city problem.
We submit complete packages the first time because we have an architect on payroll, formal partnerships with structural, civil, and geotechnical PEs, and a CCB #204939 license at the residential and commercial level. We are not subbing the engineering out to whoever is cheapest that week.
What we do before we quote you a number
- Walk the property with the owner, look at the proposed location, check slope and access.
- Pull the zoning, setbacks, lot coverage, and height limits for the specific parcel.
- Verify sewer, water, and electrical service capacity at the existing meter.
- Confirm tree preservation requirements and any easement constraints.
- Discuss the three design choices above, in plain English, with the rent target in mind.
Then we write a number you can build a budget around — not a guess, not a national average, not a "ballpark" that grows by 40 percent at contract.
If you are considering an ADU this year
Start with a free consultation. We will tell you whether your lot supports an ADU at all, which type makes sense, and what realistic permitting and construction looks like for your specific property. If we are not the right fit, we will say so. Veteran-owned, family-built. CCB #204939. Architect on payroll. We are open Mon through Sat, 8 AM to 7 PM. Closed Sundays.