An accessory dwelling unit is the most heavily regulated small building you will ever put on your property, and that is exactly why the builder you choose matters more than the floor plan. The plan is the easy part. The hard part is the year-long chain of feasibility, design, plan review, inspections, and utility coordination that turns a backyard into a legal, rentable dwelling. This is the end-to-end process we run for ADU clients in Beaverton, laid out in order, with the decision points that decide whether your project moves in months or stalls in review.
1. Know your rights: Oregon ADU law in two paragraphs
Oregon is one of the friendliest ADU states in the country. ORS 197.312, expanded by Senate Bill 1051 in 2017, requires cities with more than 2,500 residents to allow at least one accessory dwelling unit per detached single-family home in residential zones, subject to reasonable siting and design regulations. Follow-up legislation barred cities from imposing owner-occupancy requirements or extra off-street parking for ADUs. House Bill 2001, Oregon's middle housing law, layered duplex and multi-unit rights on top for larger cities including Beaverton.
Practically, that means the question in Beaverton is almost never whether you can build an ADU. It is what size, where on the lot, and how the local development code shapes setbacks, height, and design. Those local rules are administered by the City of Beaverton through its development code, and they are where a builder who works here weekly earns their fee.
2. Feasibility before design: the two-week homework phase
Before anyone draws anything, a competent ADU builder checks the things that kill projects late: lot zoning and overlay districts, setbacks and maximum footprint for your specific parcel, sewer and water service capacity (a long utility trench can reshape a budget), electrical panel capacity at the main house, tree preservation constraints, and slope or drainage issues. We also pressure-test the goal itself: a rental ADU, a family suite, and a future aging-in-place unit are three different buildings. This phase costs almost nothing and prevents the expensive version of surprise. Our Beaverton ADU page covers what we check on the first visit.
3. Design and engineering: 4 to 8 weeks
Detached new-construction ADUs need a full drawing set: architectural plans, structural engineering, energy code compliance under the Oregon Residential Specialty Code, and site plans showing setbacks, utilities, and drainage. Garage conversions and basement ADUs are lighter on structure but heavier on egress, ceiling height, and fire separation detail. Converting existing space is usually the fastest path to a legal unit; we compared the paths in our Beaverton ADU permit guide.
4. Permits and plan review: what Beaverton actually reviews
- Building permit application with the full plan set, submitted to the City of Beaverton.
- Planning review against the development code: siting, size, height, design standards.
- Building plan review against the ORSC: structure, energy, egress, fire and life safety.
- Trade permits for electrical, plumbing, and mechanical, pulled by licensed trade contractors.
- System development charges assessed for the new dwelling; Oregon law scales some charges for ADUs, and the numbers change each fiscal year, so verify the current schedule at application time.
- Corrections cycle. Most first submittals draw correction requests. A builder who answers them within days, not weeks, is quietly saving you a month.
Budget 8 to 14 weeks from submittal to permit issuance for a detached unit in a normal review climate, less for conversions.
5. Construction and inspections: 4 to 7 months
Construction runs through the standard inspection ladder: excavation and footings, foundation, underfloor or slab plumbing, framing, rough electrical, plumbing, and mechanical, insulation, drywall, and finals for each trade plus the building final. The certificate of occupancy, or its local equivalent, is the finish line; until it exists, the unit cannot legally be occupied as a dwelling. Between inspections, the sequencing is ordinary construction, but on a compressed footprint where every trade works on top of the next. Site logistics, protecting your yard, your neighbors' patience, and your driveway, are a real skill; ask any builder how they handle staging on a tight lot and listen for a specific answer.
What to ask any ADU builder in Beaverton
- How many ADUs have you taken through Beaverton plan review, and what drew corrections?
- Who does your structural engineering and your energy compliance paperwork?
- What is your current realistic timeline, feasibility to keys, for my lot?
- How do you price and communicate changes once construction starts?
- Are you licensed, bonded, and insured, and can I verify it? (Check any Oregon contractor at ccb.state.or.us, our checklist is in the contractor hiring guide.)
If an ADU is on your list for 2026 or 2027, would it be useful to know whether your lot actually pencils before you spend anything on design? We do free feasibility walks in Beaverton and the surrounding metro, with a written read on siting, utilities, and timeline within 24 hours.
Veteran-owned. CCB #204939. Building ADUs across Beaverton and Washington County, Mon through Sat, 8 AM to 7 PM. Closed Sundays.