Hillsboro ADU Builder

The right ADU in Hillsboro starts with the site, not the floor plan

An accessory dwelling unit can be a rental, a place for family, or a home office, but the first question is always what the site and the rules permit. JDI Construction is a family-owned design-build remodeler, and that question is where we begin every ADU: it's a second, independent home on your lot, and the zoning and utilities settle what's buildable before any design does. The Portland metro is generally very ADU-friendly, which tends to help Hillsboro homeowners — but rules still vary by city and jurisdiction, and every lot is its own case, so we confirm what your specific property allows first. Hillsboro spans a lot of ground, from the older streets near downtown to the newer developments that came with the Silicon Forest, and what a lot can hold shifts across those very different neighborhoods.

Our designers and trades work as one team, so the unit you approve is grounded in what the site and the code actually permit — we don't hand a hopeful floor plan to a separate crew and find out later it won't pass. Here's the range of ADUs we build, what decides what's possible, and what to expect on cost and timeline.

The parts that matter most

A successful ADU comes down to a few things done in the right order. These are the parts we focus on from the start:

A few decisions worth making early

The choices that shape an ADU arrive well before design. First is feasibility. The metro's ADU-friendly stance generally helps, but Hillsboro's rules are the city's and the county's, not automatically Portland's, and no two lots are alike once slope, access, and utility locations enter the picture — so we confirm what your parcel permits before anything gets drawn. Second is type and use: a garage conversion, a basement unit, an attached addition, and a detached cottage carry very different costs and site demands, and building for rental income, family, or a workspace steers the layout. Third is budgeting for the invisible work — the sewer, water, and power connections and the system development charges that come with a new dwelling. We cover all of it up front so nothing catches you off guard after design.

What Hillsboro homeowners build ADUs for

The ADUs we hear about in Hillsboro tend toward a few uses: a rental unit that draws on the region's steady housing demand, a private space for aging parents or adult children who want to stay close, or a home office or studio set apart from the main house — a fit for a workforce that increasingly works from home. Each points the design somewhere different: a rental favors durability and a separate entrance, a multigenerational unit favors single-level, step-free living.

Hillsboro's mix of housing works to your advantage. Older lots near downtown may suit a detached cottage or a garage conversion, while newer developments can point toward an attached or interior unit. Whatever the use, we design a compact footprint to live larger than its square footage, using light, storage, and ceiling height to keep a small home from feeling small.

What does an ADU cost in Hillsboro?

ADU cost is driven first by type: a garage or basement conversion that reuses an existing structure generally costs less than a detached cottage built from the ground up. After that come size, finish level, and — the part homeowners most often underestimate — the site and utility work. Extending sewer, water, and power to a new dwelling, handling grading and access, and covering connection fees can take a meaningful share of the budget, which is why we scope it early. With design and trades both in-house, we give you an itemized estimate once we know what your lot allows and which type fits, so the number reflects your project rather than a generic per-square-foot figure.

How long does an ADU take to build?

An ADU runs on three clocks: feasibility and design, permitting, and construction. Permitting for a second dwelling generally takes longer than a remodel because it involves zoning and utility review, so we build that time into the plan instead of promising a quick turnaround. Once permits are issued, construction depends on the type — a conversion is faster than a ground-up cottage. We give you a realistic schedule after the feasibility check, handle the permitting, and keep you updated through our client portal as the unit takes shape.

Why homeowners in Hillsboro choose JDI

An ADU rewards a builder who understands the rules as well as the construction, because the project can stall at the permit counter long before the first wall goes up. As a single accountable design-build team, we handle the feasibility, the design, the utility connections, and the build under one roof, so nothing slips between a zoning question and the crew on site. We manage the permitting, keep you informed through our client portal, and stand behind the work with a five-year workmanship warranty. We're based across the river in Vancouver, a short drive away, close enough to stay responsive through a project this involved.

JDI Construction — "Built by family. Trusted by neighbors." Design-build remodeling and ADU construction based in downtown Vancouver, WA, serving Hillsboro and the greater Portland–Vancouver metro since 2007.