Additions & new builds.
We build home additions, ADUs, and ground-up structures in Hillsboro and Washington County — taken from permit to move-in with a single point of contact, like our Tigard ADU.
Additions and new builds are where clear communication matters most: permits, engineering, inspections, and a months-long schedule all have to line up. We manage the full arc — design and permitting, foundation, framing, mechanical/electrical/plumbing through trusted subcontractors, and every finish — while you deal with exactly two people: Timothy and Rachel.
Accessory dwelling units are a specialty. Washington County allows one ADU of up to 900 square feet (or 75% of the main home's floor area, whichever is smaller) in most residential zones, with no owner-occupancy requirement — making an ADU a strong option for family or rental income. Our Tigard ADU went from permit to move-in under one roof, one contract, one contact.
From our projects.
Good to know.
In most residential zones, yes. Washington County allows one accessory dwelling unit up to 900 square feet or 75% of the main home's floor area, whichever is smaller, and there is no owner-occupancy requirement — so an ADU can be used as a rental. We handle feasibility, permitting, and construction as one project.
Plan on several months end-to-end: design and permitting typically take 1–3 months in Washington County, and construction another 3–6 months depending on size and complexity. We give you a written schedule with the contract and communicate immediately when anything shifts.
Tell us about your project.
Email us a few sentences about what you're hoping to build — we'll schedule a walk-through, then write up and send a detailed estimate.
estimates@callahancustom.com