Converting part of your house into a Junior ADU is one of the ways to add living space or rental income here in Portland, but the price tag can be a surprise. When homeowners are looking at an attached garage conversion or carving out a space in a basement down in Sellwood or over in Alberta, they need real numbers, not vague estimates. Mighty ADU Company wants to talk about what a Junior ADU actually costs right now and where the money goes.
The Bottom Line: Typical Price Ranges
Most Junior ADUs in the Portland metro area land somewhere between $75,000 and $150,000. That is a wide spread because the total price depends entirely on what the structure is starting with. A simple interior conversion of an existing finished room with a half-bath might only run $65,000 if the plumbing is right there. On the other hand, turning a damp, unfinished 500-square-foot basement or a drafty garage into a fully self-contained 500-square-foot Junior ADU with a kitchen, separate entrance, and independent HVAC is going to push past $130,000 fast.
What Actually Drives the Cost Up?
Kitchens and bathrooms eat up the bulk of your budget. Cabinets, appliances, counters, and plumbing rough-ins add up quickly. If Mighty ADU Company has to break through a concrete slab foundation to run new drain lines for a kitchen island or a shower, that labor-intensive trenching costs real money.
Electrical capacity is another major factor. Many older Portland homes, especially the classic 1920s bungalows in neighborhoods like Creston-Kenilworth, still run on 100-amp panels. Adding a Junior ADU means you will likely need a service upgrade to 200 amps to handle independent heating, cooking appliances, and modern electrical loads.
Permits and system development charges also play a part. While the city has eased up on some fees for smaller units under 500 square feet, plan check fees, structural engineering reviews, and Bureau of Development Services permits will still chip away at your funds.
What is Included in a Proper Quote?
When Mighty ADU Company puts together a bid, we break it down so you do not have to guess. A solid quote should cover architectural drawings, engineering, permits, structural framing, insulation to meet current energy codes, drywall, flooring, doors, windows, complete electrical and plumbing systems, and finishes. If a contractor hands you a suspiciously low quote, check the exclusions list. They might be leaving out flooring, painting, or utility hookups just to win the bid.
How to Avoid Overpaying
Keep the existing layout mostly intact where you can. Moving a bathroom across the room requires major plumbing surgery. Use mini-split heat pumps instead of extending your main furnace ducts because they are cheaper to install and let tenants control their own climate.
Get three bids, but do not automatically pick the cheapest one. Make sure every contractor is bidding on the exact same scope of work. Ask about their experience with Portland Bureau of Development Services, because dealing with local inspectors efficiently saves you thousands in delay costs. Mighty ADU Company provides Junior ADU construction services for homes in Portland, Oregon.