The question I get on every build-to-rent conversation is the same: what does it actually cost, and what do you actually get? Fair, because the content you'll find on this topic is long on strategy and suspiciously short on invoices.
So here are four of our own projects, with the real numbers, including the parts that went sideways. All are Washington State infill builds; costs and values are as of my December 2025 deep dive on them.
The Four Projects
| Project | Cost | Value complete | Multiple | Equity created | Annual rent | Unlevered ROI |
|---|---|---|---|---|---|---|
| Shop-to-Airbnb conversion | ~$130,000 | ~$525,000 | ~4x | ~$395,000 | ~$42,000 (conservative) | 32% |
| Stacked-ADU duplex | ~$350,000 | ~$900,000 | ~2.5x | ~$550,000 | ~$53,000 | ~15% |
| Walk-back duplex | ~$375,000 | ~$800,000 (conservative) | ~2x | ~$425,000 | ~$53,000 | 14% |
| Flip + duplex (boundary-line deal) | ~$335,000 | $660,000 | ~2x | ~$325,000 | ~$48,000 | 14% |
The shop conversion is the outlier and the poster child: a shop that rented as storage for $500 a month for six years, converted under Washington's new DADU rules into a themed Airbnb with a barrel sauna and fire pit, three minutes from the water. It became Timber & Tide, modeled conservatively at $42,000 a year with a projected range up to $60,000. Four-times multiple on cost because the structure and land already existed.
The stacked-ADU duplex is a 25x40 two-story box behind two small houses we own, on an alley. Stacked units aren't ideal, but the lot gave us no other option, and here's my favorite line item: by legally designating the building as "stacked ADUs" rather than a duplex, we pay no sewer or water capacity fees and get about half off traffic and park fees, worth roughly $40,000. I'm willing to call it stacked ADUs for a $40,000 difference.
The walk-back duplex sits behind an existing duplex on a dead-end street with no alley: all parking in front, rear units reached by a 4-foot walkway. Code actually required zero parking (near a bus stop, units under 1,200 sqft), but real tenants have real cars, so we built parking anyway, on pervious pavers specifically to avoid triggering onsite drainage requirements. Limited access caps the rents, but the lot was free because we already owned the front property.
The flip + duplex was the elegant one: a house that came with an extra adjacent lot. Boundary line adjustment, roughly $40K into the house, flipped it to an owner-occupant, which effectively made the buildable lot free. A fourplex physically fit, but the fourth unit would have triggered full frontage improvements (curb, gutter, sidewalk) plus an ADA unit, so the math told us to build the duplex instead. I like to have the math tell me what to do. Refinanced out all our money plus about $150,000, cash flowed about $1,000 a month, and later sold and 1031-exchanged into a 14-unit out of state. It sat on the MLS for 45 days before we bought it. Nobody else wanted it.
What Things Cost Per Foot
Costs vary wildly by region and finish level, so anchor points rather than gospel: a garage conversion runs $80,000 to $150,000 all-in depending on energy code, egress, electrical, and plumbing. Our ground-up DADU cost is close to $250 per square foot, helped by years of sub relationships; duplexes come in slightly lower per foot thanks to economies of scale on roofing, insulation, and paint. And the Midwest paradox: cheapest labor in the country, but ARVs so low the finished product is often worth only what it cost to build. The screen that protects you: duplex values around $500K+ with all-in build costs capped near $275-300K (where to find lots like that).
What Went Wrong (So You Can Plan For It)
Honest ledger, same projects. The shop conversion's permitting took 12 months, including 5 months lost to a structural engineer, because almost nobody wants to touch existing-structure work ("we'll help you if you want to build new"). The city didn't penalize the shop's unpermitted history but required full current-code compliance, including energy code, which meant furring up and building a floor over the concrete slab: about $7,000 nobody budgeted.
The fixes we now use on every project: bid structural engineers wide (we emailed about 17 of them; quotes for the same few pages of calcs ranged $8,000 down to $2,300) and always ask turnaround time alongside price, because a $300-cheaper engineer who's four weeks out is expensive. Use a drafter instead of an architect when under four units and the municipality allows it: our duplex plans cost $450 from our drafter against $9,000 architect quotes, delivered in days. And buy in winter: sellers who've sat get realistic (we tied up a deal $30,000 under asking the day before the December call), permits process over spring, you build all summer, and the product hits the market in early fall.
How we pay for all of this without touching our low-rate first mortgages is its own article.
FAQ
Q: How much does it cost to build a DADU? A: Our ground-up cost runs near $250 per square foot in Washington with established sub relationships; garage conversions run $80,000-150,000 all-in. Regional labor, finish level, and code requirements (especially energy code) swing these materially.
Q: Is build-to-rent profitable for small investors? A: Our four current infill projects created roughly $325,000 to $550,000 of equity each, at 14-32% unlevered returns on cost. The margin comes from owning or cheaply controlling the land and building only where finished values comfortably exceed build costs.
Q: What are the biggest risks in small-scale building? A: Permitting timelines (our conversion took 12 months to permit), slow structural engineers, code surprises on conversions, and unit-count thresholds that trigger expensive requirements like frontage improvements and ADA units. Bid vendors wide and let the math pick the unit count.
Q: Why call a duplex "stacked ADUs"? A: Classification drives fees. As ADUs, one of our projects avoids sewer and water capacity fees entirely and pays about half the traffic and park fees, roughly $40,000 saved on an identical building. Ask your planner what each label costs before you apply for permits.
This article is educational and reflects my own projects and markets. It isn't financial advice, and past results don't predict future ones. Run your own conservative numbers and consult the right professionals before building.
