The honest 2026 range for a detached backyard ADU: $150,000–$400,000 all-in, with most landing between $200K and $300K. Garage and basement conversions start near $60,000. Per square foot, expect $250–$500 — small buildings concentrate cost, they don't dilute it.
| Path | Typical 2026 all-in | Notes |
|---|---|---|
| Garage conversion | $60,000 – $150,000 | Shell and utilities exist; parking-replacement rules vary |
| Attached ADU / bump-out | $120,000 – $250,000 | Shares a wall and systems; easiest to phase |
| Detached new-build, modest | $150,000 – $280,000 | 400–800 sqft, standard finishes |
| Detached new-build, premium | $280,000 – $400,000+ | Larger, architect-designed, matched to the main house |
The line item that ambushes ADU budgets: utility connections. A long trench, an undersized main panel, or a sewer connection fee can add $20K–$60K before the slab exists. It's the first thing a design-build feasibility pass prices — and the reason internet ADU quotes run fantasy-low.
If the ADU is really phase one of a bigger transformation, read the whole-home remodel guide. Otherwise bring your lot to a free consultation — our firms in your metro know the local ADU code cold, because it's half their inbox.
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A 600 sqft ADU is a complete house — kitchen, bath, HVAC, panel, and utility connections — amortized over very few feet. Small dilutes nothing: $250–$500/sqft is normal, which is how a modest backyard cottage becomes a $250K project.
Cheapest: converting existing space — a garage conversion runs $60K–$150K because the shell, slab, and utilities exist. Most expensive: a detached new-build on a tight urban lot with long utility runs and design review. Prefab units can help, but site work, foundations, and connections still dominate.
In strong rental metros, often yes: $250K financed at 2026 rates against $1,800–$3,000/mo rents can be cash-flow-neutral to positive, while adding appraised value. In cheaper rental markets the math is thinner — run it before you build, and check local short-term-rental rules if that's the plan.
In much of California, Arizona, Colorado, Utah, and a growing list of states and cities, ADUs are now by-right on single-family lots — the 2020-era prohibitions fell fast. Size caps, setbacks, height, and parking rules are hyper-local, which is why feasibility is step one of our process.
Custom homes run $200–$400+ per square foot in major U.S.
Read the guide →Whole-home remodels run $100–$250 per square foot in 2026 — a 2,500 sqft home lands $250K–$600K for a full transformation.
Read the guide →Custom building costs more per square foot than buying used — until you price renovation, compromise, and competition.
Read the guide →