How much does a Star ADU cost?

No — at the same finish level the per-square-foot build cost is essentially identical because most Treasure Valley contractors work both cities. A Standard-finish Kingfisher runs roughly $179k–$222k in either market. Where Star and Boise diverge is permit and impact fees (Star's full fee schedule should be pulled fresh from staridaho.org or by calling the city), HOA review costs in newer Star subdivisions, longer utility runs on acreage lots, and the rent ceiling. Star's median rents run notably higher than Boise's — Rentable reported a Star 1-bedroom average around $1,820/month in April 2026 — which gives Star a real yield edge over the Boise baseline.

The plans physically fit Star lots — all six City of Boise pre-approved designs (Goldfinch, Waxwing, Kingfisher, Kestrel, Sandpiper, Osprey) top out at 695 sq ft, well under any current Treasure Valley size cap, and Star's deeper backyards make siting easy. But the City of Star does not have a formal reciprocity agreement with Boise — your plan set still goes through Star's own permit and zoning review. Idaho Senate Bill 1354, effective July 1, 2026, preempts city-level ADU restrictions for cities over 10,000 population (Star qualifies at roughly 25,660 residents), which loosens local rules but doesn't create automatic plan reciprocity. In practice the same drawings move through faster than a custom design because they're already engineered. Confirm Star's current submittal requirements with the city before you commit to a timeline.

Star publishes its building permit and impact fee figures through the city's Planning & Zoning department rather than a single static schedule we could verify line-by-line. Per-tier dollar amounts depend on building valuation and the current fee schedule — pull the live numbers directly from the City of Star (staridaho.org) before locking your budget. What we can confirm from primary sources: ACHD's transportation impact fee is $5,803/SFD effective 2026-03-01 (ordinance No. 254) and applies in Star the same way it applies in Boise, because ACHD runs a single county-wide service area. Total city plus impact fees on a Treasure Valley ADU typically land in the $8,000–$15,000 band based on builder aggregate experience; verify Star's specific figures with the city before you treat that as final.

Star's permit timeline isn't published as a fixed service-level number we could confirm, so treat any estimate as directional until you've spoken with the city's Planning & Zoning department. A clean, pre-approved-style submittal generally moves faster than a custom design because the drawings are already engineered and detailed. HOA review in Star's newer master-planned subdivisions can add 2–4 weeks running in parallel, not in series, if you submit both packages together. Call the City of Star to confirm the current queue before committing to a date.

Star's current municipal code has required an owner-occupancy affidavit — the property owner or an immediate family member must occupy either the primary dwelling or the ADU for more than six months per year. That changes on July 1, 2026: Idaho Senate Bill 1354 preempts owner-occupancy mandates for cities over 10,000 population, and Star (roughly 25,660 residents) is over that threshold. Cities must update local code to comply by February 1, 2027, so Star's code may still reference the old affidavit until it's revised. Confirm the current status with the City of Star for your specific parcel before signing.

Star rents materially higher than Boise. Rentable reported a Star 1-bedroom average around $1,820/month in April 2026, with two-bedroom averages near $2,260 — well above Boise's roughly $1,479–$1,503 1-bedroom median. Rentable also noted Star's overall median rent running well above Boise City's. That premium reflects Star's status as the fastest-growing city in Ada County combined with a newer, higher-end housing stock. On a Kingfisher (491 sqft, 1BR), Star's higher rent ceiling can lift gross yield meaningfully versus Boise at the same build cost. Run the numbers on the ROI calculator with Star rent inputs — and verify current Star rents directly, since small-market figures move fast — before committing.