How much does a Garden City 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 Garden City and Boise diverge is the zoning code itself (Garden City has its own development code and design-review triggers, separate from Boise's Modern Zoning Code), lot conditions (older riverfront parcels can be narrower with longer utility runs), and the rent ceiling. Garden City's average apartment rent is $1,713/month per RentCafe (June 2026), with 1-bedrooms around $1,553 and 2-bedrooms around $1,754 — broadly in line with Boise.

The drawings physically fit, but Garden City does not honor Boise's pre-approved ADU program — Garden City is a separate municipality with its own code, so any plan set goes through Garden City's own permit and design review, not Boise's fast-track. Garden City has historically capped ADUs smaller than Boise's 900 sq ft (a 600 sq ft limit appeared in earlier code), and a recent ordinance amendment changed those standards — confirm the current size cap and design-review rules with the City of Garden City before assuming any of the six Boise plans (Goldfinch, Waxwing, Kingfisher, Kestrel, Sandpiper, Osprey) qualify. Idaho Senate Bill 1354, effective July 1, 2026, preempts city-level ADU size and owner-occupancy restrictions for cities over 10,000 population, which is likely to loosen Garden City's rules — but the local code update process is still in motion, so verify directly.

Garden City sets its own building permit and impact fees, which differ from Boise's — pull the current schedule directly from the City of Garden City and don't assume Boise's numbers carry over. What we can confirm from primary sources: ACHD's transportation impact fee is $5,803 per single-family dwelling effective March 1, 2026 (Ordinance No. 254), and it applies to Garden City the same way it applies to Boise because Garden City is inside the Ada County Highway District. City-level permit, plan-review, and any local impact fees are set by Garden City — call the Garden City planning office for the live figures before locking your budget. Sewer and water connection fees vary by parcel and provider. Total city plus impact fees on a Garden City ADU typically land in the $8,000–$15,000 band based on aggregate Treasure Valley builder experience, but confirm the Garden City portion directly.

Confirm the current cap with the City of Garden City — it is in flux. Earlier Garden City code limited accessory dwelling units to 600 sq ft, smaller than Boise's 900 sq ft cap, and a recent ordinance amendment revised the ADU standards (including compatibility-with-main-structure requirements and changes to maximum-size language). On top of that, Idaho Senate Bill 1354 — signed March 31, 2026, effective July 1, 2026 — preempts city-level ADU size and owner-occupancy limits for cities over 10,000 population and requires cities to update local code. Because the local size rule may change before your permit, pull the current Garden City standard rather than relying on any published number, including ours.

Verify with the City of Garden City — and note the rule is changing statewide. Garden City's development code has historically included its own ADU conditions, which can differ from Boise's. Idaho Senate Bill 1354 preempts owner-occupancy requirements for ADUs in cities over 10,000 population effective July 1, 2026, with cities required to bring local code into compliance afterward. Until Garden City revises its code, older provisions may still appear on the books. Confirm the current status for your specific parcel and zone with Garden City planning before signing.

Garden City rents track close to Boise, with a slight premium near the greenbelt and the Live-Work-Create district. Per RentCafe (June 2026), the average Garden City apartment rents for $1,713/month, with 1-bedrooms around $1,553 and 2-bedrooms around $1,754 — though published per-bedroom figures vary widely by source (some platforms quote 1-bedroom medians north of $1,900), so treat any single number as a starting point and pull current comps for the specific block. The greenbelt, Esther Simplot Park, and the brewery/winery corridor support tenant demand near the river. On a Kingfisher (491 sqft, 1BR), a Garden City rent ceiling in line with or modestly above Boise keeps gross yield competitive. Run your own rent comps in the ROI calculator before committing.