ADU Cost in Twin Falls, Idaho
What it really costs to build an ADU in Twin Falls — by type, with Twin Falls-specific permit fees, rent, and ROI. Straight from local ADU builders.
Quick Answer
An ADU in Twin Falls, Idaho typically costs $80,000 – $150,000 for a garage conversion, $150,000 – $350,000 for a detached new build, and $150,000 – $280,000 all-in for a pre-fab/modular unit (roughly $150 – $300 per square foot finished). Add permits and impact fees on top.
ADU Cost by Type in Twin Falls
| ADU Type | Typical Twin Falls Cost | Timeline | Best For |
|---|---|---|---|
| Garage Conversion | $80,000 – $150,000 | 2–4 months | Lowest cost; existing garage in good shape |
| Detached New Build | $150,000 – $350,000 | 4–8 months | Maximum size + design flexibility |
| Pre-Fab / Modular | $150,000 – $280,000 | 8–14 weeks on-site | Faster on-site; straightforward lots |
| Per square foot (finished) | $150 – $300 / sq ft | ||
Permits & Fees in Twin Falls
$250 Zoning Use Permit + building/trade permits + Idaho impact fees (~$6k–$10k). Under SB 1354, ADU fees may not exceed those for a single-family home.
These are in addition to the construction cost above. We get exact fee quotes from the local office for your specific project during the Feasibility Check — see our full line-item cost breakdown + ROI calculator for how the numbers add up.
Rental Income & ROI in Twin Falls
A 1-bedroom ADU in Twin Falls typically rents for $900–$1,400/month long-term (estimate). At this rate, an ADU often offsets much or all of its financing payment within a few years, on top of the 20–30% property value increase ADUs typically deliver (per FHFA research).
Want the exact numbers for your property and goals? Our free eligibility check tells you your maximum ADU size, and the Feasibility Check gives you a good/better/best budget for Twin Falls.
More for Twin Falls Homeowners
ADU Rules in Twin Falls
Zoning authority, size limits, setbacks, and SB 1354 status for Twin Falls County.
Full Cost Breakdown
13-category line-item breakdown + interactive ROI calculator.
Am I Eligible?
Instant check: your max ADU size + which floor plans fit your lot.
Financing
HELOC, construction loan, cash-out refi — and Idaho lender options.
Get Your Real ADU Budget for Twin Falls
Start with a free 10-15 minute Readiness Call, then book a Feasibility Check for a detailed good/better/best budget tailored to your property.