Blaine County allows detached ADUs and tiny homes on wheels as ADUs, and Idaho’s new state ADU law (SB 1354) took effect July 1, 2026. SwagerBuilds builds fixed-price ADUs in Sun Valley, Ketchum, Hailey, Bellevue, and unincorporated Blaine County — detached, garage-conversion, or guest-house style. Zoning-verified before you sign.
What just changed with ADUs in Idaho
Two rule changes matter for Sun Valley property owners:
- Idaho SB 1354 was signed March 31, 2026, and took effect July 1, 2026. Cities of 10,000+ population must remove bans on ADUs in residential zones by February 1, 2027. Ketchum, Hailey, Bellevue, and Sun Valley are all under 10,000 so this doesn’t force them directly — but the state signal is clear on direction.
- Blaine County Ordinance 2025-08 (passed 8-26-2025) allows detached ADUs and tiny homes on wheels as ADUs in unincorporated Blaine County. Max ADU size is 50% of the gross floor area of the principal structure without a conditional use permit.
Rules for Ketchum, Hailey, Bellevue, and Sun Valley proper vary. We verify your specific lot’s rules before quoting.
Types of ADUs we build in the Wood River Valley
- Detached ADU (stand-alone small home). 400–1,200 sqft on its own foundation, its own utilities, its own address.
- Attached ADU / mother-in-law suite. Attached to the main home, often over an attached garage.
- Garage-conversion ADU. Converting an existing detached garage into a legal ADU. Zoning-sensitive.
- Guest house / accessory structure. Non-ADU accessory unit — no kitchen, no rental. Faster permit path but limited use.
Real fixed-price cost ranges — Sun Valley ADU, 2026
- Basic garage-conversion ADU (500–700 sqft): $150,000–$250,000
- Detached ADU (600–900 sqft) with utilities separate: $325,000–$500,000
- Detached luxury ADU (900–1,200 sqft, design-review lot): $500,000–$750,000
- Attached ADU over garage: $200,000–$400,000 depending on size and finishes
Sun Valley ADU cost per square foot runs $500–$700 for detached because you’re carrying full utility sets, foundation, and finish on a small footprint. Bigger is more efficient per foot.
Design review + permit — the parts that matter for ADUs
- Ketchum: Detached ADUs require design review. Roof form and siding must match the primary structure per the new Land Development Code effective 2026-01-01.
- Hailey: Materially lighter outside historic overlays. Faster path than Ketchum on comparable ADUs.
- Bellevue: Standard IBC review.
- Unincorporated Blaine County: Ordinance 2025-08 governs. Max 50% of principal structure GFA without CUP. Mountain Overlay + Scenic Corridor overlays still apply for design review.
Sun Valley ADU FAQ
Can I build a detached ADU in Ketchum in 2026?
Depends on your zone. Ketchum’s new Land Development Code (effective 2026-01-01) governs. Some zones allow detached ADUs by right; others require a conditional use permit. We verify your specific lot before quoting. Confirm with Ketchum Planning & Building at 208.726.7801.
How big can an ADU be in Blaine County?
In unincorporated Blaine County, maximum ADU size is 50% of the gross floor area of the principal structure without a conditional use permit (Ordinance 2025-08). Larger with a CUP.
Does the new Idaho ADU law (SB 1354) apply to Sun Valley?
SB 1354 requires cities of 10,000+ population to remove ADU bans in residential zones by 2027-02-01. Ketchum, Hailey, Bellevue, and Sun Valley are all under 10,000 so SB 1354 does not automatically force them. Local rules still govern. Verify current code with each city before you buy a lot expecting an ADU right.
How much rental income does a Sun Valley ADU generate?
Depends on furnishing, location, and short-term-rental rules (which vary by city). Do not build an ADU expecting Airbnb income without confirming short-term-rental status for your zone — several Wood River zones restrict or ban STR. Long-term rental income is safer to underwrite against.
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