Accessory Dwelling Unit (ADU) Permit in Idaho Falls, Idaho
VerifiedIdaho Falls permits accessory dwelling units (ADUs) on lots with an existing principal single-family dwelling, per Idaho Falls City Code Title 11, Section 11-2-6(N) (Comprehensive Zoning). ADU construction is processed as a Residential Building Permit or Residential Addition/Remodel Permit through the Cityworks portal, subject to the zoning standards below plus standard 2018 IRC/IBC building code review.
Verified 2026-07-03 · Source
When you need this permit
- ADU may be configured as an integral part of the principal dwelling (any floor or basement), an attached structure, a separate detached structure, or (in Industrial/Commercial zones) a caretaker's residence
- Maximum ADU size: 750 square feet
- Detached ADU must meet the same side-yard setback as the primary structure for the applicable zone
- Detached ADU must have a minimum 12-foot setback from the rear property line, unless adjacent to a public/private alley at least 16 feet wide, in which case Table 11-3-3(3) setbacks apply
- A detached ADU more than 12 feet in height must comply with the height standards of Table 11-3-3(1)
- ADU structure must be well-matched in height, bulk, and site location with the adjoining neighborhood, and (if attached or a separate structure) must share the same architectural design, style, and appearance as the principal dwelling
- ADU must have a separate entrance from the principal dwelling, meet building code requirements for a separate dwelling unit, and be functionally independent
- Recreational vehicles are prohibited as ADUs
- One additional off-street parking space required on the lot (in addition to the principal dwelling's existing minimum); a garage may not be converted to an ADU unless replacement parking is provided elsewhere on the lot
- The property owner must occupy either the principal dwelling or the ADU as their primary residence; this owner-occupancy requirement is enforced through a deed restriction recorded with the Bonneville County Recorder
- Only one ADU is permitted per lot of a principal dwelling unit; ADUs are not counted in density calculations
- The ADU may not be sold separately or converted to a legal ownership form different from the principal dwelling
Required documents
- Required
Cityworks Residential Building/Remodel Permit Application
Standard residential permit application via Cityworks, noting ADU scope of work
- Required
Deed Restriction (Owner-Occupancy)
Recorded with the Bonneville County Recorder to enforce the owner-occupancy requirement of Idaho Falls City Code § 11-2-6(N)(4)
- Required
Site Plan
Showing ADU location, setbacks, and required parking space per Idaho Falls City Code § 11-2-6(N)
Fee schedule
| Fee type | Amount | Notes |
|---|---|---|
| Residential Building Permit Fee — valuation-based (same schedule as new construction/addition) | $30.18 minimum ($1-$499 valuation), scaling per the Residential Building Permit Fee Valuation Table | City of Idaho Falls Fee Schedule (October 2025), item 2.6; no dedicated ADU fee line was found separate from the standard residential valuation table |
Review timeline
10–10 business days
Idaho Falls’s published plan-review target
Inspection process
- 1
Footing/Foundation
For detached ADU construction, before concrete pour
- 2
Framing
Structural framing per approved plans
- 3
Mechanical, Electrical, and Plumbing Rough-In
Combined MEP rough-in for the ADU's independent systems
- 4
Final
Combined Building, Mechanical, Electrical, and Plumbing final inspection, including verification of the separate entrance and functional independence from the principal dwelling
Tips
- Idaho Falls' ADU ordinance requires owner-occupancy of either the principal home or the ADU, enforced by a deed restriction recorded with the Bonneville County Recorder — this is a durable, recorded obligation that survives a sale unless removed.
- Converting an existing garage into an ADU is not permitted unless the required parking is relocated elsewhere on the lot.
- Detached ADUs over 12 feet tall trigger additional height standards under Table 11-3-3(1) of the Zoning Code — confirm applicable table values with the Planning Division before finalizing design.
Frequently asked questions
- How big can an accessory dwelling unit be in Idaho Falls?
- A maximum of 750 square feet, per Idaho Falls City Code § 11-2-6(N)(2)(a). The property owner must occupy either the principal dwelling or the ADU as their primary residence, enforced via a recorded deed restriction with the Bonneville County Recorder.
Sources & verification
Verified against official sources. Last reviewed 2026-07-03.
- City of Idaho Falls Building Division (Department of Community Development Services) — official building department
- Idaho Falls City Code Title 11 — Comprehensive Zoning (PDF)
- Apply for a Permit | City of Idaho Falls
- 2025-2026 Fee Schedule (PDF) | City of Idaho Falls
- Idaho Code § 39-4117 — Processing Building Permits — Timely Review (added 2025 ch. 272; 10 business days residential / 20 commercial for completeness determination, which 'shall not constitute approval')
Fees, timelines, and adopted codes are researched from each jurisdiction's published records — see how we verify. Requirements change and vary by project, so always confirm the current details with the Idaho Falls building department before you submit. PermitBase is an independent reference and is not affiliated with any government agency.
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