Accessory Dwelling Unit (ADU) Permit in Idaho Falls, Idaho

Idaho Falls requires an accessory dwelling unit (adu) permit for: 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. If your project isn't listed, confirm with City of Idaho Falls Building Division (Department of Community Development Services) at 208-612-8270 before starting work.

In Idaho Falls, the published Residential Building Permit Fee — valuation-based (same schedule as new construction/addition) is: $30.18 minimum ($1-$499 valuation), scaling per the Residential Building Permit Fee Valuation Table. These are the jurisdiction's own published figures — see the fee schedule table and source citations on this page.

Idaho Falls's published plan-review target for an accessory dwelling unit (adu) permit is 10–10 business days.

You'll need: Cityworks Residential Building/Remodel Permit Application; Deed Restriction (Owner-Occupancy); Site Plan. See the required-documents checklist on this page for details on each.

Idaho Falls requires 4 inspection(s) for an accessory dwelling unit (adu) permit, in order: Footing/Foundation, Framing, Mechanical, Electrical, and Plumbing Rough-In, Final. Schedule each through City of Idaho Falls Building Division (Department of Community Development Services) (208-612-8270).

Apply through City of Idaho Falls Building Division (Department of Community Development Services) at 380 Constitution Way, P.O. Box 50220, Idaho Falls, ID 83405. Phone: 208-612-8270, email: rhall@idahofalls.gov. Office hours: Building Division, 380 Constitution Way, Idaho Falls, ID 83405 (mailing: P.O. Box 50220, Idaho Falls, ID 83405); main line 208-612-8270. Official information: https://www.idahofallsidaho.gov/269/Building.

Idaho Falls, Idaho has adopted: Idaho has a mandatory statewide baseline building code under the Idaho Building Code Act (Idaho Code Title 39, Chapter 41), administered locally by certified jurisdictions. The City of Idaho Falls independently administers its own Building Division (Department of Community Development Services) and adopts its own codes and amendments by ordinance under Idaho Falls City Code Title 7 (Building Regulations), rather than relying on the Idaho Division of Building Safety for direct administration. Source: Idaho Falls City Code Title 7, https://www.idahofallsidaho.gov/DocumentCenter/View/139/Title-7---Building-Regulations-PDF; 2018 International Building Code (IBC), published by the International Code Council, adopted as the official building code of the City per Idaho Falls City Code § 7-1-1, with local amendments in § 7-1-2 (e.g., day-care/custodial-care occupancy classifications, relocatable building provisions). Source: Idaho Falls City Code Title 7, Chapter 1; 2018 International Residential Code (IRC) for One- and Two-Family Dwellings, including Appendix M, adopted per Idaho Falls City Code § 7-6-1, with local amendments in § 7-6-2 (e.g., owner-occupied lodging house exceptions, Table R301.2(1) design criteria, Section R405.1 exception). Source: Idaho Falls City Code Title 7, Chapter 6; Idaho State Plumbing Code, adopted statewide in 2017 pursuant to Idaho Code Title 54, Chapter 26, and adopted as the City's official Plumbing Code per Idaho Falls City Code § 7-5-1, with local amendments in § 7-5-2 (Chapter 1 replaced with 2018 IBC Chapter 1; fixture-count table cross-referenced to the City's 2018 IBC). The Idaho State Plumbing Code is based on the Uniform Plumbing Code (per City of Idaho Falls Plumbing page, citing epubs.iapmo.org/2017/Idaho/) and is administered at the state level by the Idaho Division of Occupational and Professional Licenses (DOPL) Plumbing Bureau for licensing, but permits within Idaho Falls city limits are issued and inspected by the City's own Building Division, not DOPL. Source: Idaho Falls City Code Title 7, Chapter 5; City of Idaho Falls Plumbing page; National Electrical Code (NEC), adopted per Idaho Falls City Code § 7-8-1 as "the same National Electric Code adopted by the State of Idaho pursuant to Idaho Code Section 54-1001" (Ord. 3627, 9-11-25); the City of Idaho Falls Electrical page identifies the currently adopted edition as the 2023 NEC (NFPA 70). Electrical permits within Idaho Falls city limits are issued and inspected by the City's own Building Division (Chief Electrical Inspector and Electrical Inspector on staff), not the Idaho DOPL Electrical Bureau. Source: Idaho Falls City Code Title 7, Chapter 8; City of Idaho Falls Electrical page and staff directory; 2018 International Mechanical Code (IMC) and 2018 International Fuel Gas Code (IFGC), per the City of Idaho Falls Mechanical page's Documents, Codes & Resources list. Mechanical/HVAC permits within Idaho Falls city limits are issued and inspected by the City's own Building Division (Chief Plumbing/Mechanical Inspector and Mechanical Inspector on staff). Source: City of Idaho Falls Mechanical page; 2018 International Energy Conservation Code (IECC), adopted per Idaho Falls City Code § 7-11-1, with local amendments in § 7-11-2 (industrial/manufacturing equipment exemption; large-building air-leakage testing exception). Source: Idaho Falls City Code Title 7, Chapter 11; 2018 International Property Maintenance Code (IPMC), adopted per Idaho Falls City Code § 7-2-1. Source: Idaho Falls City Code Title 7, Chapter 2; 2018 International Fire Code (IFC), adopted per Idaho Falls City Code Title 7, Chapter 10 (referenced in Title 7 table of contents; administered by the Idaho Falls Fire Department). Source: Idaho Falls City Code Title 7, Chapter 10; 2018 International Existing Building Code (IEBC), adopted per Idaho Falls City Code Title 7, Chapter 12. Source: Idaho Falls Municipal Code Online, Title 7 Chapter 12; Idaho Falls City Code Title 11, Comprehensive Zoning, governs land-use, setback, fence-height, and accessory dwelling unit (ADU) standards enforced in conjunction with Building Division permitting. Source: Idaho Falls City Code Title 11. Local amendments apply — see the Idaho Falls overview page for the full list.

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.