Residential Building Permit (New Construction / Addition) in Unincorporated Twin Falls County, Idaho

Unincorporated Twin Falls County requires a residential building permit (new construction / addition) for: Building permit required for new residential construction, additions, garages/carports, covered decks/patios, and any deck with a walking surface more than 30 inches above grade; Parcel number (obtained from the County Assessor's Office); Copy of the deed showing ownership, including legal description (obtained from the County Clerk's Office); Authorization Form signed by the property owner if the applicant is not the owner; Two (2) sets of plans drawn to 1/4 inch = 1'0" scale (or computer-generated plans at not less than 1/8 inch = 1'0"), submitted as a PDF for digital submittal; Site plan showing property lines, lot dimensions, survey corner stakes, easements, rights-of-way, well/septic locations, all existing structures, proposed structure with dimensions and setbacks, driveway, and surface drainage; Two (2) site plans stamped approved by the South Central Public Health District; Building plans: footing/foundation plan with reinforcement, floor plan, egress window/smoke/CO detector locations, floor framing, crawlspace venting, beam/header sizing, stair details, wall shear bracing, elevations (minimum 2), and a completed energy conservation certification (RESCheck or prescriptive); Highway District, Canal Company, and Fire District approval/comment letters; FEMA Elevation Certificate required before permit issuance if the parcel is within 100 feet of a major waterway (and again before final inspection); Architect/engineer-stamped plans required only if the building is more than two stories or of unusual design requiring professional structural assistance; Plan Review Fee (35% of the building permit fee, or $100, whichever is greater) is due at time of submittal and is non-refundable. If your project isn't listed, confirm with Twin Falls County Community Development Services — Building Department at 208-734-9490 before starting work.

Effective September 1, 2025, a non-refundable Plan Review Fee of 35% of the building permit fee (or $100, whichever is greater) is due at the time of plan submittal, in addition to the building permit fee itself (collected when the permit is issued). Source: Twin Falls County Community Development Services Fee Schedule, effective 9/1/2025.

The county's Residential Building Permit Information handout states the estimated time for a residential plan review is usually not more than seven business days, contingent on the submittal of complete plans, specifications, and all required supporting documents (South Central Public Health approval, Highway District/Canal Company/Fire District comment letters, etc.). Source: Twin Falls County Residential BP Information handout, twinfallscounty.org/building_department/applications/.

You'll need: Residential Building Permit Application (Updated 9/2025, fillable PDF); Building Applications Submittal Checklist (5/2024); South Central Public Health District Approval / Septic Permit. Depending on your project, Unincorporated Twin Falls County may also ask for: Residential BP Information Handout (Rev. 1/2014); Example Site Plan; Authorization Form. See the required-documents checklist on this page for details on each.

Unincorporated Twin Falls County requires 3 inspection(s) for a residential building permit (new construction / addition), in order: Footing / Foundation, Framing, Final. Schedule each through Twin Falls County Community Development Services — Building Department (208-734-9490).

Apply through Twin Falls County Community Development Services — Building Department at 630 Addison Avenue West, Suite 1100, Twin Falls, ID 83301. Phone: 208-734-9490. Office hours: Mon–Fri 8:00 AM – 5:00 PM (Building Department closed for lunch 12:30 PM – 1:30 PM). Official information: https://twinfallscounty.org/community-development-services/.

Unincorporated Twin Falls County, Idaho has adopted: 2018 International Building Code (IBC) with Idaho Amendments; 2018 International Residential Code (IRC) with Idaho Amendments; 2018 International Energy Conservation Code (IECC) with Idaho Amendments; 2018 International Mechanical Code (IMC) with Idaho Amendments; 2018 International Fuel Gas Code (IFGC) with Idaho Amendments; 2018 International Existing Building Code (IEBC) with Idaho Amendments; 2018 International Fire Code (IFC) with Idaho Amendments; 2018 Idaho Manufactured Home Installation Standards. Local amendments apply — see the Unincorporated Twin Falls County overview page for the full list.

No. Electrical and plumbing permits for unincorporated Twin Falls County are issued and inspected by the Idaho Division of Building Safety (state agency, formerly under DOPL), not the county. Call 1-800-955-3044 or visit dbs.idaho.gov. Mechanical/HVAC permits are the exception — Twin Falls County issues and inspects those directly under its own Mechanical Permit application and fee schedule. Source: Twin Falls County Residential BP Information handout; Twin Falls County HVAC Permit Application (2021, referenced in the 2025 fee schedule).