Building permits, zoning and septic rules in Twin Falls County, Idaho

Unincorporated Twin Falls County requires a building permit when a structure is erected, constructed, remodeled, enlarged, altered, repaired, moved, removed, converted or demolished¹. The county specifically requires permits for interior remodeling, including nonstructural-wall work and changes to window or door sizes, and directs applicants to ask the Building Department about limited exemptions¹. A residential accessory building under 200 square feet can qualify for an exemption¹. Twin Falls County has adopted the 2018 building, residential, energy, mechanical, fuel-gas, existing-building and fire codes with Idaho amendments, plus the 2018 Idaho Manufactured Home Installation Standards⁸. Electrical, plumbing and HVAC work requires separate permits⁹. State plumbing, electrical, gas, mechanical, fireplace, and firewall or sprinkler rough-ins must be signed off before the county framing inspection; corresponding finals must precede the county final building inspection¹⁰. A final inspection and an occupancy permit are required before a new or remodeled structure is used, and occupancy approval may be withheld while a required inspection is incomplete¹.

Inside Twin Falls, Kimberly, Buhl and Hansen city limits, the city handles building permits^11,12,13,14. South Central Public Health District remains the district administering state septic rules in Twin Falls County; Hansen also requires a city private-sewage permit and inspection^15,16,17.

The Twin Falls County Building Department reviews plans, issues building permits and handles building and mechanical inspections¹⁸. Reach the department at 630 Addison Ave. West, Ste 1101, Twin Falls, ID 83301, or (208) 933-9279; request building inspections at (208) 735-4429 and mechanical inspections at (208) 735-4432¹⁸. Complete residential submissions are reviewed in the order received, with plan review usually estimated at no more than 7 business days¹. A permit expires 180 days after issuance or the last inspection, so keep inspections current¹. Give the permit number, property address, contact name and phone number, and inspection type when requesting an inspection; requests after 7:00 a.m. move to the next working day¹⁰. The county links a Building & Zoning Fee Schedule from its Community Development Services page, and the cited schedule is the 2025 edition, so confirm the current fee with the Building Department¹⁸. For parcel zoning and land-use applications, contact the Planning & Zoning Department at 630 Addison Ave. West, Suite 1100, Twin Falls, Idaho 83301, or 208-734-9490¹⁸.

Twin Falls County zoning covers unincorporated land, including areas of city impact where city regulations may be adopted by reference². Inside city limits, Twin Falls, Kimberly, Buhl, Filer, Hansen and Hollister set their own zoning^{19,20,21,22,23,24}. South Central Public Health District administers state septic rules for Twin Falls County, while Hansen additionally requires city approval of private sewage systems^15,16,17.

For unincorporated parcels, ask Planning & Zoning to identify the controlling county or area-of-impact code and mapped district^2,3,18. Rural Residential lots generally need 1 acre with individual water and sewage, or 9,000 square feet with public or private sewer and water². RR front and rear yards are generally 30 feet and interior side yards 7 feet, with larger yards for taller buildings². Canyon Rim Overlay parcels have separate setback and height controls². We could not confirm a general minimum size for site-built homes; ask Planning & Zoning about the parcel's district¹⁸.

Septic permits in Twin Falls County are not issued by the county: the South Central Public Health District administers Idaho's statewide subsurface sewage disposal rules for the county^2,16. The county zoning code itself bars anyone from installing or using a sewage-disposal facility until the district approves it, and where a district-approved public sewer is reasonably available the lot must connect to it². Reach the district's Twin Falls main office at 1020 Washington Street North, Twin Falls, ID 83301, phone (208) 737-5900, or email septic questions to septic@phd5.id.gov¹⁵. Use the district’s septic records portal to look up existing systems; septic permits were not required before 1971, so older systems may lack records²⁵. South Central Public Health District inspects individual septic installations; when inspection preparation is required, give at least 48 hours’ advance notice, excluding weekends and holidays²⁶. About 8% of Twin Falls County soils are rated ‘not limited’ for conventional septic drain fields; that does not rule out septic elsewhere, but makes a site evaluation essential and an engineered system possible²⁷.

An occupied recreational vehicle may remain on an unincorporated Twin Falls County lot for no more than 90 days in a calendar year². A tiny home is treated as a mobile or manufactured home only if it qualifies as one; in unincorporated Twin Falls County that placement needs an approved application to the County Building Department, a parcel that meets the zone's minimum lot size, and the single-family area and yard standards⁴. The unit must be at least 12 feet wide and 1,000 square feet, with a HUD label or the specified Idaho compliance certificate for homes manufactured before June 1976⁴. We could not confirm a rule for other tiny homes, so ask Planning & Zoning to classify the unit before you buy¹⁸. A manufactured-home park requires a conditional use permit and health-district approval of its sanitation and layout². Every manufactured-home installation must be inspected and approved by the state or local authority before occupancy²⁸.

1. Ask Planning & Zoning to identify the controlling county or area-of-impact code, mapped district, lot dimensions and overlays before design begins^2,3,18.
2. Determine whether the site lies in a Special Flood Hazard Area; county permits are required before construction or development there².
3. Confirm access with the highway district serving the property and show the driveway or access road on the site plan².
4. Contact South Central Public Health District for the septic permit, and obtain an Idaho well-drilling permit if the project needs a well deeper than 18 feet^2,7.
5. Submit complete plans and supporting documents to the Building Department; complete residential review is usually estimated at no more than 7 business days¹.
6. Obtain separate electrical, plumbing and HVAC permits, complete state trade rough-ins before county framing inspection and trade finals before county final inspection, and secure occupancy approval before using the structure^2,9,10.

About 8% of Twin Falls County soils rate ‘not limited’ for conventional septic drain fields, so resolve parcel-specific septic feasibility before buying²⁷. Twin Falls County publishes separate preliminary-plat, final-plat, administrative land-division, conditional-use land-division and lot-line-adjustment applications²⁹. A division into more than 3 parts for transfer or development is generally a regulated subdivision, subject to listed exceptions². A subdivision or planned development within one-half mile of a municipality must connect to municipal water and sewer when the municipality allows it². Check the mapped zoning district, applicable area-of-impact code, overlays and flood status before closing^2,3. A driveway must follow the serving highway district's rules, while state-highway access also needs an Idaho Transportation Department encroachment permit^2,30.