Building permits, zoning and septic rules in Boise County, Idaho

Unincorporated Boise County requires a building permit for new construction, and the site plan must show Wildland-Urban Interface defensible space and setbacks¹. Inside Horseshoe Bend and Idaho City, the city issues building permits^4,5. Septic permitting stays with Central District Health in both cities⁶. Idaho has adopted the 2018 International Building Code and the Idaho Residential Code (2020 Edition), based on parts of the 2018 International Residential Code with Idaho amendments¹². A pre-application meeting with the Planning & Zoning Administrator is required before any land-use or development application². Boise County requires building inspections; its fee schedule bases most residential work on 6 inspections at $150 each, although some projects need more or fewer⁹. Electrical, plumbing and HVAC work require separate trade permits¹³.

Boise County Planning & Zoning is the building-permit and land-use contact for unincorporated land². Reach the office at 413 Main Street, PO Box 1300, Idaho City, ID 83631, phone 208-392-2293². The office is open Monday through Thursday, 8:00 am to 5:00 pm, and Friday 8:00 am to 1:00 pm; building-permit service is limited to 8:30 am through 4:00 pm². For inspections, call 208-781-8565 and allow 48 hours excluding weekends². Boise County publishes a $100 minimum building-permit fee and a $50 minimum plan-review fee; outside professional costs can also be charged, and review stops if a required supplemental payment remains unpaid⁹.

Unincorporated Boise County has a Unified Land Use Ordinance with zoning districts and setback standards administered by Planning & Zoning^2,3. Inside Horseshoe Bend, the city sets its own zoning; septic permitting remains with Central District Health^6,14. The county website lists Amended Unified Land Ordinance 2024-02; ask Planning & Zoning which edition governs your parcel². Before designing a home in unincorporated Boise County, confirm the parcel’s district, setbacks and Wildland-Urban Interface defensible-space requirements with Planning & Zoning^1,2.

Central District Health handles septic permits throughout Boise County and reviews land-development proposals for release of sanitary restrictions⁶. CDH’s Idaho City office is at 102 Centerville Rd, Idaho City, ID 83631, phone 208-327-7400; applications and inspection results are available through Accela^6,15. Installing, modifying, repairing or expanding an individual septic system generally requires an installation permit, with limited exceptions for certain piping or component repairs that do not expand the system¹⁶. CDH’s July 2026 fee schedule lists a new-system permit at $1,070, or $535 without a test hole or site visit⁶. Drainfield evaluations require test holes for every lot or parcel, with a CDH Environmental Health Specialist present; the owner or agent must arrange excavation equipment and attend the inspection⁷. Ask CDH whether an existing evaluation qualifies your project for the no-site-visit fee before arranging excavation^6,7. About 0.1% of county soils are rated not limited for conventional drain fields; septic may still be possible, but establish parcel-specific feasibility before buying¹⁰.

For unincorporated Boise County, Planning & Zoning publishes “Standards for Tiny Homes/RVs,” so do not assume rural land allows either use automatically². We could not confirm the operative occupancy limits; ask Planning & Zoning how the standards and the parcel's zoning district apply before buying or moving in an RV or tiny home². A manufactured home is a separate category: every installation must be inspected and approved by the state or the authority having jurisdiction before occupancy, while the state installation permit and tag apply only to new homes where no approved local building program operates¹¹.

1. Schedule the required pre-application meeting with Boise County Planning & Zoning for unincorporated land².
2. Confirm the zoning district, setbacks and Wildland-Urban Interface defensible-space requirements^1,2.
3. Apply to Central District Health through its Accela portal, submit the required plans and fees, and arrange excavation equipment and attend the required witnessed test-hole inspection before counting on septic approval^6,7.
4. Obtain an Idaho Department of Water Resources drilling permit before drilling a well and use a licensed driller¹⁷.
5. Apply for the county building permit and separate electrical, plumbing or HVAC permits; budget for plan review and staged building inspections^1,9,13.
6. If the site is in a floodplain, secure the other necessary permits before the floodplain permit and do not begin work until that permit is issued¹⁸.
7. Obtain an Idaho Transportation Department encroachment permit for a driveway connecting to a state highway¹⁹.

About 73.6% of Boise County is federal land, so verify parcel boundaries and recorded access rather than assuming an adjoining road or trail conveys private access¹⁰. About 0.1% of county soils are rated not limited for conventional septic drain fields; that does not rule out septic, but warrants a site evaluation before closing¹⁰. Just 11.4% of Boise County is at a slope of 15% or less, while 67.3% is wooded; inspect the build pad, driveway grade and defensible-space burden in person¹⁰. A new well requires an IDWR drilling permit and a licensed well driller¹⁷. Boise County floodplain work cannot begin before the floodplain development permit is issued, and the county will not issue that permit until other necessary permits are obtained¹⁸. Typical home value is about $490,130, the effective property-tax rate is about 0.4%, and the median annual bill is about $1,571¹⁰. Boise County has about 8,517 residents at 4.5 people per square mile, and the nearest city of 100,000 or more is about 34 miles in a straight line from the county center¹⁰.