Twin Falls County, ID Building Setbacks & Zoning: Lot Coverage Limits (2026)
Key Facts
- Governing section
- County Code § 8-12-1(B)(7)
- Max combined coverage
- 35% of the lot
- Excluded from coverage
- Underground shelter area, § 8-12-1(B)(5)
- Ag Range Preservation cap
- 3,200 to 5,000 sq ft accessory
- Over-cap remedy
- Requires conditional use permit
- Penalty
- Up to $300 fine, 6 months jail (§1-4-1)
Summary
In agricultural and residential zones of unincorporated Twin Falls County, the combined footprint of a house and its accessory buildings cannot exceed thirty-five percent of the lot. County Code section 8-12-1(B)(7) sets that cap, and subsection (B)(5) excludes any underground shelter's area from the coverage calculation.
8-12-1: SPECIAL PROVISIONS: ... B. Accessory Building In Agricultural And Residential Zones: ... 5. Acceptance: Commercial variations may request planning and zoning commission acceptance. The area of underground shelters shall not be computed in maximum coverage requirements. ... 7. Coverage: Combined coverage of the property by the primary and accessory buildings shall not exceed thirty five percent (35%). ... 8. Size Limitations: a. Agricultural Range Preservation Zone: On parcels containing less than applicable zone acreage requirements, the building square footage is restricted to a maximum size of three thousand two hundred (3,200) square feet. On parcels meeting zoning requirements, the building square footage is restricted to a maximum size of five thousand (5,000) square feet. A conditional use permit shall be required for any construction proposed over the maximum square footage.
Full Breakdown
Title 8's special provisions chapter regulates accessory buildings and uses on the same lot as a home in the county's agricultural and residential zones. Section 8-12-1(B) sets a series of standards for those accessory structures, including height, placement and separation rules, and subsection (B)(7), titled Coverage, states plainly that combined coverage of the property by the primary and accessory buildings shall not exceed thirty five percent (35%). That is a combined cap, not a separate allowance for the house and then again for a shop or barn: the primary dwelling and every accessory building or enclosure on the lot are added together against the same 35 percent ceiling.
Subsection (B)(5) carves out one exception: the area of underground shelters shall not be computed in maximum coverage requirements, so a fallout shelter or similar underground structure does not count against the cap even though it counts toward size limits elsewhere. Those size limits appear in subsection (B)(8): in the Agricultural Range Preservation Zone, an accessory building is capped at 3,200 square feet on a parcel smaller than the applicable zone acreage requirement, rising to 5,000 square feet on a parcel that meets the acreage requirement, and any construction proposed above that ceiling needs a conditional use permit.
Coverage and size act as two separate checks on the same accessory structure: a building can be within its square-footage cap and still be denied if it pushes the lot's combined coverage past 35 percent.
Violations & Fines
Building beyond the 35 percent combined coverage cap, or beyond the accessory-building size limits in section 8-12-1(B)(8) without the required conditional use permit, is a zoning violation. It is enforced under the county's general penalty, section 1-4-1, a misdemeanor punishable by up to a $300 fine and up to six months in jail, with the Board of County Commissioners or Zoning Administrator able to require the excess structure removed or brought into compliance.
Frequently Asked Questions
What is the maximum lot coverage allowed in unincorporated Twin Falls County?
Does an underground shelter count toward the 35 percent lot coverage cap?
Are accessory buildings capped in square footage separately from the coverage percentage?
Sources & Official References
Other rules in Twin Falls County
Compare Twin Falls County to another location·View the Idaho building setbacks & zoning overview
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