How Boise Handles Accessory Structures: A Practical Guide

Boise maintains 188 local ordinances across all categories, and 9 of those deal specifically with accessory structures. Here is a breakdown of what the city actually requires, what is prohibited, and where Boise falls on the strict-to-permissive spectrum compared to other cities.

Tiny Homes

Boise recognizes tiny homes on foundations as ADUs under Idaho Code Section 67-6511A, typically capped at 900 sq ft. Tiny homes on wheels (RVs) are not permitted as permanent dwellings except in licensed RV parks.

Key details: Foundation Tiny: Permitted as ADU. Size Cap: 900 sq ft as ADU. THOW: RV park only. Appendix Q: IRC under 400 sq ft. State Law: §67-6511A applies.

Contact your local code enforcement office for specific penalty information.

Shed Rules

Sheds 200 sq ft or smaller in Boise do not require a building permit but must meet zoning setback rules (typically 3 ft side/rear). Larger structures require a permit and must comply with lot coverage limits.

Key details: Permit Exempt: 200 sq ft or less. Setback: 3 ft side/rear. Height: 15 ft at setback. Rear Coverage: 30% max. Electrical: Triggers permit.

Contact your local code enforcement office for specific penalty information.

Boise is more permissive than most cities when it comes to shed rules. That said, there are still limits.

Garage Conversions

Converting a garage to living space in Boise requires a building permit and full code compliance including egress, insulation, smoke alarms, and parking replacement. Garage conversions often qualify as ADUs under Idaho Code Section 67-6511A.

Key details: Permit: Always required. Parking: Must replace on lot. Ceiling: 7 ft minimum. ADU Option: §67-6511A if kitchen added. Historic: HPC review.

Unpermitted conversion: stop-work, retroactive permit fees, up to $1,000 civil penalty, and possible forced restoration if code cannot be met.

ADU Rules

Boise allows one ADU (attached or detached) on every single-family lot. Idaho Code Section 67-6511A (2023) limits cities from banning ADUs in single-family zones. Boise permits ADUs up to 900 sq ft with streamlined review.

Key details: State Law: Idaho Code §67-6511A. Max Size: 900 sq ft or 10% lot. Setback: 4 ft side/rear detached. Parking: Encouraged not required. STR Use: Allowed with registration.

Contact your local code enforcement office for specific penalty information.

Boise is more permissive than most cities when it comes to adu rules. That said, there are still limits.

Carport Rules

Under Boise City Code Title 11 (Development Code), Section 11-06-07, a carport is an accessory structure, defined as a structure open on at least two sides used to house motor vehicles of the occupants. In residential zones, garage and carport openings facing a side street must sit at least 20 feet from the side-street lot line, and detached accessory structures cannot encroach into required front or street-side yards.

Key details: Code: Title 11, Sec 11-06-07. Carport Definition: Open on >=2 sides, vehicle use. Side-Street Opening: >=20 ft from lot line. Front Yard: Not allowed without CUP. Small-Structure Threshold: <120 sq ft, <7 ft tall.

Building a carport in a required front or street-side yard, placing the opening less than 20 feet from a side-street lot line, or constructing an accessory structure that exceeds the dimensional standards of the underlying zone violates Boise City Code Title 11, Section 11-06-07. Unpermitted construction can result in stop-work orders and code-enforcement action through Planning & Development Services.

ADU Permits

Boise permits Accessory Dwelling Units by right on every single-family lot under the modernized Zoning Code Title 11 (effective December 2023). Idaho Code §67-6511A (enacted 2023) prohibits cities from banning ADUs in single-family residential zones. Boise allows ADUs up to 900 sq ft (or up to 10 percent of lot area) with streamlined administrative review through Planning and Development Services.

Key details: State Law: Idaho Code §67-6511A. Code Authority: Boise Zoning Title 11 (Dec 2023). Max Size: 900 sq ft or 10% of lot. By-Right Zones: R-1A through R-3. Detached Setbacks: 4 ft side / 4 ft rear.

Unpermitted ADU construction: PDS stop-work order, fines under Boise City Code, mandatory exposure of concealed work, and possible removal or full code-compliant retrofit. Building Code Board of Appeals may review enforcement matters. HPC violations in historic districts can require removal at owner expense.

If you are coming from a city with tighter rules, you will find Boise gives residents more flexibility on adu permits.

ADU Rental Restrictions

Boise allows ADUs to be rented long-term without restriction and short-term with STR registration through the City Clerk. Idaho preempts municipal rent control and source-of-income discrimination protections. Idaho Code §55-208 (2017) prohibits cities from banning short-term rentals outright. Boise STR rules limit licensing requirements rather than prohibiting use.

Key details: Long-Term Rental: Unrestricted. STR Registration: Required (City Clerk). STR Preemption: Idaho Code §55-115. Rent Control: Preempted (§55-307). Lodging Tax: 8% state (6% + 2%).

Operating an unregistered STR: Notice of Violation from City Clerk, fines under Boise City Code, and possible listing-removal cooperation requests to Airbnb/Vrbo. Failure to remit state lodging tax: Idaho State Tax Commission collection. Long-term rental disputes: tenant remedies through Idaho District Court small claims division or magistrate court under the Idaho Residential Landlord and Tenant Act.

Boise is more permissive than most cities when it comes to adu rental restrictions. That said, there are still limits.

ADU Owner Occupancy

Boise does not require owner-occupancy for ADU properties. Idaho Code §67-6511A (2023) prohibits cities from imposing owner-occupancy mandates that would make ADU construction impractical, placing Idaho among the most ADU-permissive states. Property owners may build an ADU on rental property, rent both units to separate tenants, or sell with the ADU intact. HOA covenants may still impose private restrictions.

Key details: City Rule: No owner-occupancy required. State Preemption: Idaho Code §67-6511A. Investor Ownership: Allowed. HOA Authority: Idaho Code Title 55. Common HOA Rules: Harris Ranch, Hidden Springs.

No city enforcement of owner-occupancy. HOA/condo violations result in declaration-based fines, typically $50-$500 per violation, with lien rights for unpaid assessments under Idaho Code Title 45. Civil litigation in Idaho District Court is available for declaration enforcement. State preemption under §67-6511A applies to local government rules; private covenants are governed separately under Idaho Code Title 55.

The rules around adu owner occupancy in Boise lean permissive, but that does not mean anything goes.

ADU Impact Fees

Boise charges impact fees on new dwelling units including ADUs under the authority of the Idaho Development Impact Fee Act (Idaho Code §67-8201 et seq.). Police, fire, and parks impact fees apply; Idaho law strictly limits the categories and requires rational nexus and proportional cost recovery. Building permit fees and water/sewer connection fees through Boise Public Works also apply.

Key details: State Authority: Idaho Code §67-8201 et seq.. Fee Categories: Police, fire, parks, transp. ADU Typical Rate: ~40-50% of single-family. School Fees: Not authorized in Idaho. Utility Connection: Only if new service.

Failure to pay impact fees blocks building permit issuance and certificate of occupancy under Idaho Code §67-8210. Building without permits to avoid fees: PDS stop-work order, double permit fees on after-the-fact applications, and mandatory exposure of concealed work. Misrepresentation of construction valuation on permit applications: civil and possibly criminal liability under Idaho Code.

The Bottom Line

Compared to many U.S. cities, Boise gives residents more room on accessory structures. 5 of the 9 rules here are rated permissive. But permissive does not mean unregulated. There are still requirements, and the city does enforce them when violations are reported.

All of the above reflects Boise's municipal code as of our last review. If you need specifics on fines, exemptions, or filing requirements, the detailed ordinance pages linked above have the full breakdown.