Can I Build ADU in Boise, ID? (2026)
Find out if you can build a adu in Boise, ID. Rules, permit requirements, costs, and next steps.
Yes, ADUs are allowed in Boise, ID. California state law ensures by-right approval.
An Accessory Dwelling Unit (ADU) is a secondary housing unit on a residential lot — also called a granny flat, in-law suite, or backyard cottage. In Boise, ID, ADUs are permitted by right under state law, making them one of the most accessible ways to add housing on your property. ADUs can be detached, attached to the main home, or created by converting an existing garage or accessory structure.
ADU Rules in Boise
ADU Rules in Boise: Detached ADU max size: 1000 sq ft. Attached ADU max size: No greater than 50% of primary dwelling floor area. Setbacks: 5 ft side, 10 ft rear. Owner-occupancy: No owner-occupancy requirement for ADUs in Boise. Property owner does not need to reside on site..
Costs & Fees
ADU permits in Boise: Total estimated permit cost: $1,500-$6,000 total permit fees for typical ADU. Contact the Boise Planning and Development Services — Building Division for current fee schedule.
Timeline
Boise Planning and Development Services processes building permits. Standard ADU permit: 4-8 weeks plan review. Construction typically 3-9 months.
Next Steps
Next steps for building an ADU in Boise: 1. Review full ADU rules including size limits, setbacks, and parking. 2. Apply for an ADU permit through the Boise Planning and Development Services — Building Division at https://www.cityofboise.org/departments/planning-and-development-services/building/permits/. 3. Hire a licensed contractor familiar with ID ADU requirements.
Boise Planning and Development Services — Building Division
Phone: (208) 384-3830
Website: https://www.cityofboise.org/departments/planning-and-development-services/
Online Permits: https://www.cityofboise.org/departments/planning-and-development-services/building/permits/
Frequently Asked Questions
Can I build an ADU in Boise?
Yes. Boise allows ADUs (accessory dwelling units) through its local zoning code (City Code Title 11). You can build a detached or attached ADU on most residential lots. Idaho does not have statewide ADU preemption, but Boise has adopted permissive local ADU allowances. Detached ADUs are limited to 1,000 sqft. No owner-occupancy requirement applies. Permits are processed by Boise Planning and Development Services.
Does Boise require a permit for short-term rentals?
Yes. Boise requires a Short-Term Rental License ($125/year) for all Airbnb-style rentals. An annual fire safety inspection is also required. The license number must be displayed on all listing platforms. Airbnb and VRBO collect and remit applicable Idaho state sales tax and local lodging taxes on behalf of hosts.
What are the setbacks in an R-1C zone in Boise?
In an R-1C zone in Boise (standard single-family residential), the setbacks are: 20 ft front, 5 ft each side, and 20 ft rear. ADUs must maintain 5 ft side and 10 ft rear setbacks. Always verify specific parcel setbacks with Boise Planning and Development Services.
Are solar panels required on new homes in Boise?
No. Idaho does not have a solar mandate for residential construction. Solar is voluntary in Boise. Idaho Power serves the Boise area and offers net metering through their Solar PV Program. HOAs have limited ability to prohibit solar installations under Idaho Code Section 55-115.
What makes Boise zoning unique?
Boise is one of the fastest-growing cities in the US and has updated its zoning code to address rapid growth and housing demand. The city has hillside development constraints through the Hillside and Foothill Development Ordinance for properties in the foothills areas. Boise is also notable for its Greenbelt trail system along the Boise River, which creates open space requirements near the river.
Source: Boise Planning and Development Services — Building Division — Building Regulations. Last verified April 5, 2026. View source