Accessory Dwelling Unit (ADU) Permit in Boise, Idaho
Required for construction of a new accessory dwelling unit on a residential property in Boise, including detached cottages, attached additions, and internal conversions. Boise offers a Pre-Approved ADU program (permit type 402-B) with pre-reviewed plan sets to expedite permitting.
Verified 2026-06-29 · Source
When you need this permit
- Property must be zoned to allow an ADU under Boise Zoning Code
- Pre-Approved ADU program (402-B) allows use of Boise-reviewed plan sets — fastest path
- Standard ADU uses the New Residential (402) or Additions/Alterations (406) permit depending on type
- Submit Pre-Approved ADU Submittal Checklist for 402-B program
Required documents
- Req
Pre-Approved ADU Submittal Checklist
Required checklist for the 402-B Pre-Approved ADU program; available from the 402-B permit page
- Opt
Construction Drawings
Full construction drawings for custom ADU designs; not required if using pre-approved plan set
Fee schedule
| Fee type | Amount | Notes |
|---|---|---|
| ADU Building Permit — valuation-based per Table 1-A | Same valuation-based schedule as new residential construction (Table 1-A); residential plan review is 20% of permit fee | Boise Building Code Fee Schedule (Oct 2023) |
Review timeline
~9–84 business days
Typical estimate — confirm current times with the Boise building department
Inspection process
- 1
Foundation
Footings and foundation before concrete pour
- 2
Framing
Structural framing, egress windows, fire separation
- 3
MEP Rough-In
Mechanical, electrical, plumbing rough-ins before walls closed
- 4
Final
All work complete, smoke/CO detectors, address posted, ready for occupancy
Tips
- Boise's Pre-Approved ADU program (402-B) offers pre-reviewed plan sets that can significantly reduce plan review time.
- Confirm ADU zoning eligibility through the Boise Zoning Code before applying.
- Trade sub-permits (electrical, plumbing, mechanical) are required separately for ADU construction.
Frequently asked questions
- Does Boise have a pre-approved ADU program?
- Yes. Boise offers a Pre-Approved ADU program (permit type 402-B) with plan sets that have already been reviewed by the city. Using a pre-approved plan can reduce plan review time. Apply at permits.cityofboise.org.
Sources & verification
Key facts verified against official sources. Last reviewed 2026-06-29.
- Boise Planning and Development Services — Building Division — official building department
- 402-B — Pre-Approved ADU | City of Boise
- Boise City Building Code Fee Schedule (Oct 2023)
Fees, timelines, and adopted codes are researched from each jurisdiction's published records — see how we verify. Requirements change and vary by project, so always confirm the current details with the Boise building department before you submit. PermitBase is an independent reference and is not affiliated with any government agency.
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