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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 2026-07-16 · 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

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Fee schedule

ADU Building Permit — valuation-based per Table 1-A
Assessed on project valuation per Boise's Building Code Fee Schedule, Table No. Show full citationAssessed on project valuation per Boise's Building Code Fee Schedule, Table No. 1-A (Oct 2023, item 9 for the 20% residential plan review add-on), cited. Confirmed the schedule has no separate ADU-specific fee line — the 402-B Pre-Approved ADU program page (permits.cityofboise.org checklist/apply-online only) and the fee schedule PDF both show new/converted ADUs are billed as standard residential construction under Table 1-A, same as the 402 New Residential Construction permit.
Same valuation-based schedule as new residential construction (Table 1-A): $26.37 + $2.95/$100 (up to $2,000); $70.76 + $12.71/$1,000 ($2,001–$25,000); $362.80 + $9.30/$1,000 ($25,001–$50,000); $595.30 + $6.35/$1,000 ($50,001–$100,000); $913.09 + $5.17/$1,000 ($100,001+)
Residential Plan Review (1- and 2-family dwellings, townhouses, and accessory structures)Per Boise Building Code Fee Schedule item 9
20% of the building permit fee

Review timeline

Plan reviewTypical estimate — confirm current times with the Boise building department
~9–84 business days

How long did your Accessory Dwelling Unit (ADU) Permit permit actually take in Boise?

Anonymous — one question, no email. Answers are combined and only shown once at least 5 people have reported.

Inspection process

  1. 1

    Foundation

    Footings and foundation before concrete pour

  2. 2

    Framing

    Structural framing, egress windows, fire separation

  3. 3

    MEP Rough-In

    Mechanical, electrical, plumbing rough-ins before walls closed

  4. 4

    Final

    All work complete, smoke/CO detectors, address posted, ready for occupancy

See the full Boise inspection guide — scheduling & re-inspection fees →

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

Boise requires an accessory dwelling unit (adu) permit for: 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. If your project isn't listed, confirm with Boise Planning and Development Services — Building Division at (208) 608-7070 before starting work.

In Boise, the published ADU Building Permit — valuation-based per Table 1-A is: Same valuation-based schedule as new residential construction (Table 1-A): $26.37 + $2.95/$100 (up to $2,000); $70.76 + $12.71/$1,000 ($2,001–$25,000); $362.80 + $9.30/$1,000 ($25,001–$50,000); $595.30 + $6.35/$1,000 ($50,001–$100,000); $913.09 + $5.17/$1,000 ($100,001+). Additional published fees: Residential Plan Review (1- and 2-family dwellings, townhouses, and accessory structures) — 20% of the building permit fee. These are the jurisdiction's own published figures — see the fee schedule table and source citations on this page.

Plan review for an accessory dwelling unit (adu) permit in Boise typically runs 9–84 business days. This is an estimate, not a published figure — confirm current review times with Boise Planning and Development Services — Building Division at (208) 608-7070.

You'll need: Pre-Approved ADU Submittal Checklist. Depending on your project, Boise may also ask for: Construction Drawings. See the required-documents checklist on this page for details on each.

Boise requires 4 inspection(s) for an accessory dwelling unit (adu) permit, in order: Foundation, Framing, MEP Rough-In, Final. Schedule each through Boise Planning and Development Services — Building Division ((208) 608-7070).

Apply through Boise Planning and Development Services — Building Division at 150 N Capitol Blvd, Boise, ID 83702. Phone: (208) 608-7070, email: permits@cityofboise.org. Office hours: Mon–Fri 8:00 AM – 5:00 PM (closed holidays). Official information: https://www.cityofboise.org/departments/planning-and-development-services/building/.

Boise, Idaho has adopted: 2018 International Building Code (IBC) — with Appendices H (Signs) and J (Grading); Mass Timber provisions only of the 2021 IBC; 2018 International Existing Building Code (IEBC); 2018 International Residential Code (IRC), Parts I–IV and IX — with Appendices Q (Tiny Houses) and S (Strawbale Construction); 2018 International Energy Conservation Code (IECC); 2017 Idaho State Plumbing Code (based on the 2015 Uniform Plumbing Code, including Chapter 13 – Medical Gas); 2023 National Electrical Code (NEC) — effective April 26, 2024; 2018 International Fire Code (IFC) — with Appendices B, C, D, F and L; 2019 NFPA 13; 2019 NFPA 72; 2018 International Mechanical Code (IMC) — commercial and residential projects with 3+ units; 2018 International Fuel Gas Code (IFGC) — commercial and residential projects with 3+ units; 2018 IRC Parts V and VI — single- and two-family residential mechanical and fuel gas. Local amendments apply — see the Boise overview page for the full list.

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

Verified against official sources. Last reviewed 2026-07-16.

Fee schedules

Department & other records

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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Accessory Dwelling Unit (ADU) Permit in other cities

Idaho Falls, IdahoMeridian, IdahoNampa, IdahoAlbuquerque, New MexicoArvada, ColoradoAurora, ColoradoBoulder, ColoradoBountiful, Utah

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