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Accessory Dwelling Unit (ADU) Permit in Helena, Montana

Required for construction of an Accessory Dwelling Unit on a residential parcel within Helena city limits. Helena City Code Title 11 (Zoning) formally defines and permits ADUs by right in nearly all residential and mixed-use zoning districts; construction itself follows the standard City of Helena residential building permit process under the 2021 IRC/IBC.

Verified 2026-07-02 · Source

When you need this permit

  • ADU defined at Helena City Code 11-2-4 as 'a self-contained living unit on the same parcel as a single-dwelling unit of greater square footage that includes its own cooking, sleeping, and sanitation facilities and complies with or is otherwise exempt from any applicable building code, fire code, and public health and safety regulations'
  • Per the Title 11 Land Use Table (City Code 11-2-3), 'Residence, accessory dwelling unit (ADU)' is listed as Permitted (P) by right in the R-R, R-1, R-2, R-3, R-4, R-O, B-1, B-2, B-3, DT, and TR zoning districts, subject to the standards of City Code Section 11-2-5J (Not Permitted in CLM, M-I, and Airport districts)
  • Construction must comply with the same 2021 IRC/IBC standards, climatic design criteria (Table R301.2), and permit application process as other residential building permits
  • Setback (City Code 11-4-2) and lot coverage (City Code 11-4-1) requirements apply to the ADU structure

Required documents

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Fee schedule

Building Permit Fee — valuation-based (same Ordinance 3134 table as new construction)No separate ADU-specific fee schedule is published by the City of Helena; an ADU is billed as new residential construction under the standard valuation-based table
Per Ordinance 3134 Appendix A valuation table, based on the ADU's construction valuation
Plan Review (Plan Check) FeePer the City's standard building permit fee structure
65% of the Building Permit Fee

Review timeline

Plan reviewTypical estimate — confirm current times with the Helena building department
~10–15 business days

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

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

Inspection process

  1. 1

    Foundation

    Before concrete pour

  2. 2

    Framing

    After framing complete, before insulation or wall cover

  3. 3

    MEP Rough-In

    Electrical, plumbing, mechanical rough-in before walls closed (separate trade permits required)

  4. 4

    Final

    Approved final inspection required before occupancy

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

Tips

  • Helena's zoning code (Title 11) explicitly defines and permits ADUs by right in nearly every residential and mixed-use zoning district — confirm your specific parcel's zone using the City of Helena Zoning Map before assuming by-right status.
  • There is no separate ADU building-permit fee schedule; budget using the same Ordinance 3134 valuation-based table as a standalone new home.
  • Setback and lot coverage compliance (City Code 11-4-1, 11-4-2) is checked independently of the building code review — confirm with the Planning Division early in design.

Frequently asked questions

Helena requires an accessory dwelling unit (adu) permit for: ADU defined at Helena City Code 11-2-4 as 'a self-contained living unit on the same parcel as a single-dwelling unit of greater square footage that includes its own cooking, sleeping, and sanitation facilities and complies with or is otherwise exempt from any applicable building code, fire code, and public health and safety regulations'; Per the Title 11 Land Use Table (City Code 11-2-3), 'Residence, accessory dwelling unit (ADU)' is listed as Permitted (P) by right in the R-R, R-1, R-2, R-3, R-4, R-O, B-1, B-2, B-3, DT, and TR zoning districts, subject to the standards of City Code Section 11-2-5J (Not Permitted in CLM, M-I, and Airport districts); Construction must comply with the same 2021 IRC/IBC standards, climatic design criteria (Table R301.2), and permit application process as other residential building permits; Setback (City Code 11-4-2) and lot coverage (City Code 11-4-1) requirements apply to the ADU structure. If your project isn't listed, confirm with City of Helena — Community Development Department, Building Division at (406) 447-8438 before starting work.

In Helena, the published Building Permit Fee — valuation-based (same Ordinance 3134 table as new construction) is: Per Ordinance 3134 Appendix A valuation table, based on the ADU's construction valuation. Additional published fees: Plan Review (Plan Check) Fee — 65% 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 Helena typically runs 10–15 business days. This is an estimate, not a published figure — confirm current review times with City of Helena — Community Development Department, Building Division at (406) 447-8438.

You'll need: Permit Application (City of Helena Building Division); Residential Plan Submittal Requirements; Site Plan. See the required-documents checklist on this page for details on each.

Helena requires 4 inspection(s) for an accessory dwelling unit (adu) permit, in order: Foundation, Framing, MEP Rough-In, Final. Schedule each through City of Helena — Community Development Department, Building Division ((406) 447-8438).

Apply through City of Helena — Community Development Department, Building Division at 316 N. Park Avenue, Room 435, Helena, MT 59623. Phone: (406) 447-8438, email: CityBuilding@helenamt.gov. Office hours: City County Building, 316 N Park Ave, Helena, MT 59623; applications and permits also processed online via Civic Access (helenamt.gov/business/civic-access/). Official information: https://www.helenamt.gov/Departments/Community-Development/Building.

Helena, Montana has adopted: 2021 International Building Code (IBC) — Montana statewide adoption, effective June 11, 2022; enforced by the City of Helena within city limits under its DLI-certified Building Code Enforcement Program; 2021 International Residential Code (IRC), for One- and Two-Family Dwellings — Montana statewide adoption, effective June 11, 2022; City of Helena Building Division is the local Authority Having Jurisdiction (AHJ) for one- and two-family dwellings under IRC Chapters 8 and 9, including roofing/re-roofing; 2021 International Existing Building Code (IEBC) — Montana statewide adoption, effective June 11, 2022; ICC A117.1-2017 (Accessibility) — Montana statewide adoption, effective June 11, 2022; 2021 Uniform Plumbing Code (UPC) — Montana statewide adoption, effective June 11, 2022; City of Helena is certified to enforce plumbing (P) within city limits; 2021 International Mechanical Code (IMC) — Montana statewide adoption, effective June 11, 2022; City of Helena is certified to enforce mechanical (M) within city limits; 2021 International Fuel Gas Code (IFGC) — Montana statewide adoption, effective June 11, 2022; 2020 National Electrical Code (NEC) — Montana statewide adoption, effective June 11, 2022 (Technical Advisory NEC_TIA-23-3_210.8 issued August 12, 2022); City of Helena is certified to enforce electrical (E) within city limits; 2021 International Energy Conservation Code (IECC) — Montana statewide adoption, effective June 11, 2022; 2021 International Swimming Pool and Spa Code (ISPSC) — Montana statewide adoption, effective June 11, 2022; 2021 Wildland Urban Interface (WUI) Code — Montana statewide adoption, effective June 11, 2022 (Helena is NOT listed as WUI-certified; WUI enforcement in Helena's jurisdiction area is not confirmed — see notes); Statewide code administered by the Montana Department of Labor & Industry (DLI), Business Standards Division, Building Codes Program (formerly/also referenced as the Building Codes Bureau) — Mont. Code Ann. Title 50, Chapter 60, Parts 1-4. Local amendments apply — see the Helena overview page for the full list.

Yes. Helena City Code 11-2-4 defines an Accessory Dwelling Unit, and the Title 11 Land Use Table lists ADUs as Permitted (P) by right in nearly all residential and mixed-use zoning districts (R-R, R-1 through R-4, R-O, B-1 through B-3, DT, and TR), subject to City Code Section 11-2-5J standards.

Sources & verification

Verified against official sources. Last reviewed 2026-07-02.

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 Helena 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

Bozeman, MontanaGreat Falls, MontanaKalispell, MontanaMissoula, MontanaUnincorporated Yellowstone County, MontanaAlbuquerque, New MexicoArvada, ColoradoAurora, Colorado

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