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MontanaSB 53269th Legislature, Regular Session (2025)SenateWALLET

Revise county zoning to allow accessory dwelling units

Sponsored By: Forrest Mandeville (Republican)

Became Law

Planning and DevelopmentCountiesEnvironmental ProtectionHousingLocal GovernmentRevenue, LocalRevenue, State

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Bill Overview

Analyzed Economic Effects

4 provisions identified: 1 benefits, 1 costs, 2 mixed.

Counties must allow one ADU per home

Counties with zoning must allow at least one accessory dwelling unit (ADU) by right on any lot with a single‑family home. An ADU can be attached, detached, or inside; attached or detached units are capped at 75% of the home’s floor area or 1,000 sq. ft., whichever is less. “By right” means no public hearing or special permit, only a site plan check. Counties cannot require extra parking, owner‑occupancy, matching exterior design, impact fees, costly street upgrades, or stricter height, setback, lot size, coverage, or frontage rules. They also cannot require restrictive covenants or ties between occupants; private covenants may still exist, but permits cannot depend on them. Counties must follow this state rule now, and can still enforce building, fire, and health codes.

One-time $250 ADU application fee

A county may charge a one‑time ADU application review fee up to $250 for each ADU. You also pay the usual building permit fees.

Faster ADU reviews through 2029

DEQ must finish sanitation review for an ADU within 15 days if the parcel already has public water and sewer with capacity. If you need a subdivision deviation only to add an ADU on such a parcel, you also get a 15‑day review. These expedited reviews apply through September 30, 2029.

Counties can regulate short-term rentals

This law does not stop counties from regulating short‑term rentals under state law. Local rules may still limit using an ADU for short‑term renting.

Sponsors & Cosponsors

Sponsor

  • Forrest Mandeville

    Republican • Senate

Cosponsors

There are no cosponsors for this bill.

Roll Call Votes

All Roll Calls

Yes: 320 • No: 72

Senate vote • 4/28/2025

Do Pass

Yes: 47 • No: 2

Senate vote • 4/25/2025

Do Pass

Yes: 44 • No: 4

Senate vote • 4/23/2025

Do Concur

Yes: 75 • No: 24

Senate vote • 4/22/2025

Do Concur

Yes: 76 • No: 24

Senate vote • 4/5/2025

Do Pass

Yes: 41 • No: 7

Senate vote • 4/4/2025

Do Pass

Yes: 37 • No: 11

Actions Timeline

  1. Chapter Number Assigned

    5/16/2025Senate

  2. Signed by Governor

    5/13/2025Senate

  3. Transmitted to Governor

    5/5/2025Senate

  4. Signed by Speaker

    5/5/2025House

  5. Signed by President

    5/2/2025Senate

  6. Returned from Enrolling

    4/29/2025Senate

  7. Sent to Enrolling

    4/29/2025Senate

  8. 3rd Reading Passed as Amended by House

    4/28/2025Senate

  9. 2nd Reading House Amendments Concurred

    4/25/2025Senate

  10. Returned to Senate with Amendments

    4/23/2025House

  11. 3rd Reading Concurred

    4/23/2025House

  12. 2nd Reading Concurred

    4/22/2025House

  13. Committee Report--Bill Concurred as Amended

    4/16/2025House

  14. Committee Executive Action--Bill Concurred as Amended

    4/15/2025House

  15. Hearing

    4/7/2025House

  16. First Reading

    4/7/2025House

  17. Referred to Committee

    4/7/2025House

  18. Transmitted to House

    4/5/2025Senate

  19. 3rd Reading Passed

    4/5/2025Senate

  20. 2nd Reading Passed

    4/4/2025Senate

  21. Committee Report--Bill Passed as Amended

    4/3/2025Senate

  22. Committee Executive Action--Bill Passed as Amended

    4/2/2025Senate

  23. Hearing

    3/27/2025Senate

  24. Referred to Committee

    3/20/2025Senate

  25. First Reading

    3/18/2025Senate

Bill Text

  • Enrolled

    4/29/2025

    PDF

  • As Amended (Version 3)

    4/16/2025

    PDF

  • As Amended (Version 2)

    4/3/2025

    PDF

  • Introduced

    3/18/2025

    PDF

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