Montana Building Codes, Permits and Contractor Rules
Here’s every rule from our 50-state guides for Montana on one page: the residential building code, frost depth, retaining wall permits, the 811 dig law, drainage law, contractor licensing, deposit limits, mechanics lien deadlines, workers’ comp, planting zones and frost dates. Each section links the official source and the full 50-state comparison.
Montana at a glance
- Building code: 2024 IRC (applies where locally enforced)
- Frost depth: Set locally; often 36-48 in.
- 811 notice: 2 business days (facility owners must locate within 2 business days of notice; notice covers work starting within 10 days)
- Contractors: State registration required
- Deposits: No statewide cap
- Liens: 90 days from final furnishing
- Workers’ comp: 1+ employees
- Drainage rule: Modified common enemy
- Planting zones: 3a to 6b
| Topic | Montana | Compare |
|---|---|---|
| Residential building code | 2024 IRC (applies where locally enforced) | All states |
| Frost line depth | Set locally; often 36-48 in. | All states |
| Retaining wall permit | Montana adopts the 2021 IRC (ARM 24.301.154) and lists no change to its permit exemptions. | All states |
| 811 notice before digging | 2 business days (facility owners must locate within 2 business days of notice; notice covers work starting within 10 days) | All states |
| Contractor license | State registration required | All states |
| Deposit limit | No statewide cap | All states |
| Right to cancel | 3 business days, sales made at home | All states |
| Lien filing deadline | 90 days from final furnishing | All states |
| Workers’ comp required | 1+ employees | All states |
| Drainage between neighbors | Modified common enemy | All states |
| Planting zones (2023 USDA) | 3a to 6b | All states |
| Frost dates (NOAA) | Last frost early May (Billings) to mid-Jun (Butte); first frost early Sep (Butte) to early Oct (Billings) | All states |
Montana residential building code
- Code
- 2024 International Residential Code with Montana amendments (ARM Title 24, Chapter 301)
- How it applies
- Statewide, applies only where locally enforced
- In effect since
- September 26, 2026
- Code agency
- Montana Department of Labor & Industry, Building Codes Program
- Who enforces it
- The state building code does not apply to residential buildings with fewer than five units (or to farm and ranch buildings) unless the city or county has adopted it by ordinance. Cities and counties with certified programs enforce it.
- Good to know
- Montana's code moved to the 2024 IRC on September 26, 2026, but the state code only covers houses where your city or county has adopted it. Outside those areas, houses aren't inspected for the building code.
Compare building codes in all 50 states
Frost line depth in Montana
- Who sets it
- Local building department
- Local examples
- City of Billings: 42 in.
City of Helena: 42 in. minimum to bottom of footing
City of Bozeman: 36 in. one-story; 48 in. two-story - Typical range
- 36-48 in.; 42 in. in Billings and Helena
- Good to know
- Bozeman sets footing depth by building height rather than a single frost line.
Frost line depth in every state
Retaining wall permits in Montana
- Permit exemption
- Montana adopts the 2021 IRC (ARM 24.301.154) and lists no change to its permit exemptions. Confirm the 4 ft rule with your local building department or the state Building Codes Program.
- Who decides
- Your city or county building department decides where one exists; otherwise ask the state Building Codes Program.
- Good to know
- If your area has no local building department, ask the state Building Codes Program before you build.
Retaining wall permit rules in every state
811 dig law in Montana
- One-call center
- Montana 811
- Notice before digging
- 2 business days (facility owners must locate within 2 business days of notice; notice covers work starting within 10 days)
- Ticket good for
- 30 days: request a new locate if excavation hasn't occurred within 30 days of marking; notice covers work finished within 30 days
- Hand-dig zone
- 18 in. of the outside lateral dimensions on both sides of the facility ('reasonably accurate' marking)
- Homeowners
- Partial: 'excavation' covers any tools, but excludes homeowner/occupant gardening in an established garden area unless 12 in. or deeper, and homeowner/occupant landscaping unless mechanized equipment is used or soil is disturbed 12 in. or deeper. Agricultural work excluded below 18 in. (24 in. in some cases). Other digging requires a call.
- The law
- Mont. Code Ann. § 69-4-501 et seq.
- Good to know
- The law sets 2 business days as the facility owners' marking deadline rather than an explicit lead time for the excavator. Request a new locate if you haven't dug within 30 days of marking.
Drainage law and stormwater permits in Montana
- Rule
- Modified common enemy
- The rule
- Common enemy limited by reasonable care: a landowner need not accept upstream surface water and may divert it, but must use reasonable care, without malice or negligence, to avoid damaging adjoining property.
- Leading case
- Winkowitsch v. Glacier Electric Cooperative, Inc.. 2023 MT 228 (Nov. 28, 2023); citing Covey v. Brishka, 2019 MT 164, 396 Mont. 362, 445 P.3d 785 and O'Hare v. Johnson, 116 Mont. 410, 153 P.2d 888 (1944)
- What it means for your yard
- You can protect your land from runoff, but when you regrade or redirect water you must use reasonable care not to damage your neighbor's property; careless or unreasonable diversion can make you liable.
- Construction stormwater permit
- Montana Department of Environmental Quality (DEQ), Water Protection Bureau (MPDES): 1 acre or more of total land disturbance (or smaller if part of a larger common plan that will disturb 1 acre or more): MTR100000, effective Jan. 1, 2023 to Dec. 31, 2027
- State rules below 1 acre
- No statewide rule below the 1-acre permit found; check your county and town.
- Local rules
- Montana cities and counties may have their own grading and stormwater ordinances.
- Good to know
- Montana lets landowners fend off surface water, but you must use reasonable care not to damage a neighbor's property. State construction stormwater permits start at 1 acre.
Contractor licensing in Montana
- Statewide rule
- Registration
- Agency
- Montana Department of Labor & Industry – Construction Contractor Registration
- Who needs it
- All construction contractors with employees must register with the Department of Labor & Industry.
- When it applies
- Construction contractors with employees (no dollar threshold stated)
- Check a contractor
- Official lookup
- Good to know
- Registration is a business and workers' comp registration and does not test a contractor's skill; contractors without employees don't have to register. You can also call the Department of Labor & Industry at (406) 444-7734.
Contractor license requirements in every state
Contractor deposits and your right to cancel in Montana
- Deposit limit
- No statewide cap.
- Right to cancel
- Personal solicitation sales over $25 (cash or credit): may cancel until midnight of the third business day after signing (Mont. Code Ann. §§ 30-14-502, 30-14-504). Excluded: sales where the buyer started the contact, or already knew the seller and what was being sold before the pitch.
- The law
- Mont. Code Ann. §§ 30-14-501 to 30-14-508 (Personal Solicitation Sales)
- Good to know
- Montana's 3-day cancel right doesn't apply if you called the contractor first, so read the contract before you sign.
Contractor deposit limits in every state
Mechanics lien deadlines in Montana
- Lien deadline (prime)
- File the lien with the county clerk and recorder within 90 days after final furnishing of services or materials, or within 90 days after the owner files a notice of completion, and certify service of a copy on the owner of record (MCA 71-3-535).
- Lien deadline (sub/supplier)
- Same as prime; an unexpired notice of right to claim a lien must be on file when the lien is filed (MCA 71-3-531(6)).
- Preliminary notice (sub/supplier)
- Required on residential work of fewer than 5 units (commercial and 5+ family dwellings are exempt; so are laborers): notice of right to claim a lien to the contracting owner by certified mail or acknowledged personal delivery within 20 days after first furnishing, and file a copy with the county clerk and recorder within 5 business days. Late notice covers only work in the 20 days before it and after. The 45-day lender-funded extension does not apply to owner-occupied residences (MCA 71-3-531).
- Notice of intent
- Not required.
- Enforce within
- Action within 2 years after the lien is filed (MCA 71-3-562).
- Homeowner rules
- The filed notice of right to claim a lien lapses after 1 year unless continued, and a lien can't be claimed without one on file (MCA 71-3-531(6)).
- The law
- MCA Title 71, Ch. 3, Part 5 (Construction Liens), § 71-3-521 et seq.
- Good to know
- Montana subcontractors and suppliers on homes must mail the owner a notice of right to claim a lien within 20 days of starting and file a copy with the county, or lose lien rights for earlier work.
Mechanics lien deadlines in every state
Workers' comp requirements in Montana
- Who must carry it
- The Act covers employers broadly, with listed exemptions such as household/domestic and casual employment (MCA 39-71-401). No minimum headcount. In construction, a person working at locations other than their own business location must carry coverage unless they hold an Independent Contractor Exemption Certificate (ICEC) (MCA 39-71-401(3), 39-71-417).
- Owners and officers
- Exempt unless coverage is elected: sole proprietors, working partners and LLP members, and working members of member-managed LLCs; corporate officers and LLC managers owning 10% or more (alone or with listed relatives), and listed relatives of 10% owners (MCA 39-71-401(2)(d), (2)(r)). Independent contractors need an ICEC ($125, no test) or must elect coverage (MCA 39-71-417; Montana DLI).
- Subcontractors
- A business that hires an independent contractor who has not secured coverage is liable for benefits to the contractor's employees; if the hired worker is not truly independent and the work is part of the hirer's trade or business, the hirer is liable for all benefits (MCA 39-71-405(1)-(2)).
- Homeowners
- Household or domestic employment and casual employment are exempt (MCA 39-71-401(2)(a)-(b)); if contracted work is casual employment for the hirer, the contractor becomes the employer (MCA 39-71-405(3)).
- Penalties
- Uninsured employers can be assessed a penalty of double the premium they would have paid (minimum $200) and are liable for 100% of an injured worker's medical and wage-loss benefits, which the Uninsured Employers' Fund collects from them; the worker may also sue (Montana DLI UEF page; MCA 39-71-502 et seq.). Independent contractors can be fined up to $5,000 per violation for working without an ICEC or coverage, or for misrepresenting independent-contractor status (Montana DLI ICEC page).
- The law
- MCA Title 39, Ch. 71; §§ 39-71-401, 39-71-405, 39-71-417
- State agency
- Montana Department of Labor and Industry, Employment Relations Division
- Good to know
- Montana has no minimum employee count. In construction, anyone working without coverage needs an Independent Contractor Exemption Certificate, and a hiring contractor is liable for an uninsured sub's employees.
Workers' comp requirements in every state
Planting zones in Montana
- 2023 USDA zones
- 3a to 6b
- Coldest-night range
- −40°F to 0°F
- Warmest area
- Northwestern Montana valleys
- Example cities
- Billings: 5a, Missoula: 5b, Great Falls: 4b, Kalispell: 5b
- Good to know
- The northern plains along the Hi-Line have some of Montana's coldest winters, while the valleys of northwestern Montana are the mildest.
Frost dates in Montana
| Station | Last spring frost | First fall frost | Frost-free days |
|---|---|---|---|
| Billings South-central Montana | May 4 | October 7 | 156 |
| Missoula Western Montana valleys | May 16 | September 26 | 130 |
| Great Falls North-central plains | May 19 | September 24 | 126 |
| Butte Southwest mountains | June 13 | September 5 | 83 |
- Typical range
- Last frost early May (Billings) to mid-Jun (Butte); first frost early Sep (Butte) to early Oct (Billings)
- Good to know
- These are typical (50%) dates from NOAA's 1991–2020 climate normals, so about half of years still bring a 32°F night after the listed spring date. In Montana, the last spring frost at the stations listed ranges from early May around Billings to mid-June around Butte.
- Local frost or planting guide
- Montana State University Extension
Frequently Asked Questions
What building code does Montana use?
2024 International Residential Code with Montana amendments (ARM Title 24, Chapter 301). It applies as follows: statewide, applies only where locally enforced. Your local building department can confirm the edition and amendments for your address.
How deep is the frost line in Montana?
Frost depth is set by local building departments. Typical local values: 36-48 in.; 42 in. in Billings and Helena. Footings for houses, additions and attached decks go below it.
How much can a contractor ask for up front in Montana?
No statewide cap. Cancel rights: Personal solicitation sales over $25 (cash or credit): may cancel until midnight of the third business day after signing (Mont. Code Ann. §§ 30-14-502, 30-14-504). Excluded: sales where the buyer started the contact, or already knew the seller and what was being sold before the pitch.
How long does a contractor have to file a mechanics lien in Montana?
File the lien with the county clerk and recorder within 90 days after final furnishing of services or materials, or within 90 days after the owner files a notice of completion, and certify service of a copy on the owner of record (MCA 71-3-535). Subcontractors and suppliers may have different notice rules; see the section above.
What planting zone is Montana?
On the 2023 USDA map, Montana runs from zone 3a to 6b. Examples: Billings 5a, Missoula 5b, Great Falls 4b. Enter your ZIP on the USDA map for your exact zone.
Do contractors need workers' comp in Montana?
The Act covers employers broadly, with listed exemptions such as household/domestic and casual employment (MCA 39-71-401). No minimum headcount. In construction, a person working at locations other than their own business location must carry coverage unless they hold an Independent Contractor Exemption Certificate (ICEC) (MCA 39-71-401(3), 39-71-417). Owner exemptions and subcontractor rules are in the workers’ comp section above.
When is the last frost in Montana?
At the NOAA stations we list: Last frost early May (Billings) to mid-Jun (Butte); first frost early Sep (Butte) to early Oct (Billings). These are typical (50%) dates from the 1991–2020 climate normals, so about half of years still bring a 32°F night after the spring date.
This page is general information, not legal or tax advice. Rules change; the agencies and statutes linked above have the final word.
Montana in each 50-state guide: Frost line depth · 811 dig laws · Retaining wall permits · Contractor licensing · Contractor deposit limits · Building codes · Planting zones · Mechanics lien deadlines · Workers' comp · Frost dates · Drainage laws · Noxious weed laws · Rainfall and snowfall · Landscaper pay · Pesticide applicator licensing · Landscaping sales tax · All state guides
Last checked October 31 and November 1, 2026 against official state and local sources for this state. Rules change; your state agency or local building department has the final word. Spot something out of date? Email info@muthlerlandscaping.com and we’ll fix it.
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Cite as: Muthler Landscaping & Construction, “Montana Building Codes, Permits and Contractor Rules,” https://muthlerlandscaping.com/state-guides/montana/ (last checked November 9, 2026).
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