What Can You Build Without a Permit in Montana? (2026)
The 30-second answer for Montana
In Montana, the projects you can usually build without a building permit are a small detached shed, a short freestanding deck, a fence under the height cap, a low retaining wall, and cosmetic interior work. The exact limits Montana enforces are in the table below — and your city can be stricter than the state. The catch every homeowner needs to hear: even when no permit is required, the building code, zoning setbacks, and any HOA rules still apply. Permit-exempt means the paperwork is waived, not the rules.
How Montana sets the rules
Montana adopts the 2021 IRC and 2021 IBC (effective June 11, 2022) through the Dept. of Labor & Industry Building Codes Bureau under ARM Title 24, Chapter 301. But per MCA 50-60-102 the state code does NOT apply to — and the state will NOT enforce it for — homes with fewer than five dwelling units, farm/ranch buildings, or owner-use private garages, unless a local government adopts enforcement by ordinance. As a result, residential building permits are only enforced inside certified city/county programs such as Billings and Missoula; many rural Montana areas require no residential building permit at all.
Permit-exempt limits in Montana
These are the thresholds we verified for Montana. Treat each one as the most you can usually do without pulling a permit — a stricter city amendment always wins.
| Project | Montana permit-exempt limit |
|---|---|
| Detached shed / accessory building | Follows the 2021 IRC baseline, adopted unchanged: a one-story detached accessory building (tool/storage shed, playhouse) of 200 sq ft or less needs no building permit. Billings confirms detached sheds not exceeding 200 square feet, and Missoula confirms 200 sq ft for residential (120 sq ft for commercial). The shed cannot be habitable, and zoning setbacks/height limits — and often a zoning permit — still apply. |
| Deck | Follows the 2021 IRC R105.2 baseline (adopted without amendment). A deck is permit-exempt only if ALL apply: 200 sq ft or less, not more than 30 inches above grade at any point, not attached to the dwelling, and not serving the required exit door. Missoula adds that it must also have no roof or arbor. Anything larger, higher, attached, or covered requires a permit in Billings and Missoula. |
| Fence | The state/IRC building-code threshold is a fence over 7 feet, but both cities require a separate zoning/planning fence permit well below that. Billings requires a Planning Department fence permit for fences roughly 3-6 feet (a building permit plus 105 mph wind-load engineering at 7 ft and taller); Missoula requires a fence permit regardless of height (building permit over 7 ft). Building-permit-exempt is not permit-free here. |
| Retaining wall | Follows the IRC baseline: no building permit for a retaining wall 4 feet or less measured from the bottom of the footing to the top of the wall, provided it supports no surcharge. Over 4 feet, or any height that supports a surcharge/slope, requires a permit. Billings additionally requires a Montana-licensed engineer wet-stamped design for walls 4 ft+ or any wall with a surcharge. |
| Patio (on grade) | On-grade concrete patios, sidewalks, and driveways that do not support a structure are generally permit-exempt — Billings lists sidewalks and driveways as exempt, and the IRC exempts slabs/walks not more than 30 inches above grade and not over a basement. Zoning impervious-surface/lot-coverage limits and setbacks can still apply. Verify locally — confirm with your local building department. |
Baseline: 2021 International Residential Code, Section R105.2. See the national project-by-project guide for how each threshold works.
Can you do the work yourself in Montana?
Yes. A homeowner may pull the permit and do the work on their own residence in certified jurisdictions like Billings and Missoula. Montana exempts an owner working on their own property from construction-contractor registration (MCA 37-45-104, formerly 39-9-211); however, that exemption is lost if you build with intent to promptly sell unless you've occupied the home as your primary residence for at least 12 months. Some jurisdictions require an owner-builder affidavit — confirm locally.
What's different about Montana
Much of rural Montana has no residential building permit
Under MCA 50-60-102 the state building code does not apply to — and the state cannot enforce it for — homes under five units, farm/ranch buildings, or owner-use garages unless the local city or county has adopted an enforcement program. Many unincorporated/rural areas therefore issue no residential building permit; the code protections still exist on paper but nobody inspects.
Fences: building-permit-exempt does not mean permit-free
The 7-ft IRC building-permit threshold is only half the story. Billings requires a Planning Department fence permit at roughly 3-6 feet, and Missoula requires a fence permit for a fence of any height. Homeowners assuming a short fence needs nothing routinely get caught by the separate zoning permit.
Farm/ranch buildings and owner-use garages are statewide-exempt
MCA 50-60-102 places farm and ranch buildings of any size, and private garages or storage structures of any size used only by the owner, outside the state building code entirely — unless the local legislative body opts them in. This is broader than the IRC's 200 sq ft accessory exemption.
"Permit-exempt" does not mean rule-free
I spent 25 years as a firefighter before I built PermitDeck, so let me be blunt about the part that gets people hurt. "No permit" never means "no rules." When a project is exempt in Montana, three things are still true — and now you are the one responsible for them, because no inspector is coming to check:
- Building code still applies. An exempt deck in Montana still has to meet the structural rules of IRC R507 — real footings, a proper ledger, and guards. A shed still has to carry your local snow and wind load. The code does not care whether a permit was pulled.
- Zoning and setbacks still apply. Exempt does not mean you can put it anywhere. Setbacks from property lines, easements, lot-coverage caps, and corner-lot sight lines all still bind you — and a neighbor complaint can force you to move it.
- HOA rules are separate. Your HOA architectural review is a private contract, not a government permit. You can be fully permit-exempt with your city and still be forced by your HOA to tear something out.
The big Montana cities
Permits are pulled locally, so your city's building department has the final word. Here are the two largest, with a link straight to their office.
Billings
Certified jurisdiction enforcing the 2021 IRC. Exempts detached sheds up to 200 sq ft; decks/roofing/parking lots generally need permits. Fences 3-6 ft need a Planning permit, 7 ft+ need a building permit with 105 mph wind-load engineering; retaining walls over 4 ft (or any wall with a surcharge) need a building permit and a Montana-licensed-engineer stamp.
Billings building departmentMissoula
Certified jurisdiction. No building permit for residential sheds under 200 sq ft (commercial under 120 sq ft). Freestanding decks are exempt only if 30 in or less above grade, under 200 sq ft, unattached, no roof/arbor, and not serving the egress door. All fences require a fence permit regardless of height (building permit over 7 ft).
Missoula building departmentTurns out you do need a permit? We'll match you with pros who pull it
If your project crosses one of these Montanathresholds, the cleanest path is to hire a licensed pro who pulls the permit in their own name and stands behind the inspection. Tell us the project once and we'll send it to up to three verified local pros. It's free, it's capped at three, and we never sell your information — the opposite of the lead-farm sites.
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What happens if you needed a permit and skipped it
Guessing wrong on the exemption is not a small risk. The common outcomes are a stop-work order, a fine (often double the normal permit fee), and being ordered to open finished work back up for inspection or tear it out. The expensive part usually lands later: unpermitted work routinely kills a home saleat the buyer's inspection, and an insurance claim can be denied if the damage traces back to unpermitted construction. Most jurisdictions do allow a retroactive (after-the-fact) permit — it costs more, but it clears the record.
Full detail: what happens if you build without a permit and how to get a building permit.
Montana permit-exemption FAQs
Do I need a building permit for a shed in Montana?
Not for a detached one-story shed of 200 square feet or less — that's exempt statewide under Montana's adopted 2021 IRC, and Billings and Missoula both confirm the 200 sq ft cutoff (Missoula caps commercial sheds at 120). The shed still can't be habitable, and zoning setbacks, height limits, and possibly a zoning permit apply. In many rural areas there is no building permit at all.
Does rural Montana actually require building permits for a house?
Often not. Under MCA 50-60-102 the state building code doesn't apply to — and the state won't enforce it for — homes under five units, farm/ranch buildings, or owner-use garages unless the local city or county has adopted enforcement. Many rural Montana areas therefore issue no residential building permit. Billings and Missoula, by contrast, are certified jurisdictions that do inspect and enforce.
Do I need a permit for a fence in Billings or Missoula?
Almost certainly a zoning permit, even below the 7-foot building-code threshold. Billings requires a Planning Department fence permit for fences roughly 3-6 feet (a building permit plus 105 mph wind-load engineering at 7 feet and taller). Missoula requires a fence permit regardless of height, with a building permit over 7 feet. Being building-permit-exempt does not make a fence permit-free in these cities.
Can I build a deck without a permit in Montana?
Only a small ground-level one. Montana's adopted 2021 IRC exempts a deck only if it is 200 square feet or less, no more than 30 inches above grade, freestanding (not attached to the house), and not serving the exit door; Missoula adds that it must have no roof or arbor. Anything larger, higher, attached, or covered needs a permit in Billings and Missoula.
Sources we verified against
- Montana DLI Building Codes Bureau — Current Codes (2021 IRC/IBC, eff. 6/11/2022)
- MCA 50-60-102 — Applicability (state code excludes <5-unit homes, farm/ranch, owner garages)
- City of Billings — What permits are required? (200 sq ft shed exemption)
- City of Billings — Fences & Retaining Walls
- City of Missoula — Building Permit FAQ (200 sq ft sheds; deck rules; all fences need a permit)
Every threshold on this page is anchored to Montana's building code or the sources listed above. Where a number varies by city and we could not verify it, we say "verify locally" rather than guess — a permit page you cannot trust is worse than no page at all.
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