State Guide · Verified 2026
Deck Construction Permits in Montana
There is no single statewide building code, so the rule is set by your local jurisdiction; most still require a permit for any deck attached to the house or more than 30 inches above grade.
The Building Code in Montana
Montana statewide code (2021 I-Codes), Building Codes Program, with a residential permit exemption that doesn't clearly extend to decks
The Montana Building Codes Program, within the Dept. of Labor and Industry, adopts a uniform statewide code based on the 2021 International Codes and enforces it directly in any city, county, or town that has not established its own certified local program. Montana state law separately exempts residential buildings under five dwelling units, along with private garages and storage buildings, from the state building permit requirement. Unlike sheds, which clearly fall under this garage-and-storage exemption, decks are generally treated as part of the primary residential structure's permit process, and cities with their own certified programs, including Billings, Missoula, Bozeman, and Helena, require local permits for deck construction over 30 inches above grade. Montana has no single statewide ground snow load value; it must be determined from local Authority Having Jurisdiction data, a structural engineer, or the "Snow Loads for Structural Design in Montana" publication.
Quick Facts
Who Sets the Rules
A state exemption that treats decks differently than sheds
Montana's state law exempts private garages and storage buildings from state building permits, but decks are generally handled as part of the primary residential permit process rather than under that specific accessory-structure exemption, meaning most major cities still require a deck permit despite the state's hands-off approach to garages.
Major cities fill the gap with their own local programs
Billings, Missoula, Bozeman, and Helena all run certified building code programs and require local permits for decks over the standard 30-inch height threshold, closing the practical gap the state exemption leaves open for other structure types.
No single statewide number for one of the most important design factors
Unlike most states, Montana has no single statewide ground snow load value at all. Design values must be pulled from local Authority Having Jurisdiction data, a structural engineer, or a dedicated state publication, "Snow Loads for Structural Design in Montana," a genuinely decentralized approach to a critical structural figure.
A real, lasting consumer disclosure requirement
Montana requires a permanent Energy Code Compliance Label affixed directly to the home's electrical breaker box, certifying the house meets minimum insulation, window, and heating system efficiency standards, ensuring that information isn't lost when the home changes owners.
Wildfire exposure adds real requirements in some areas
Properties in Wildland-Urban Interface zones may face requirements for fire-resistant materials, ember-resistant vents, and defensible space, requirements that can directly affect deck material choices and clearance from structures.
What people get wrong
The most common mistake is assuming Montana's state-level exemption for garages and storage buildings also covers decks. In practice, the major cities where most Montanans live treat deck construction as needing its own local permit, regardless of that state exemption.
Counties With Their Own Rules
These Montana counties have verified, county-specific deck construction rules that differ from the state baseline:
Check Your County
Select your county for the local rule, fees, and your building department's contact details:
Building It Yourself? Here's What You'll Need
Popular tools and materials homeowners use for a deck construction project:
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Official Sources
Rules change and cities within a county may differ. This guide is general information, not legal advice — always confirm with your local building department. Reviewed by the StateDataIndex Editorial Team · Updated September 2026.