Billings Basement Bedroom Rules: What the City's Egress Page Actually Requires

September 4, 2026

Search “egress windows Billings” and the top result is a page on the City of Billings website titled “What are the requirements for egress windows?” It is short. It says the minimum opening area under IRC Section 310 is 5.7 square feet, the minimum opening height is 24 inches, the minimum opening width is 20 inches, and the bottom sill can be no more than 44 inches from the floor, and it invites you to call the Building Division with questions. Those four numbers are correct and they are the ones that matter most. They are also about a third of what an inspector actually checks.

This post fills in the rest: where those numbers come from, what the code says about wells, ladders, and covers that the city page leaves out, how the Billings permit actually works, and what changes the moment your address is outside city limits.

Where the numbers come from

Montana adopts the International Residential Code statewide through Administrative Rules of Montana 24.301.154. The current edition is the 2021 IRC, effective June 11, 2022. The City of Billings adopted the same 2021 IRC, along with the 2021 IBC and the 2020 National Electrical Code, effective September 1, 2022, and its Building Division FAQ lists those editions.

Montana amends the IRC in a handful of places: stair risers up to 8 1/4 inches, treads down to 9 inches, guards at 30 inches, footing exceptions, residential fire sprinklers deleted. None of the amendments touch Section R310. So the emergency escape and rescue opening rules in Billings are the national 2021 IRC rules, unmodified.

The full R310 checklist

Section R310 requires an emergency escape and rescue opening in every sleeping room and in basements with habitable space. One per bedroom, not one per basement. The opening has to open directly to the outside or to a well, and it has to work from inside without keys, tools, or special knowledge. Then the numbers:

Items 1 through 4 are on the city page. Items 5 through 8 are what the city inspector also measures, and what the window well installation and covers and drainage pages are about.

Two mistakes the numbers invite

“Net clear” is the hole, not the window. Measure the opening with the sash fully open. A slider only opens half its width, so a 4-foot-wide slider gives you 2 feet of clear width. To clear 5.7 square feet with a slider you need a large unit, roughly 4 feet by 4 feet or more. An in-swing casement swings the whole sash clear and hits the number in a much smaller opening. Windows with an “egress” sticker at the store only comply in specific sizes and styles; the sticker is marketing until you do the math for your hole.

The minimums do not stack. A 24-inch by 20-inch opening is 3.3 square feet. It meets both dimension minimums and fails the area minimum by nearly half. One dimension has to be generous.

What the Billings permit actually looks like

Cutting a foundation opening inside city limits is a building permit. Here is the process as the Building Division runs it:

• Online only. The city requires online submission for all permits through its CityView portal. No counter drop-off.
• Plans. Residential remodels need two sets of building plans. For an egress cut that means a simple drawing showing the opening location, size, lintel, and well.
• Review time. The city quotes four to seven business days for the initial review of a complete residential application, once any special issues like variances are addressed.
• Fees. Based on valuation; for remodels, the contract price or the estimated value of labor and materials. Figure $150 to $600 with locates and handling, itemized on our quotes.
• Inspection. A final inspection once the window, well, and drainage are done. Pass it, and the room is a conforming bedroom.

We handle all of that as part of every egress window installation inside the city. What we will not do is guarantee the outcome; the permit and inspection belong to the city.

Outside city limits, the rules change completely

This is the part almost nobody in Billings knows until they buy a house in Lockwood. The city’s own FAQ, “What if I am not in the Billings jurisdiction?”, says the State of Montana governs the area outside city limits and points to the state Building Codes Program. The state program issues permits for commercial buildings and exempts residential buildings with fewer than five dwelling units. Yellowstone County has no building program and issues no building permits or certificates of occupancy outside Billings.

Put those together and an egress cut on a house in Lockwood, Shepherd, or Huntley has no building permit, no plan review, and no inspection. State permits still cover the electrical, plumbing, and mechanical work in the basement finish. Laurel is the exception: it is a certified jurisdiction with its own city building department, and Laurel homes get a Laurel permit and inspection. Columbus, in Stillwater County, has no local program either.

Does the code still apply out there? The IRC is Montana’s residential code statewide; what is missing is enforcement. Practically, the people who will measure your opening are the home inspector working for your buyer and the appraiser deciding whether the room counts. Both use the R310 numbers. That is why we build to R310 in Lockwood exactly as we do on Grand Avenue, and it is why “no inspection out here” is never a reason to accept a smaller lintel. Our Lockwood, Shepherd, and Huntley pages go into the local details.

Radon, briefly, because everyone asks

Montana is heavily radon country: the EPA map puts 49 of the state’s 56 counties in Zone 1, the highest-potential zone. Yellowstone County is one of the seven mapped Zone 2, moderate potential, while Stillwater County to the west is Zone 1. Radon has nothing to do with egress code. It has a lot to do with why Billings basements get finished and lived in, and every finished sleeping room needs an R310 opening. EPA’s advice is to test every home regardless of zone. If you are finishing a basement bedroom, test first, plan mitigation if needed, and cut the egress opening in the same season so the foundation is disturbed once.

The order of operations for a Billings basement bedroom

1. Test for radon. Decide on mitigation.
2. Measure the existing opening against the checklist above. Most Billings basement windows fail all four city numbers.
3. Get the egress quote and, inside the city, submit the permit through CityView. Four to seven business days.
4. Cut, set, drain, and backfill: one to two days on site. The egress cut is the first trade on a finish, before framing.
5. Frame, wire (state electrical permit), insulate, drywall, finish.
6. Final inspection. The bedroom counts.

Dig season is roughly March through November; Billings designs to a 36-inch frost depth, and the ground does not always cooperate in January. If the goal is a legal bedroom by summer, get measured in fall. Already finished and worried the room does not comply? Start at code compliance upgrades. Prices for all of it are on the pricing page: full installs run $3,500 to $6,500, and the free on-site measure turns that into one flat number.