A legal basement bedroom in Minnesota needs its own emergency escape opening with at least 5.7 sq ft of net clear opening (5.0 sq ft for a below-grade or grade-floor window), at least 20 in of clear width and 24 in of clear height, and a sill no more than 44 in above the finished floor. A below-grade window needs a well with at least 9 sq ft of area and 36 in of projection, plus a permanent ladder if the well is deeper than 44 in.
The room also needs at least 70 sq ft with no dimension under 7 ft, at least 6 ft 4 in of ceiling in an existing basement, permanent heat to 68°F, a smoke alarm inside and outside the room, and a CO alarm within 10 ft, all under a permit. A closet is not a code requirement.
On this page
- What makes a basement bedroom legal in Minnesota?
- How big does a basement egress window have to be?
- What are the window well requirements?
- What does cutting a new egress opening in a foundation involve?
- Which window type works best for basement egress: casement, slider or hopper?
- What else does a basement bedroom need besides a window?
- How does an egress bedroom fit the reference Twin Cities basement?
- Questions people ask
What makes a basement bedroom legal in Minnesota?
A basement room is a legal bedroom when it has its own emergency escape and rescue opening, enough floor area and ceiling height, permanent heat, and the right smoke and carbon monoxide alarms, all built under a permit and passed by your city's inspector. The window is the part that costs real money and changes the outside of the house, so it is where I start.
Minnesota builds to the Minnesota Residential Code, which is the 2018 International Residential Code adopted with state amendments in Minnesota Rules chapter 1309. The escape-opening rule is Section R310, and Minnesota amends it in part 1309.0310. Two of those amendments matter most in a basement finish:
- Every basement sleeping room needs its own opening. Where a basement has sleeping rooms, each one gets an escape opening; the adjoining areas of the basement do not need separate ones.
- New bedrooms in an existing basement must comply. Plain alterations or repairs to an existing basement do not trigger an escape opening, but a new sleeping room created in an existing basement does (R310.6 and R310.6.1, as amended).
There is a sprinkler exception: a basement or basement bedroom in a house protected by an automatic sprinkler system (IRC P2904 or NFPA 13D) is exempt, but only if the whole basement, its egress path to the exit level and the open areas on that level are sprinklered. Retrofitting that into a finished house is rarely the cheaper path, so in practice every basement bedroom I lay out gets a window.
A room labeled "office" or "den" with a closet and no egress window is a common shortcut. If anyone will sleep there, design it as a bedroom. The escape opening is a life-safety rule, not a resale label.
How big does a basement egress window have to be?
The size rule is about the net clear opening: the hole a person can actually climb through with the window fully open, not the frame size on the order sheet. Here are the R310 numbers as Saint Paul's code handout lays them out for the 2020 Minnesota Residential Code:
| Requirement | Minimum or maximum | What it means in practice |
|---|---|---|
| Net clear opening area | 5.7 sq ft (821 sq in) | Measured with the operable part fully open |
| Grade-floor or below-grade opening | 5.0 sq ft | Applies to most basement windows; Savage and Prior Lake describe this as a sill within 44 in of grade |
| Net clear height | 24 in minimum | Clear height of the opening, not the sash |
| Net clear width | 20 in minimum | Clear width of the opening, not the frame |
| Sill height | 44 in maximum above the finished floor | Measured to the bottom of the clear opening |
| Operation | From inside, without keys, tools or special knowledge | Window opening control devices must meet ASTM F2090 |
Note the trap in those numbers: 24 in by 20 in is only 480 sq in, which is about 3.3 sq ft. Hitting the minimum height and width does not get you to the minimum area. You need both dimensions and the area. A clear opening of 24 in wide by 30 in high is 720 sq in, which is exactly 5.0 sq ft, so I treat that as the floor, and I design bigger.
The 5.0 sq ft figure is part of the base IRC text for grade-floor and below-grade openings, not a Minnesota-only rule, and the state amendments in 1309.0310 do not change the 5.7 / 5.0 / 24 / 20 / 44 numbers. Minnesota's amendment adds a stricter set for rooms used for licensed foster care or day care: at least 20 in wide, 20 in high, 648 sq in (4.5 sq ft) clear and a sill no higher than 48 in, applied together with the general rule, whichever is more restrictive. If you run or plan a licensed home day care in the basement, tell your designer up front.
The sill height is measured from the finished floor
The 44 in maximum is from the finished floor, so the floor build-up counts. If you add a subfloor panel and plank flooring, the sill gets closer to the floor, which helps. If the opening is cut too high and you try to fix it with a built-in step or a bench under the window, check with your city before you build; the handouts I used measure to the floor, and inspectors do not all accept a step as the floor.
Replacement windows have their own rule
Replacing an existing egress window is different from creating a bedroom. R310.2.5 lets a replacement window skip the area and sill-height rules if it is the manufacturer's largest standard size that fits the existing frame or rough opening, matches the existing operating style or gives equal or greater opening area, and is not part of a change of occupancy. That exemption does not help when you turn an unfinished basement into a bedroom; a new sleeping room in an existing basement has to meet R310.1.
What are the window well requirements?
Most basement egress windows sit below grade, so they need a window well. The well is part of the escape path, and the code sizes it for a person climbing out, not for light.
| Well rule (R310.2.3) | Requirement | Design note |
|---|---|---|
| Horizontal area | 9 sq ft minimum | Measured inside the well |
| Projection and width | 36 in minimum each way | Projection is out from the foundation; width is along the wall |
| Window must open fully | Within the well | A casement sash swinging into the well must still leave 9 sq ft clear when open (Saint Paul diagram) |
| Ladder or steps | Required when the well is deeper than 44 in | May encroach up to 6 in into the required well dimensions |
| Ladder rungs | 12 in minimum inside width, 3 in minimum projection from the wall, 18 in maximum on center | Permanently affixed, usable with the window fully open, for the full height of the well |
| Drainage (R310.2.3.2) | Connected to the foundation drain system or an approved alternative | Not required on well-drained Group I soils |
A 36 in by 36 in well is exactly 9 sq ft, so a square well at the minimum works on paper. The catch is the ladder: it may only eat 6 in of the required dimensions, and a casement sash swinging into a tight well can eat the rest. On deep wells I specify a well with projection to spare.
The ladder trigger is the vertical depth of the well, not the sill height inside. A well that is 44 in deep or less needs no ladder; one inch deeper and it needs one. Many manufactured wells have steps molded into the wall. Basement Systems, for one, describes built-in steps on its egress well. Make sure the steps still meet the rung width, projection and spacing rules.
Two site rules come from zoning and from what's above the window. Prior Lake requires a basement egress window to sit at least 5 ft from the property line and keeps it out of drainage and utility easements. An opening under a deck or porch must open fully and leave a path at least 36 in high to a yard or court. Saint Paul's diagram also recommends a 36 in guardrail when a well sits next to a property line or sidewalk. For snow, ice, covers and drainage, see my companion post on egress window wells in a Minnesota winter.
What does cutting a new egress opening in a foundation involve?
The 1985 to 2015 basements I design around typically came with small windows set high in the wall. They are fine for light and useless for escape, so a bedroom almost always means cutting a new, larger opening or enlarging an existing one. That is structural work on the foundation, and the city reviews it as structural work.
What the permit drawings have to show
Prior Lake's egress handout is a good checklist of what a city wants before it issues the permit:
- A certificate of survey or scaled site plan showing property lines, existing buildings and the proposed well.
- Building plans with all structural members sized to support the loads.
- Scaled dimensions of the window and well.
- A full elevation of the altered wall, including the floor level and the stories above.
- A section showing the header size, sill height above the floor and well depth.
- The type and size of all materials.
Prior Lake then inspects the framing before interior and exterior coverings go on and the well is finished, and does a final once the window is fully framed and the work is done. Other cities run it differently, so check with yours; I cover the full permit sequence in my guide to basement permits in Minnesota.
Poured versus block walls
The question every drawing answers is how the load above the new opening gets carried around it. On a poured wall, the opening is saw-cut; Basement Systems describes cutting the opening with a masonry saw and then sealing and fastening the well's flanges to the outside of the foundation. On a block wall, the cut runs through hollow units, so the drawing has to show how the edges are closed and what spans the opening. In both cases the header or lintel is something your city's plan reviewer signs off on, not something to improvise on site. If your reviewer asks for an engineer's detail, it is time well spent.
Digging, utilities and water
The well hole is excavation next to the house, so the utility locate comes first. Prior Lake's handout tells you to call Gopher State One Call before digging and gives both 48 hours and two days' notice through 811. Confirm the current timing before anyone digs. The new opening is also a new joint in your foundation's water defense. The window needs to be sealed into the opening, the well sealed to the wall, and the well floor drained so water never stands against the glass. Basement Systems notes that water pooling in a well can leak around the window opening. In a house with an interior drain tile and sump, the well's drain is part of that system; see my sump pump guide and basement moisture guide.
Which window type works best for basement egress: casement, slider or hopper?
The operating style decides how much of the frame turns into clear opening. That is why window type is the most important line in an egress spec.
| Window type | How it opens | Egress fit | Where I use it |
|---|---|---|---|
| Casement | Side-hinged sash swings fully out | Best. Nearly the whole frame becomes clear opening, so the smallest frame passes | My default for basement bedrooms. Plan the well so the open sash still leaves 9 sq ft clear |
| Horizontal slider | One sash slides over the other | Works, but only the moving half is clear opening, so the frame has to be roughly twice as wide | Shallow, wide openings, or when a sash swinging into the well is a problem |
| Single- or double-hung | Sash slides vertically | Same half-opening problem, turned vertical; usually too tall for a basement wall | Rarely in basements |
| Hopper or awning | Sash tilts on a hinge at the bottom or top | Poor. The tilted sash sits in the escape path | Light and ventilation windows in other rooms, not the bedroom's escape opening |
Here is the arithmetic that sells me on casements. A casement with a clear opening of 24 in wide by 36 in high gives 864 sq in, or 6.0 sq ft. That clears both the 5.0 and 5.7 sq ft thresholds in a compact frame. To get the same 5.0 sq ft from a slider at a 24 in clear height, the moving sash alone needs a 30 in clear width, so the whole unit is about twice that wide. In a basement where the wall above the window is full of ducts and the space beside it holds a closet, the narrower casement is easier to place.
Whatever type you choose, ask the window supplier for the net clear opening dimensions, not the rough opening. Manufacturers publish both, and only the clear opening counts. Prior Lake also lists a minimum U-factor of 0.32 for these windows, which is an energy-code number. Check with your city.
What else does a basement bedroom need besides a window?
| Requirement | Rule | Source |
|---|---|---|
| Floor area | 70 sq ft minimum, and no horizontal dimension under 7 ft | IRC R304.1 and R304.2 (Saint Paul basement finish handout) |
| Ceiling height | 7 ft for habitable space; 6 ft 4 in in an existing basement, including beams, girders, ducts and other obstructions | MN R305.1 and R305.2.1 (Minnesota Rules ch. 1309) |
| Heat | A permanent heat source able to keep the room at 68°F | R303.10 (Saint Paul basement finish handout) |
| Smoke alarms | In each bedroom and outside each bedroom in the immediate vicinity, and on every level | R314.3 (Saint Paul, Savage, Prior Lake handouts) |
| Carbon monoxide alarms | Outside and not more than 10 ft from each bedroom | MN R315.3 (Minnesota Rules ch. 1309) |
| Fuel-burning appliances | Not located in, or taking combustion air from, a bedroom unless specific conditions are met, such as direct-vent units | 2020 MN Fuel Gas Code 303.1 (Saint Paul handout) |
Smoke alarm upgrades reach beyond the basement
Finishing a basement bedroom usually triggers alarm work upstairs too. Savage's handout says smoke alarms are required throughout the house when you remodel or finish a basement. New alarms in the remodeled areas must be hardwired and interconnected with battery backup, while alarms in existing areas may be battery powered. Minnesota's amendments to R314 and R315 carry the same idea: interconnection in existing areas is not required, and alarms installed there may run on batteries. Chanhassen requires smoke alarms on all levels and in every sleeping room, existing areas included.
Is a closet required for a bedroom?
Not by the building code. None of the Minnesota Residential Code sections or Twin Cities handouts I checked list a closet as a sleeping-room requirement; they list the escape opening, area, ceiling height, heat and alarms. Whether a room without a closet gets marketed or appraised as a bedroom is a real-estate question, not a code question. Ask your agent. I almost always design one in anyway, because a basement bedroom without storage gets used as storage.
Ceiling height around the duct trunk
The 6 ft 4 in rule for existing basements is measured to the bottom of the beam or duct, not the joists. In a reference basement with roughly 8 ft to the joists, the main trunk and the beam are what decide where the bedroom goes. I keep the bedroom out from under the trunk where I can, and use the soffit for the hallway. My layout and zoning guide works through that.
How does an egress bedroom fit the reference Twin Cities basement?
Take my reference house: a suburban two-story in Lakeville or Shakopee, built around 2000, with a poured foundation, about 8 ft to the joists, a main duct trunk and a steel beam running the length of the house, the sump in one corner and the furnace and water heater in another, and around 1,000 sq ft to finish. Here is how I place the bedroom.
- Pick the wall from the outside first. The well needs a 36 in projection, a 5 ft property-line setback in Prior Lake and room to dig. That usually rules out the side yard on a tight suburban lot, and it rules out walls under a deck unless there is a 36 in high path out. The back wall away from the deck is the usual winner.
- Keep it off the mechanical corner. The bedroom cannot borrow combustion air from the furnace room, and you want the mechanical room door in a hallway, not in the bedroom. I put the bedroom on the opposite end from the furnace and water heater.
- Check the well depth against 44 in. If grade sits about 72 in above the basement floor and the sill sits at 40 in, the well floor ends up a little below the sill, a bit over 32 in below grade before gravel. That is under the ladder threshold. Drop the sill or raise the grade and you are over 44 in and need steps. I measure this on site before choosing a well.
- Use a casement. A casement with a 24 in by 36 in clear opening (6.0 sq ft) meets the rule with a compact frame and leaves the wall beside it free for a closet.
- Size the room to the code minimums with room to live. 70 sq ft and 7 ft is the floor; a basement bedroom that people actually want to sleep in is closer to 11 by 12, with a closet on the interior wall.
- Plan heat and alarms with the bedroom. A supply run off the trunk and a return so the room holds 68°F, a hardwired interconnected smoke alarm in the room and one outside it, and a CO alarm within 10 ft of the door.
The egress window is the single most expensive line in a bedroom finish, and it changes the outside of the house. That is why I lock it in before anything else in the plan. For overall budgets, see what a basement costs in the Twin Cities and the three budget tiers.
Check with your city: egress handouts, setback rules, whether a well needs a guardrail, and inspection sequences vary between Lakeville, Prior Lake, Savage, Chanhassen, Saint Paul and every other Twin Cities city. The R310 numbers are statewide; the paperwork is local.
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Design my basement with EmmaQuestions people ask
What size egress window do I need for a basement bedroom in Minnesota?
The net clear opening must be at least 5.7 sq ft, or 5.0 sq ft for a grade-floor or below-grade opening, with at least 24 in of clear height and 20 in of clear width. The sill can be no higher than 44 in above the finished floor. Those are clear-opening dimensions with the window fully open, not frame sizes.
Does every basement bedroom need its own egress window?
Yes. Minnesota's amendment to R310.1 requires an emergency escape and rescue opening in each basement sleeping room. The adjoining basement areas do not need their own. The exception is a house where the whole basement and its egress path are protected by an automatic sprinkler system.
When does a window well need a ladder?
When the well is deeper than 44 in. The ladder or steps must be permanently attached, at least 12 in wide inside, project at least 3 in from the wall and have rungs no more than 18 in apart for the full depth of the well. They may encroach up to 6 in into the required 9 sq ft, 36 in well.
How big does an egress window well have to be?
At least 9 sq ft of horizontal area, with at least 36 in of projection and 36 in of width, and the window must be able to open fully inside it. If a casement sash swings into the well, the well still needs 9 sq ft clear with the sash open.
Do I need a permit to cut an egress window in my basement?
Yes. Cutting a new opening in a foundation is structural work. Cities such as Prior Lake ask for a site plan, a wall elevation and a section showing the header size, sill height and well depth, then inspect the framing and the final. Call Gopher State One Call before digging.
Is a closet required for a room to count as a bedroom in Minnesota?
The building code does not require one. The Minnesota Residential Code's sleeping-room rules cover the escape opening, 70 sq ft of floor area with no dimension under 7 ft, ceiling height, heat and alarms. Whether a room without a closet is listed or appraised as a bedroom is a real-estate question, so ask your agent.
Is a casement or slider better for a basement egress window?
A casement. Its sash swings fully open, so nearly the whole frame becomes clear opening. A slider only opens half its width, so it needs a frame roughly twice as wide to reach the same clear area. A hopper or awning window tilts into the escape path and is a poor choice for egress.
Sources (11)
- City of Saint Paul DSI: Emergency Escape and Rescue Openings handout (2020 Minnesota Residential Code, R310) — R310 numbers: 5.7 / 5.0 sq ft, 24 in height, 20 in width, 44 in sill; operation without keys or tools, ASTM F2090; well 9 sq ft and 36 in; ladder over 44 in deep, 12 in, 3 in, 18 in, 6 in encroachment; drainage R310.2.3.2; deck 36 in path; replacement windows R310.2.5; sprinkler exception; 821 sq in; casement 9 sq ft clear; guardrail recommendation
- Minn. R. 1309.0310, Section R310 Emergency Escape and Rescue Openings (Office of the Revisor of Statutes) — Minnesota amendments to R310: each basement sleeping room, sprinkler and mechanical-only exceptions, licensed foster and day care minimums, R310.6 and R310.6.1 for existing basements
- Minn. R. 1309.0310, Emergency Escape and Rescue Openings (Cornell LII) — Text of Minn. R. 1309.0310 confirming the basement sleeping-room and new-sleeping-room rules
- Minnesota Rules chapter 1309, Minnesota Residential Code (Minnesota DLI, full chapter PDF) — Minnesota Residential Code adopts the 2018 IRC; R305.1 7 ft and R305.2.1 6 ft 4 in for existing basements; R314 and R315 amendments for existing areas; R315.3 CO within 10 ft
- City of Prior Lake: Egress windows handout — Grade-floor 5 sq ft definition, covers allowed if clear opening meets egress, U-factor 0.32, 5 ft setback and easements, permit drawings incl. header section, inspections, Gopher State One Call
- City of Savage: Finished basement handout — Grade-floor definition, ladder over 44 in, smoke alarms throughout house when finishing a basement, hardwired and interconnected in new areas, CO within 10 ft, ceiling heights
- City of Saint Paul DSI: Basement finish handout — R304 70 sq ft and 7 ft, R303.10 heat to 68 F, R314.3 smoke alarm locations, CO within 10 ft, fuel-burning appliances not in bedrooms
- City of Chanhassen Inspections Division: Finishing basements handout — Egress sill and 5.0 sq ft opening, smoke alarms on all levels and every sleeping room including existing areas, separate permits
- Anne Arundel County: Finished basement code requirements (2021 IRC summary) — Confirms IRC R304 70 sq ft minimum area and 7 ft minimum horizontal dimension
- Basement Systems: Egress window well (RockWell) — Opening cut with a masonry saw; well flanges sealed and fastened to the foundation; built-in steps in egress wells
- Basement Systems: Window well drain (WellDuct) — Water pooling in a window well can leak around the window opening
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Keep reading
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- Do I need a permit to finish my basement in Minnesota?
- How should I lay out my finished basement?
- Can I put a kitchenette in my basement guest or in-law suite?
- What should you do with the mechanical room when you finish a basement?