Egress Window Code Requirements in Michigan
Every number an inspector will check, what each one actually measures, and the local overlays that catch Grand Rapids homeowners by surprise. Written to be read with a tape measure in your hand.
The opening: 5.7 square feet, and why it isn't 20×24
Michigan Residential Code Section R310 governs emergency escape and rescue openings — the code's formal name for what everyone calls an egress window. The headline requirement is a net clear opening of not less than 5.7 square feet. For grade-floor openings and below-grade openings, that figure drops to 5.0 square feet, which is the number that applies to most basement installations in Grand Rapids.
Alongside the area requirement sit two dimensional floors: the opening must be at least 24 inches high and at least 20 inches wide. These are minimums that must be satisfied in addition to the area, not instead of it. A window measuring exactly 20 by 24 inches yields 3.3 square feet and fails, even though it technically clears both dimensional minimums. To reach 5.7 square feet you need something closer to 20 inches by 41 inches, or 24 inches by 34 inches, or any pairing that multiplies past about 820 square inches.
Net clear opening is the free, unobstructed space that exists when the window is fully open — the hole a firefighter in gear has to get through, and the hole an occupant has to get out through. It is not the rough opening you cut in the wall, not the outside frame dimension, and not the glass area. On a double-hung or a horizontal slider, only the operable half counts, which is why those styles rarely work as basement egress without going very large.
That last point drives window selection more than anything else. A casement window swings the entire sash clear of the opening, so nearly the whole frame counts toward net clear opening — which is why casements dominate basement egress work. A slider gives you roughly half. A double-hung gives you roughly half, and the sash that remains eats into the height. Sizing a double-hung to hit 5.7 square feet of net clear opening means buying a very large window and cutting a very large hole.
Sill height: the 44-inch rule
The bottom of the clear opening cannot sit more than 44 inches above the finished floor. Note the wording: finished floor. If you are planning to put down two inches of subfloor and flooring in that basement, measure from where the floor will end up, not the bare slab.
This rule is the one that most often forces a bigger excavation than homeowners expect. In a typical Grand Rapids basement with roughly seven and a half feet of head height, an existing window sits high in the wall — often 60 to 70 inches up. Bringing the sill down to 44 inches means the new opening extends well below existing grade outside, which is precisely why the window well requirements exist and why the outside dig is a real part of the job.
Window wells, ladders and rung spacing
When the bottom of the opening sits below the adjacent ground level, the code requires a window well. Three numbers govern it:
- Minimum 9 square feet of horizontal area.
- Minimum 36 inches of horizontal projection away from the foundation.
- Minimum 36 inches of width.
Those figures interact: a well that projects exactly 36 inches and spans exactly 36 inches gives you 9 square feet on the nose. Go narrower in one direction and you have to go longer in the other. In practice, a compliant egress well for a wide casement usually runs somewhere around 40 to 60 inches across the face.
The well also cannot obstruct the window. A well ladder, steps, or a cover that blocks the sash from swinging fully open defeats the whole opening — inspectors check this by operating the window, not by reading a spec sheet.
Where the well is deeper than 44 inches, permanent steps or a ladder are required, and the code is specific about them: rungs spaced not more than 18 inches apart, an inside width of at least 12 inches, and a projection of at least 3 inches from the wall. The ladder must remain usable and must not impede the window's full opening. Our window wells page covers material choices and the drainage detail that keeps a well from becoming a cistern.
Where an egress opening is required
The rule is broader than most people assume. Basements, habitable attics and every sleeping room require at least one operable emergency escape and rescue opening. Where a basement contains more than one sleeping room, each sleeping room needs its own opening — a single shared window at the bottom of the stairs does not cover two bedrooms.
There is a narrow exception: storm shelters, and basements used only to house mechanical equipment where the total floor area does not exceed 200 square feet. An unfinished basement holding nothing but a furnace and a water heater is not the target of this rule. The moment you finish that space into habitable rooms, it is.
This is also why the requirement follows renovation rather than just new construction. Adding a sleeping room to an existing house — including in a basement that has stood there since 1955 — triggers the requirement for that room. Existing conditions are grandfathered only until you change them.
Operation, obstructions and what the window opens onto
Three requirements get overlooked because they are not numbers:
- The opening must be operable from the inside without keys, tools or special knowledge. A window that requires you to remove a screw, lift out a storm panel, or know a trick is not compliant. Window opening control devices meeting the relevant ASTM standard are permitted.
- The opening must open directly into a public way, or a yard or court that opens to a public way. A window that dumps into a fully enclosed courtyard with no route out does not satisfy the intent.
- Bars, grilles, grates and covers are allowed only if they release from the inside without keys, tools or force greater than what the code permits — and only if the opening still meets its minimums with them in place.
Light and ventilation are a separate test
Passing R310 does not automatically make a basement room a legal bedroom. Habitable rooms also have to satisfy natural light and ventilation requirements — generally a glazed area of at least 8 percent of the room's floor area, with an openable area of at least 4 percent. For a 120-square-foot basement bedroom that means roughly 9.6 square feet of glass. Ceiling height is a third test; finished basement living space generally needs about 7 feet of clear height.
The good news is that a properly sized egress casement usually satisfies all three at once. The bad news is that a room can pass egress and still fail as a bedroom on ceiling height or floor area, which we walk through on the basement bedroom page.
Grand Rapids and Kent County overlays
State code is the floor. Local administration is where projects actually stall.
Permits are mandatory. Cutting a foundation wall for an egress window requires a building permit in the City of Grand Rapids. Residential permit applications run through the Development Center at 1120 Monroe Ave NW, and plans have to be uploaded before plan review begins.
Historic districts add a step. Grand Rapids has several locally designated historic districts, Heritage Hill among the largest urban historic districts in the country. Inside one, a Certificate of Appropriateness from the Historic Preservation Commission has to be issued before Building Safety Services will issue the permit — commonly four to six additional weeks. Since an egress window changes an exterior elevation, it is squarely the kind of alteration that gets reviewed.
Different counters in different townships. Ada and Cascade Townships handle building permits through the Kent County Building Department. East Grand Rapids has designated Cascade Township's building inspection services as its building official. Same state code, different desk and different lead time.
Rentals face a second code. Non-owner-occupied properties in Grand Rapids are inspected under the Rental Certification Program against the city's property maintenance code, which was updated to the 2021 International Property Maintenance Code effective January 1, 2024. That inspection is separate from a building permit and applies whether or not you have recently renovated. See our rental property egress page.
One honest caveat. Code editions change, and municipalities amend them. Everything above reflects Michigan Residential Code R310 as we understand it at the time of writing, and it is meant to help you have an informed conversation — not to substitute for your building department's ruling on your specific house. Before you buy a window or sign a contract, confirm the current requirements with the jurisdiction that will inspect the work. We do that as a matter of course on every job we quote.
My basement bedroom has been there for 30 years. Am I grandfathered?
Possibly, for as long as nothing changes. Existing non-conforming conditions are often tolerated until work is done, the property is sold, or a rental inspection occurs. What is not grandfathered is a room finished without a permit — that was never legal, so there is nothing to grandfather. Appraisers and inspectors routinely decline to count a basement room as a bedroom without compliant egress, which is where the financial consequence usually shows up.
Does a walkout door count instead of a window?
Yes. The code requires an emergency escape and rescue opening, and a door that opens directly to the outside satisfies it for the room it serves. The catch is the phrase "for the room it serves." A walkout slider in the family room does not provide egress for a bedroom down the hall with its own door — that bedroom still needs its own opening.
Can the window well cover stay on?
Yes, provided it is releasable from inside the well without keys, tools or special knowledge, and it does not reduce the opening below the minimums. A cover that latches from the outside, or a heavy grate a child cannot lift, is a problem. We size covers to the well and specify releasable hardware for exactly this reason — details on our window well covers page.
Is 5.7 or 5.0 square feet the number for my basement?
For a below-grade basement opening, the reduced 5.0 square foot figure generally applies. We design to 5.7 anyway wherever the wall allows it, because the margin costs almost nothing at the point of cutting and it removes any argument at inspection. Ask your inspector which figure they will apply before ordering.
Who measures the net clear opening — me or the inspector?
The inspector, with the window open. Manufacturer literature usually lists net clear opening for each unit size, but it lists it for the window alone. Once a window is set in a buck inside a masonry opening, trim and framing can shave usable inches. We measure the installed opening and hand you the figure in writing at completion.
Have someone measure it before you buy a window
We'll measure your existing opening against every R310 requirement, tell you plainly whether it passes, and price the fix if it doesn't. No charge for the visit.