Egress Windows in St. Louis

What the code asks of a bedroom or basement escape window, when replacing one brings the rule into play, and how to know before ordering whether the window you want will actually pass.

Get a free estimate →Read the guide

Net clear opening measured on every bedroom window
Basement rules checked against your city's edition
Casement hinge and clear width confirmed first

Free written estimateRot priced before you sign

Permit & code looked upFor every city we work in

Windows and siding togetherOne wall, opened once

Both sides of the river45 cities & counties

The code's name for it is an emergency escape and rescue opening, and both halves count. It is how someone gets out of a bedroom when the hallway is full of smoke, and how a firefighter in full gear gets in. The rule is Section R310 of the International Residential Code, and each city here enforces its own edition: unincorporated St. Louis County the 2015, the City of St. Louis the 2018, Kirkwood the 2021. The figures on this page come from the 2015 and 2018 text; your town's page names its edition.

Our window buying guide lists the numbers. This page is about using them on a real house: how to measure, when a replacement has to comply, what changes in a basement, and why the style of window decides most of it.

Which rooms need an escape opening

Under R310.1, every sleeping room needs at least one operable escape opening, and so do basements and habitable attics. A basement with bedrooms needs one in each bedroom. The only basement left out is one used just for mechanical equipment, up to 200 square feet. The opening has to lead straight outside, to a public way or to a yard or court that reaches one.

It does not have to be a window. A side-hinged door or a slider to the outside also counts; below grade it needs a bulkhead or area well, depending on the edition. Opening control devices are allowed on an escape window if they meet ASTM F2090, and the window must still open from inside without keys, tools or special knowledge (R310.1.1).

The 2018 edition added one more way out for basements: in a house with an automatic sprinkler system, a basement bedroom can go without its own opening if the basement has two code-compliant exits, or one exit plus an escape opening. The 2015 edition, which the County still enforces, has no such exception.

The numbers, and how to measure them

Everything in R310.2 is net clear opening: the hole you can climb through with the window opened the normal way from inside. Not the glass size, not the frame, not the rough opening. The minimums: 5.7 square feet of clear area, or 5.0 for a grade-floor or below-grade opening; a clear height of 24 inches; a clear width of 20 inches. The sill can sit no higher than 44 inches off the floor.

The catch most people miss: the two minimum dimensions multiply out to only 480 square inches, about 3.3 square feet. To reach 5.7, an opening exactly 24 inches tall must be 34.2 inches wide, and one exactly 20 inches wide must be 41 inches tall. For a 5.0 grade-floor opening, those become 30 and 36 inches.

A grade-floor opening, by the code's definition, is one whose sill sits within 44 inches above or below the finished ground outside it. On a double-hung, clear height runs from the sill to the bottom of the raised lower sash. On a casement, clear width is what the hinge and operator arms leave you.

Not the rough opening. A window can fill a 3-by-5 hole and still fail. The number that matters is the one you get with the sash open.

Why a replacement double-hung usually falls short

A double-hung opens only its lower half, and the meeting rail and frame take a share of that. One window maker's published opening table shows how tight it gets. Its double-hung with a frame of about 35½ by 59½ inches, a 3-by-5-foot window, opens to 5.378 square feet: 31.9 inches wide by 24.3 inches high. That clears the 24-inch height by a quarter of an inch and passes as a grade-floor opening, but it misses the 5.7 square feet an upper-floor bedroom needs.

Two inches taller, with the sashes split unevenly on purpose, the same line reaches 5.711 square feet, over the line by a hair. That is how small the margins are. Sliders have the same problem turned on its side, since only half the width opens.

So a replacement that drops neatly into the old opening can still fall short of the numbers, which is why we measure bedroom and basement windows before anything is ordered rather than trusting the size printed on the old frame.

Casement windows, and why the hinge matters

A casement swings its whole sash out, so most of its frame becomes clear opening. That is why it is the usual fix when a bedroom window has to pass. The hinge and operator hardware still take width, though, and on a narrow unit that decides the result.

The same maker's casement table shows it. A unit about 27½ inches wide and 47½ tall opens 19.44 inches clear on its standard hinges, under the 20-inch minimum, and 22.02 inches on its optional egress hinges, for 6.71 square feet of clear area. The table also notes that its units taller than about 71 inches hang on butt hinges and do not open a full 90 degrees. Order from the published clear-opening figure for the exact unit and hinge, never from the frame size.

A casement opening into a basement well needs room to swing; the well has to let the window open fully. And switching from a double-hung to a casement can change your permit. Unincorporated Jefferson County ends its exemption when the operating style changes (Imperial), and Town and Country exempts only replacements of the same size and type.

When replacing a window brings the rule in

The code does not force an old bedroom window up to today's size just because you replace it. The 2015 and 2018 editions carry a replacement-window exception (R310.2.5): the new unit is excused from the size and sill height rules if it is the biggest standard size its maker offers that fits the existing frame or rough opening, if it keeps the old operating style or switches to one that opens at least as much, and if the job is not part of a change of occupancy. The 2021 edition keeps a replacement-window section, renumbered R310.5.

Put simply, a replacement may not make the escape worse, but it does not have to make it better. St. Louis County built nearly the same conditions into its permit exemption and requires a permit for any swap to a style with a smaller opening (permit rules by city).

The exception covers replacement only. It does not excuse a new bedroom in an existing basement (R310.6), a bedroom in an addition (R310.5), or a window swapped as part of a change of occupancy. And legal is not the same as easy to get out of. We measure every bedroom and basement window we quote against the full numbers, so you can decide with the facts in front of you whether to keep the old size or change it.

Basement bedrooms and window wells

Under the 2015 and 2018 editions, finishing or repairing a basement does not by itself call for an escape opening (R310.6), but creating a bedroom down there does, and the new bedroom gets the full requirement. The 2021 edition, adopted by Kirkwood, Florissant and several other cities here, eases that for existing basements: an existing operable window with at least 4 square feet of clear opening, 22 inches high and 20 wide, can be accepted. Your city's edition decides which answer you get.

A window whose sill is below the ground outside needs a well (R310.2.3):

At least 9 square feet of floor area, at least 36 inches out from the wall and 36 inches across, and room for the window to open all the way.
Deeper than 44 inches, a permanently attached ladder or steps that work with the window open: rungs at least 12 inches wide, sticking out at least 3 inches, spaced no more than 18 inches apart. The ladder may take up to 6 inches of the well.
Drainage into the foundation drain or another approved method, unless the soil is the well-drained kind the code exempts.
Any grate, cover or bars that release from inside without a key, a tool, special knowledge or extra force (R310.4).

When the opening itself has to get bigger

If no window that fits the existing hole can pass, the hole has to change, and the job stops being a window replacement. In a framed wall that can mean a new header and reframing. In a basement it means cutting the foundation wall, supporting the new opening, then excavating, draining and lining a well. That is structural and excavation work, and every city or county here that publishes a rule requires a permit to enlarge an opening or cut a new one (permits by city). In a City of St. Louis historic district, a changed opening goes through the Cultural Resources Office as well (historic district rules).

What we can give you is the target: the clear opening the room needs, and the window that satisfies it once the opening is the right size, so whoever does the structural work builds to the right number the first time.

What we check before an egress window is ordered

On every bedroom and basement window in the quote, before anything is ordered:

Clear width and height with the sash fully open, measured from inside, and the area they make.
Sill height from the finished floor, and how far the sill sits above or below the ground outside, which decides whether 5.0 or 5.7 square feet applies.
For a below-grade window: the well's size and depth, its ladder, its drain and its cover.
Anything in the way, such as bars, or a deck or porch overhead, which needs a path at least 36 inches high out from under it.
The maker's published clear-opening figure for the exact replacement unit and hinge.
Your city's code edition and its permit rule for changing styles.

All of it is part of the free estimate, so the choice between a like-for-like swap and a window that passes is yours to make with the numbers in hand.

Common questions about egress windows in St. Louis

Does every bedroom window have to be an egress window?

No. The code asks for at least one escape opening per sleeping room, not every window. A bedroom with three windows needs only one that meets the size and sill rules, and a side-hinged or sliding door straight to the outside can do the job instead.

Do I have to enlarge small bedroom windows when I replace them?

Not under the replacement-window exception in the editions most cities here use, as long as the new window is the largest standard size that fits the opening and opens at least as much as the old one. The exception does not cover a new basement bedroom, a bedroom in an addition, or a change of occupancy, and nothing stops you from choosing a window that passes anyway.

Can a basement bedroom rely on the stairs instead of a window?

Not under the 2015 edition that St. Louis County enforces. The 2018 and 2021 editions allow it only in a house with an automatic sprinkler system, and only if the basement has two code-compliant exits or one exit plus an escape opening. Otherwise each basement bedroom needs its own opening.

What counts as a grade-floor opening?

One whose sill sits no more than 44 inches above or below the finished ground outside it. Those openings need 5.0 square feet of clear area instead of 5.7, which is why a basement window close to ground level can qualify for the smaller number while a second-floor bedroom window usually needs the full 5.7.

Are window well covers and security bars allowed over an egress window?

Yes, as long as they open or come off from inside without a key, a tool, special knowledge or more force than it takes to open the window itself, and the clear opening stays at full size with them in place. That rule is Section R310.4 of the residential code.

Where we work

Egress windows across greater St. Louis, from the city and St. Louis County out to St. Charles, Jefferson and Franklin Counties and across the river into the Metro East. Each city has its own page with the permit rule and code edition that apply there: