Every bedroom needs an emergency escape and rescue opening, usually a window. Under the 2021 International Residential Code (R310), its clear opening, measured with the window opened the normal way, must be at least 5.7 sq ft (5 sq ft on a grade floor), at least 24 in high and 20 in wide, and its bottom no more than 44 in above the floor. A window below the ground outside needs a well of at least 9 sq ft, 36 in each way, with a ladder or steps if it’s deeper than 44 in. Codes are adopted locally, so check with your building department.
Check your window
Open the window the normal way and measure the clear opening: the space you could climb through, between the open sash and the frame.
Checks the minimums in the 2021 IRC, R310.2 and R310.4, as published without amendments. Your city or county may have adopted another edition or changed it. The example values are an Andersen 100 Series 2076 double-hung, whose clear opening is 20 × 41 1/16 in.
Egress window requirements, rule by rule
| Rule | Requirement | 2021 IRC |
|---|---|---|
| Where one is needed | Every sleeping room, every basement and every habitable attic; in a basement, each bedroom needs its own | R310.1 |
| Clear opening | At least 5.7 sq ft; 5 sq ft for a grade-floor opening | R310.2.1 |
| Clear height and width | At least 24 in high and 20 in wide, with the window opened the normal way | R310.2.2 |
| Height from the floor | Bottom of the clear opening no more than 44 in above the floor | R310.2.3 |
| Opening it | From inside, with no keys, tools or special knowledge; window opening control devices (ASTM F2090) no higher than 70 in | R310.1.1 |
| Where it leads | A public way, or a yard or court at least 36 in wide that reaches one | R310.1 |
| Under a deck or porch | The window opens fully, with a path at least 36 in high and 36 in wide to a yard | R310.2.4 |
| A door instead | A side-hinged or sliding door | R310.3 |
| Replacement windows | Exempt from the size rules if the new window is the maker’s largest standard size that fits the existing opening, and the use of the house isn’t changing | R310.5 |
From the 2021 IRC as published without amendments (UpCodes’ copy of Colorado’s 2021 residential code). A grade-floor opening is one whose bottom sits within 44 in above or below the finished ground outside (R202). The 2021 IRC doesn’t define “sleeping room”.
Two traps. Meeting both minimum dimensions isn’t enough: 24 × 20 in is only 3.33 sq ft. And area alone isn’t enough: Andersen’s 100 Series 4046 double-hung opens to 7.02 sq ft, but only 23 1/16 in high, so it fails. The 44 in limit is why a bedroom window can be too high: see minimum bedroom size for the other rules a bedroom has to meet.
Clear opening vs window size
A window has three sizes, and only one counts for egress. Andersen’s charts list them separately:
- Rough opening: the framed hole in the wall, about ½ in bigger than the window each way.
- Window size: the outside of the frame, frame to frame.
- Clear opening: the space between the open sash and the frame, the size you can climb through. This is the egress size.
How much of the frame opens depends on the type:
| Window type | Clear opening | For egress |
|---|---|---|
| Casement | Nearly the whole frame: on Andersen’s 400 Series, about 5.8 in less than the frame’s width and 4.9 in less than its height | The usual pick |
| Double-hung or single-hung | One sash: on Andersen’s 100 Series, about half the frame height less 3.8 in | Needs a tall frame |
| Slider | About half the width: a 20 in clear width takes a slider about 40 in wide (Pella) | Works if wide enough |
| Awning | Opens out from the bottom; Andersen reaches 5.7 sq ft on one size only with the operator detached | Rarely |
| Picture, fixed or glass block | Doesn’t open | Never |
Andersen’s 400 Series casement and 100 Series double-hung charts, and its and Pella’s basement window guides.
Window sizes that meet egress
At a 20 in clear width you need 41.04 in of clear height (5.7 sq ft is 820.8 sq in), and at 24 in wide, 34.2 in. Some real double-hung windows, from Andersen’s 100 Series chart:
| Window | Window size | Clear opening | Area | Egress |
|---|---|---|---|---|
| 2060 | 1 ft 11½ in × 5 ft 11½ in | 20 × 32 1/16 in | 4.45 sq ft | No: too small |
| 2076 | 1 ft 11½ in × 7 ft 5½ in | 20 × 41 1/16 in | 5.70 sq ft | Yes |
| 2660 | 2 ft 5½ in × 5 ft 11½ in | 26 × 32 1/16 in | 5.78 sq ft | Yes |
| 3050 | 2 ft 11½ in × 4 ft 11½ in | 32 × 26 1/16 in | 5.77 sq ft | Yes |
| 4046 | 3 ft 11½ in × 4 ft 5½ in | 44 × 23 1/16 in | 7.02 sq ft | No: under 24 in high |
Andersen 100 Series double-hung spec guide (April 2026), clear opening in the full open position. Other makers and lines differ: use your window’s own clear-opening figures.
A narrow casement doesn’t give its frame width: a 24⅛ in wide Andersen 400 Series casement opens only about 18 in clear, short of 20 in.
Egress window wells
When the bottom of the opening is below the ground outside, the window needs an area well (R310.4):
- Size: at least 9 sq ft of floor, at least 36 in wide and 36 in out from the wall, and big enough for the window to open fully (R310.4.1).
- Ladder or steps: needed when the well is deeper than 44 in. A ladder is at least 12 in wide, 3 in off the wall, with rungs no more than 18 in apart; steps are 12 in wide with 5 in treads and risers up to 18 in. They may take up to 6 in of the well’s size, and the open window must not block them (R310.4.2).
- Drainage: the well drains into the foundation drain system, except on well-drained soils (R310.4.3).
- Covers and grilles: allowed if they open from inside without a key, tool or extra force (R310.4.4).
Steel wells from Shape Products come 42 in, 50 in or 68 in wide, all 36 in out from the wall: 10.5 to 17 sq ft. The ladder is sold separately. Check the well’s inside size, since corrugations and a ladder take some of it.
Questions
What is an egress window?
A window big enough to climb out of in a fire, and for a firefighter to climb in through. The code calls it an emergency escape and rescue opening, and every bedroom needs one.
What size does an egress window need to be?
A clear opening of at least 5.7 sq ft (5 sq ft on a grade floor), at least 24 in high and 20 in wide, measured with the window opened normally, and its bottom no more than 44 in above the floor.
Does a basement need an egress window?
Yes: every basement needs one, and each basement bedroom needs its own. The 2021 IRC exempts storm shelters and basements used only for mechanical equipment up to 200 sq ft, and some sprinklered homes (R310.1).
How deep can a window well be without a ladder?
Up to 44 in. A deeper well needs a permanent ladder or steps (R310.4.2).
Does a replacement window have to meet egress size?
Not if it’s the maker’s largest standard size that fits the existing opening and the house’s use isn’t changing (R310.5). Some local building departments are stricter, so ask yours.
Can a bedroom window be too high?
Yes: if the bottom of its clear opening is more than 44 in above the floor, it doesn’t count as the bedroom’s escape opening (R310.2.3).
Sources
- 2021 International Residential Code, chapter 3, section R310 (UpCodes’ copy of Colorado’s 2021 residential code, adopted without amendments) and chapter 2, definitions: every rule in the tables
- Boulder County, B10: emergency escape and rescue openings: a county handout on the same 2021 rules
- Andersen 100 Series double-hung spec guide (April 2026): clear openings and egress sizes; 400 Series casement and awning size chart: clear opening formulas
- Andersen, how to pick basement windows: the clear opening; casement and gliding windows for egress
- Pella, egress window guide and types of basement windows: sliders about 40 in wide for a 20 in opening; fixed and glass block windows don’t count
- Shape Products steel window well spec sheet and install sheet: well sizes; ladder sold separately
Checked October 20, 2026. Areas, the heights needed for a given width and the checker’s results are our arithmetic from the code’s minimums. This page explains the model code; it isn’t legal or building advice.