An egress window, or in code language an emergency escape and rescue opening, is the window a person can climb out of, and a firefighter climb in through, when the door is blocked. The International Residential Code (IRC) requires one in every bedroom and in basements and habitable attics, and it sets a minimum opening area, height, width and sill height. This guide summarises those rules, gives the smallest window openings that pass, and has a quick checker for your own window.
Check a window
Enter the opening the window gives when it is fully open, measured between the stops or sash edges, not the size of the frame. For a double-hung or single-hung window that is only the part below the raised sash; for a casement it is the opening beside the swung-out sash, which can be reduced by the hinge hardware.
Egress window requirements (IRC 2021)
| Item | Requirement | IRC section |
|---|---|---|
| Where required | Every basement, every habitable attic and every sleeping room needs at least one emergency escape and rescue opening; a basement with sleeping rooms needs one in each sleeping room | R310.1 |
| Exception | Basements used only for mechanical equipment and not more than 200 sq ft | R310.1 |
| Opens to | A public way, or a yard or court that leads to one | R310.1 |
| Minimum net clear opening | 5.7 sq ft; 5.0 sq ft for a grade-floor or below-grade opening | R310.2.1 |
| Minimum clear height and width | 24 in high and 20 in wide, both at the same time as the area minimum | R310.2.1 |
| Operation | Opens from inside without keys, tools or special knowledge | R310.1, R310.2.1 |
| Maximum sill height | 44 in from the floor to the bottom of the clear opening | R310.2.2 |
| Window well size | At least 9 sq ft of horizontal area, with at least 36 in of projection and 36 in of width | R310.2.3 |
| Window well ladder | Required when the well is deeper than 44 in: at least 12 in wide inside, rungs projecting at least 3 in, spaced no more than 18 in apart vertically | R310.2.3.1 |
| Under a deck or porch | Allowed if the window opens fully and there is a path at least 36 in high to a yard or court | R310.2.4 |
| Replacement windows | May be exempt from the size and sill rules if the new window is the same or a larger-opening operating style and does not reduce the existing clear opening | R310.2.5 |
Egress window size chart: smallest clear opening that passes
| Clear width | Height for 5.7 sq ft | Area (sq ft) | Height for 5.0 sq ft (grade floor or basement) | Area (sq ft) |
|---|---|---|---|---|
| 20 in | 42 in | 5.83 | 36 in | 5.00 |
| 22 in | 38 in | 5.81 | 33 in | 5.04 |
| 24 in | 35 in | 5.83 | 30 in | 5.00 |
| 26 in | 32 in | 5.78 | 28 in | 5.06 |
| 28 in | 30 in | 5.83 | 26 in | 5.06 |
| 30 in | 28 in | 5.83 | 24 in | 5.00 |
| 32 in | 26 in | 5.78 | 24 in | 5.33 |
| 34 in | 25 in | 5.90 | 24 in | 5.67 |
| 36 in | 24 in | 6.00 | 24 in | 6.00 |
| 38 in | 24 in | 6.33 | 24 in | 6.33 |
| 40 in | 24 in | 6.67 | 24 in | 6.67 |
Two things stand out. First, the 24 x 20 in minimums alone give only 3.3 sq ft, so a window that is just 24 in high must be about 34-1/2 in wide, and one that is just 20 in wide must be about 41 in high, to reach 5.7 sq ft. Second, because only part of a hung window opens, the window unit has to be much bigger than the clear opening. A double-hung unit often needs to be roughly twice the required clear height, which is why casement and sliding windows are popular for basement egress. Window makers publish the net clear opening of each size; look for it in the product data rather than estimating.
Basement egress and window wells
- Opening area: a basement window whose sill is below the outside grade is a below-grade opening, so the 5.0 sq ft minimum applies (R310.2.1), but the 24 in height and 20 in width minimums still apply.
- Sill height: the 44 in maximum is measured inside, from the basement floor. A built-in step or platform is sometimes accepted to meet it; ask your building department, as rules on this vary.
- Well size: at least 9 sq ft, and at least 36 in out from the wall and 36 in wide (R310.2.3). A 36 x 36 in well is exactly 9 sq ft. The well must also let the window open fully.
- Ladder: wells deeper than 44 in need a permanently fixed ladder or steps (R310.2.3.1). The ladder may encroach up to 6 in into the required well dimensions (R310.2.3), and must not stop the window from opening fully.
- Drainage: window wells need drainage to the foundation drain or another approved method (R310.2.3.2), unless the soil drains well.
- Covers: a cover or grate over a well must be removable from inside without tools or special effort.
Bedrooms on upper floors: fall protection
An upstairs egress window has to be low enough to climb out of, but a low window high above the ground is also a fall hazard for children. The IRC handles this separately (R312.2): where the sill is less than 24 in above the floor and the window is more than 72 in above the ground outside, the opening must be limited or fitted with a window opening control device. Those devices have to release so the window still works for emergency escape. Check both rules when you choose a sill height.
Frequently asked questions
What size does an egress window need to be?
The clear opening must be at least 5.7 sq ft (5.0 sq ft at grade floor or in a basement), at least 24 in high and 20 in wide, with the sill no more than 44 in above the floor (IRC R310.2.1, R310.2.2).
Does a basement bedroom need an egress window?
Yes. The IRC requires an emergency escape and rescue opening in every sleeping room, including basement bedrooms (R310.1). An exterior door that opens directly outside can serve instead in some layouts.
How big does an egress window well need to be?
At least 9 sq ft of floor area, at least 36 in out from the wall and 36 in wide, with a ladder or steps if it is more than 44 in deep (R310.2.3, R310.2.3.1).
Can a double-hung window be an egress window?
Yes, if the opening below the raised sash meets the area, height and width minimums. Because only half the window opens, the unit itself needs to be large, so check the maker’s net clear opening figure.
Do replacement windows have to meet egress size?
Not always. The IRC exempts replacement windows from the size and sill rules when the new window is the same or a larger-opening style and does not make the clear opening smaller (R310.2.5). Local rules can be stricter.
Sources
- International Code Council, 2021 International Residential Code (IRC). Requirements are paraphrased with their section numbers; local codes and amendments may differ, so confirm with your building department.
- Window opening control devices: ASTM F2090, as referenced by IRC R312.2 (not reproduced).
Last reviewed: 24 October 2026. Numbers in the tables are our arithmetic from the sources listed; code sections are summarised, not quoted. How we check our work: methodology and corrections. Spotted an error? Please let us know.