An egress window, called an emergency escape and rescue opening in 2021 IRC Section R310, needs a net clear opening of at least 5.7 square feet, at least 24 inches high and 20 inches wide, with the bottom of the opening no more than 44 inches above the floor. Grade-floor openings may be 5 square feet.
An egress window is an operable window or door that lets someone leave a bedroom or basement, and lets a firefighter get in, without keys, tools, or special knowledge. The 2021 International Residential Code (IRC) sets the size, height, and well rules. The adopted code edition and your local amendments govern, so confirm them with your building department before you frame.
Key facts
- The net clear opening must be at least 5.7 square feet, or 5 square feet at grade-floor openings (2021 IRC Section R310.2.1).
- The net clear opening must be at least 24 inches high and at least 20 inches wide, measured as the result of normal operation (2021 IRC Section R310.2.2).
- The bottom of the clear opening must be no more than 44 inches above the floor (2021 IRC Section R310.2.3).
- An area well must have at least 9 square feet of horizontal area, with a projection and width of at least 36 inches (2021 IRC Section R310.4.1).
- Area wells deeper than 44 inches need an approved, permanently affixed ladder or steps (2021 IRC Section R310.4.2).
- Where a door serves as the opening, it must be side-hinged or sliding (2021 IRC Section R310.3).
Where are egress windows required?
Basements, habitable attics, and every sleeping room need at least one operable emergency escape and rescue opening, with exceptions listed in 2021 IRC Section R310.1. Where a basement contains sleeping rooms, each sleeping room needs its own opening.
The opening has to lead somewhere safe: directly to a public way, or to a yard or court that provides an unobstructed path to a public way. The base IRC text gives a minimum width of 36 inches for that yard or court. Two exceptions matter for planning: basements used only for mechanical equipment up to a stated floor area, and sprinklered dwellings where a basement has a complying means of egress. Read the exact wording of the adopted code, because these exceptions are amended in some jurisdictions.
Section R310.1.1 adds an operating rule. The opening must work from inside without keys, tools, or special knowledge. Window opening control devices and fall prevention devices that comply with ASTM F2090 are allowed, and they must be no more than 70 inches above the finished floor.
How big does an egress window need to be?
The net clear opening must be at least 5.7 square feet, at least 24 inches high, and at least 20 inches wide, all measured with the window operated normally.
2021 IRC Section R310.2 summary: net clear opening of an operable egress window.
| Requirement | Value | 2021 IRC section |
|---|---|---|
| Minimum net clear opening area | 5.7 sq ft | R310.2.1 |
| Minimum area, grade-floor opening | 5 sq ft | R310.2.1 exception |
| Minimum clear height | 24 in. | R310.2.2 |
| Minimum clear width | 20 in. | R310.2.2 |
| Maximum height of clear opening above floor | 44 in. | R310.2.3 |
The area rule and the two dimension rules are separate tests, and you must pass all three. A window that is exactly 24 inches high and 20 inches wide in the clear does not reach the area minimum, so at least one dimension has to be larger. Choose the size from the manufacturer's published net clear opening, not from the nominal window size.
Why net clear opening is smaller than the window
Net clear opening is the open space left after the sash is moved to its normal open position. The frame, the sash, and the hardware all take away from the rough opening, and the operating style changes how much is lost. The code ties the dimensions to normal operation, so a window that only reaches the minimum with its sash removed does not count.
Manufacturers publish the net clear opening and the rough opening for each model. Use those two figures together: the first proves code compliance and the second tells you how to frame the wall.
How do you frame the rough opening for an egress window?
Frame the rough opening to the manufacturer's stated size, and set the sill so the bottom of the clear opening lands at or below 44 inches above the finished floor.
The sill height you frame is not the same as the height the code measures. The code measures to the bottom of the clear opening, which sits higher than the rough sill by the thickness of the sill framing, the window frame, and the sash rail. Work from the manufacturer's installation drawing and check the finished measurement before you cut cripples.
Three framing decisions follow from the size:
- Opening width. Egress sizes usually call for a wide rough opening, such as a double casement or a large slider. A wide opening in a bearing wall needs a larger header and often more jack studs. See the header size chart for how span, building width, and snow load set the header, and use an engineered header where the sawn-lumber tables run out.
- Header height. A tall clear height pushes the header up and shortens the cripple studs above it. Wall framing basics covers how king, jack, and cripple studs fit together.
- Sill height. A high sill leaves a short cripple wall below the window but can fail the 44 inch limit, so set it from the manufacturer's drawing.
The framing around the opening carries load like any other opening in the wall, so the usual stud layout in stud spacing applies on either side.
What are the basement egress window requirements?
A basement egress window needs the same size as any other egress opening, plus an area well when the clear opening sits below adjacent grade.
2021 IRC Section R310.4 requires the well to have at least 9 square feet of horizontal area with a projection and width of at least 36 inches. The size must also let the window open fully. The ladder or steps required for deep wells may encroach up to 6 inches into the well dimensions.
The rough opening in a basement wall usually sits in a concrete or masonry foundation wall, and the support over it comes from the foundation design, not from the wood header tables in the wall framing chapter. The egress rules set the opening size; the wall construction sets how it is carried.
What are the window well requirements?
A window well, which the code calls an area well, must be big enough to open the window fully, drain properly, and let a person climb out.
| Window well item | Requirement | 2021 IRC section |
|---|---|---|
| Horizontal area | At least 9 sq ft | R310.4.1 |
| Projection and width | At least 36 in. | R310.4.1 |
| Ladder or steps required | Depth over 44 in. | R310.4.2 |
| Ladder inside width | At least 12 in. | R310.4.2.1 |
| Ladder projection from wall | At least 3 in. | R310.4.2.1 |
| Ladder rung spacing | At most 18 in. on center | R310.4.2.1 |
| Step tread depth | At least 5 in. | R310.4.2.2 |
| Step riser height | At most 18 in. | R310.4.2.2 |
Drainage is a separate requirement. Section R310.4.3 says area wells connect to the foundation drainage system required by Section R405.1, with an exception for well-drained soils described in Table R405.1.
Covers and grilles are allowed, but Section R310.4.4 requires the net clear opening to still meet the size rules, and the device must release from inside without a key, tool, or excessive force.
How do you show an egress window on a framing plan?
Mark the window on the plan view as an opening with its rough opening dimension, a header callout, and a note that it is an egress window.
A reviewer should be able to check four things from the drawing: the rough opening width, the header size or product, the sill height above the floor, and the model or net clear opening it was based on. Label the window with a tag, such as EGR, and add a legend entry; framing plan symbols shows how to build a consistent legend. Basement windows also need the well shown outside the wall in plan view with its width and projection. For how reviewers read these notes, see how to read a floor framing plan.
Framing Plan draws walls, openings, beams, and joist layouts, and exports PNG, PDF, and DXF. It does not check egress sizes or code compliance, and its editor works in millimeters with a bundled sample profile of demo figures. Treat the egress callouts as notes you type from the code and the manufacturer's data.
Summary
Under 2021 IRC Section R310, an egress window needs a net clear opening of at least 5.7 square feet (5 square feet at grade floor), at least 24 inches high and 20 inches wide, with the clear opening no more than 44 inches above the floor. Below-grade openings need an area well of at least 9 square feet and 36 inches in projection and width. Frame the rough opening from the manufacturer's data and size the header for the span.
Lay out the opening, header, and well on a preliminary drawing in the Framing Plan studio, then confirm the details against the adopted code and the window manufacturer's instructions.