Egress Window Check
Clear opening area, minimum width and height, sill height, and the window well you need for a bedroom in a basement, with what to change when it fails.
A 36 in x 24 in opening is 6.0 sq ft, which passes 5.7. A 24 x 24 opening is 4.0 sq ft and fails on area, not width. Basements count for the 44 in sill limit, and a window well over 44 in deep needs a ladder or a grate.
How the math works
- Area (IRC R310.2): the emergency-rescue opening must give a net clear opening of 5.7 sq ft, and the net measurement is the clear space with the sash in the open position, not the frame and not the glass.
- Width and height (R310.2): a net clear width of 20 in and a net clear height of 24 in, each measured with the window open, and the opening must be operable from the inside without a key, tool, or separate fastening.
- Sill height (R310.2): the sill must sit no higher than 44 in above the finished floor. A permanent step, platform, or fixed seat under the opening counts, and it must be at least 16 in wide by 36 in deep at the opening.
- Window wells (R314.3): an opening below grade needs a well with a horizontal projection of 36 in and 9 sq ft of projection area, a depth of 44 in max, and a ladder or grate when the well is deeper than 44 in. A grate over 44 in deep must open from the escape side without a key.
- Basement bedrooms (R310.1): every sleeping room needs an escape opening on the exterior side of the room, and the escape route must reach grade, a yard, a door to a public way, or a rescue screen at a window well.
What size window meets the 5.7 sq ft egress rule?
A clear opening of 24 in high by 34 in wide gives 5.67 sq ft, which is a hair short, so plan on 24 in by 36 in (6.0 sq ft) or 36 in by 24 in. A double-hung counts only the bottom sash open, so a 36 in wide double-hung at 24 in clear height on the lower sash is the standard egress window.
Does a window well have to be 36 inches?
The horizontal projection is 36 in minimum with 9 sq ft of projection area, and the depth from grade to the bottom is capped at 44 in with a ladder or grate required beyond 44 in. A well that is narrower at the bottom than at the top counts at the top of the well.
Can a basement bedroom window open to the outside at grade?
Yes, and that is the cleanest pass: the well projection stays 36 in and 9 sq ft, the sill under 44 in, and the escape route to a yard, a walk-out, or a public way. A window well that empties into a light well needs the 36 in clear at the sill, not at the bottom.