How the egress opening check works
Measure the net clear opening produced by normal operation of the window: the open space a person climbs through, not the frame, the sash or the rough opening. Everything else is multiplication and comparison:
- Net clear area in square feet = clear width (in) × clear height (in) ÷ 144, since a square foot is 12 × 12 = 144 square inches.
- Clear height needed at a given width = required area × 144 ÷ width, but never less than the 24 in minimum height.
- An opening is a grade-floor opening when the bottom of its clear opening is no more than 44 in above or below the finished ground next to it. Grade-floor openings may use the smaller 5 sq ft area; every other opening needs 5.7 sq ft. That includes a basement opening more than 44 in below grade. The 2018 IRC exception named grade-floor and below-grade openings; the exception in R310.2.1 (2021) and R319.2.1 (2024) names grade-floor openings only, so a deeper below-grade opening needs 5.7 sq ft in both editions. The tool says so in its result when it applies.
- Area well horizontal area in square feet = projection out from the wall (in) × width along the wall (in) ÷ 144.
- Each limit is its own comparison: area, height, width, well area, well projection and well width must reach their minimums, and the floor-to-opening height must not exceed its maximum.
These are arithmetic steps, not code text. The limit values and section numbers are cited so you can find them in your own code book; read the full sections there, including their exceptions.
Which sections, in which edition
The 2024 IRC reorganized Chapter 3. Emergency escape and rescue openings moved from Section R310 to Section R319, keeping the same subsection pattern. The base dimensional limits used here did not change. Tab the right numbers for the edition you will bring to the exam.
- Where an opening is required (basements, habitable attics, sleeping rooms): R310.1 in the 2021 IRC, R319.1 in the 2024 IRC.
- Minimum net clear area and the grade-floor exception: R310.2.1 and R319.2.1.
- Minimum clear height and width: R310.2.2 and R319.2.2.
- Maximum height of the bottom of the clear opening above the floor: R310.2.3 and R319.2.3.
- Openings under decks, porches and cantilevers: R310.2.4 and R319.2.4.
- Area wells: R310.4 and R319.4; well size R310.4.1 and R319.4.1; ladder or steps R310.4.2 and R319.4.2.
Worked example: a 20 in wide casement
A second-floor bedroom casement opens to a clear width of 20 in and a clear height of 41 in, with the bottom of the opening 24 in above the floor.
- Net clear area: 20 × 41 ÷ 144 = 820 ÷ 144 = 5.694 sq ft.
- The opening is well above grade, so the general 5.7 sq ft minimum applies. 5.694 is 0.006 sq ft short, so it fails in both editions even though width (20 in) and height (41 in) each meet their minimums.
- Height needed at 20 in wide: 5.7 × 144 ÷ 20 = 41.04 in. A unit with at least 41 1/16 in of clear height passes.
- The same 20 × 41 opening on a grade-floor wall, with its bottom 30 in above the ground outside, needs only 5 sq ft and passes with 0.694 sq ft to spare.
Worked example: a basement opening with an area well
A basement bedroom window opens to 24 in wide by 36 in high. The bottom of the clear opening is 40 in above the basement floor and 36 in below the finished grade outside. The well projects 36 in from the wall, is 40 in wide and is 50 in deep.
- Net clear area: 24 × 36 ÷ 144 = 864 ÷ 144 = 6.0 sq ft. The bottom of the opening is 36 in below grade, within 44 in, so it is a grade-floor opening with a 5 sq ft minimum. It would also meet the general 5.7 sq ft.
- Height 36 in and width 24 in meet the 24 in and 20 in minimums. The 40 in floor-to-opening height is under the 44 in maximum.
- The opening is below grade, so it needs an area well. Well area: 36 × 40 ÷ 144 = 1,440 ÷ 144 = 10.0 sq ft, over the 9 sq ft minimum, and both well dimensions reach 36 in.
- The well is 50 in deep, more than 44 in, so it needs a permanently fixed ladder or steps that the open window does not block.
These are original examples, not exam questions.
What this tool does not check
It assumes a single window with a rectangular clear opening measured in its normal open position. It does not check emergency escape doors, opening control and fall prevention device heights, bars, grilles and covers, replacement-window and existing-building provisions, ladder and step dimensions, well drainage, or the clear path required under decks and porches (36 in, R310.2.4 and R319.2.4). A ladder or steps may encroach into the well dimensions within limits set in the well-size section; this tool does not adjust for that. Check those items in your own code book and with the AHJ.
Egress openings on the B1 exam
Emergency escape and rescue openings fall under the public-safety content area of the ICC Residential Building Inspector (B1) outline; the B1 exam outline guide breaks that area down. Questions usually test whether you can find the right section fast in an open-book setting, so practice locating each limit in your edition rather than memorizing it. The IRC stair check covers the other public-safety geometry topic the same way, and the B1 practice page has the free 10-question check.