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Egress window: what it means on an inspection

Rafter Tie editorial teamUpdated 4 min read

An egress window is an emergency escape and rescue opening, a window or door in a sleeping room or basement that a person can use to get out and a firefighter can use to get in. It has minimum clear area, height and width and a maximum sill height, and it must be usable from the inside in an emergency.

To run a window's numbers against the limits, use the IRC egress window requirements check.

A wall with a window opening and dimension arrows showing a minimum clear height of 24 inches, a minimum clear width of 20 inches and a maximum sill height of 44 inches, with the minimum clear area of 5.7 square feet
Height, width, sill height and area are four separate checks, all met at once.
Use this diagram

Egress windows on the B1

Egress and stairs sit in public safety and special construction, 17% of the B1. The base limits are the same in the 2021 and 2024 editions, but the sections are not (R310 in 2021, R319 in 2024), so read the section in your own copy before you trust any list. Practice answering which of the four limits a given window fails.

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Public Safety and Special Construction

In a new bedroom, the only emergency escape window has a keyed sash lock, with the key hanging on a hook beside the window. What should the inspector do?

Press A-D or 1-4 to choose an answer while this question is on screen.

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How to check an egress window

  1. Decide if one is required. Each sleeping room needs an emergency escape opening, and so do basements and habitable attics, with the exceptions the section lists. The section is R310 in the 2021 IRC and R319 in the 2024 edition.
  2. Open the window as it normally operates and measure the clear opening. Do not measure the frame or the glass.
  3. Check four limits. The usual base values are a clear area of at least 5.7 square feet, or 5 square feet for a grade-floor opening, a clear height of at least 24 inches, a clear width of at least 20 inches and a sill no more than 44 inches above the floor.
  4. Do the area math. Convert 5.7 square feet to square inches, which is 820.8. A clear height of 24 inches needs a clear width of at least 34.2 inches to reach that area, because 24 x 34.2 = 820.8. So a window can meet both the height and the width minimums and still fail on area.
  5. Check the operation. The opening must work from the inside in an emergency. Read the operation rules, and the rules for any bars, grilles or covers over the opening, in your edition.
  6. Check the window well. When the sill is below grade, the opening needs a well of a minimum size, and a deep well needs a permanent ladder or steps. The egress opening check works through the numbers.

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Common mix-ups

  • Net clear opening versus rough opening. The limits apply to what is left after the sash and frame take their share. See net clear opening versus rough opening.
  • Egress window versus egress door. A door can serve as the escape opening where it meets the same rules. The window rules are one way to comply, not the only one.
  • Egress versus light and ventilation. A window that gives light and air to a room is a separate requirement. One window can serve both only if it meets each set of limits.
  • Sill height is to the bottom of the clear opening. It is not to the bottom of the frame or the glass.

Practice it

Run a few windows through the egress opening check and compare its answers with your own math. Then read net clear opening versus rough opening and guard versus handrail, which belong to the same area of the book, or browse the IRC terms glossary.

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