# Egress Window Requirements: The R310 Numbers That Count Canonical URL: https://www.simplywise.com/blog/egress-window-requirements/ Plain text: https://www.simplywise.com/blog/egress-window-requirements/llms.txt Publisher: SimplyWise, Inc. (https://www.simplywise.com) Published: September 21, 2026 Updated: October 4, 2026 Category: How to Estimate Summary: Egress window requirements under IRC R310: net clear opening, sill height, window well size, which rooms need one, and a real window measured against it. --- ## Egress Window Requirements: The R310 Numbers That Count Every figure quoted to the subsection that publishes it, cross checked against a second jurisdiction, measured against a real window. At a glance 1. 2021 IRC: 5.7 square feet of net clear opening. Clear height 24 inches, clear width 20. Opening bottom within 44 inches of the floor. 2. Net clear opening is the hole with the sash operated. Not the rough opening, not the glass. 3. Basements, habitable attics and sleeping rooms need one. A mechanical-only basement under 200 square feet does not. ## What are the egress window requirements? Under Section R310 of the 2021 International Residential Code, an emergency escape and rescue opening needs a net clear opening of 5.7 square feet. It needs 24 inches of net clear height and 20 inches of net clear width. The bottom of that opening sits no more than 44 inches above the finished floor. Grade floor openings get 5 square feet instead. ## Which rooms the egress window requirements cover Settle this before you quote. R310.1 requires one operable opening in basements, in habitable attics, and in every sleeping room. Where a basement holds sleeping rooms, each one needs its own. Exception 1 is the one that pays. A basement used only to house mechanical equipment, under 200 square feet total, is exempt. So are storm shelters. ### What a basement remodel triggers R310.7 draws the line cleanly. A new sleeping room created in an existing basement gets an opening under R310.1. Every other alteration or repair does not. Frame a bedroom and you own a window well. Refinish it as open rec room and you do not. ## Egress window requirements, subsection by subsection ### The opening itself R310.2.1 sets minimum size at 5.7 square feet of net clear opening. An exception drops grade floor openings to 5. A grade floor opening is one whose clear opening sits within 44 inches of the finished ground beside it. R310.2.2 sets the dimensions: 24 inches of net clear height, 20 of net clear width, obtained by normal operation. R310.2.3 caps the opening bottom at 44 inches above the floor. ### The window well R310.4 applies whenever the opening bottom sits below adjacent grade. R310.4.1 wants at least 9 square feet of horizontal area. The projection and the width are at least 36 inches, sized so the window opens fully. R310.4.2 requires a permanently affixed ladder or steps once the well is deeper than 44 inches. That is well depth, not depth below grade. R310.4.2.1 gives the ladder 12 inches of inside width and rungs 18 inches on center. ### The subsection numbers moved Under the 2018 IRC these figures live at different addresses. R310.2.1 carried area and both dimensions. R310.2.2 was sill height, R310.2.3 window wells. Cite 2021 numbering to a 2018 jurisdiction and your reviewer will red line it. Amendments are real. Fargo, North Dakota prints the model text, then its own changes underneath. One allows a 48 inch sill below grade. Read the adopting ordinance. ## A real window measured against R310 Net clear opening is the free area with the sash fully operated. Andersen prints it beside overall window area in the 400 Series tilt wash specification. | Unit | Overall window area | Clear opening | R310.2.1 verdict | | --- | --- | --- | --- | | TW2846 | 13.28 sq ft | 5.05 sq ft, 29 7/8 in by 24 1/4 in | Grade floor only | | TW2852 | 15.14 sq ft | 5.77 sq ft, 29 7/8 in by 27 3/4 in | Passes anywhere | | TW3046 | 14.85 sq ft | 5.72 sq ft, 33 7/8 in by 24 1/4 in | Passes anywhere | Run the arithmetic. The 5.7 square foot minimum is 820.8 square inches. The grade floor minimum is 720. The TW2846 gives 5.05 square feet, or 727 square inches. It clears the grade floor bar and misses the general one. That is 13.28 square feet of window producing 5.05 of hole. Second floor bedroom, it fails. Basement well within 44 inches of grade, it passes. Same catalogue number. ## Quote the opening before you cut it SimplyWise Cost Estimator turns a photo into an itemized estimate in about 6 seconds, with material and labor lines. Pricing is $29.99/mo or $239.99/yr, about $20/mo on annual, with a 7-day free trial. ## Where egress window requirements show up on a job ### What the inspector measures The inspector opens the sash and measures the hole. Then finished floor to its bottom. Then the well. A tape off the rough opening proves nothing. ### What it costs you to get wrong Wrong unit means saw cutting the wall twice, a new header, a re-dug well, a re-inspection. That rework lands on you. Our basement waterproofing cost (https://www.simplywise.com/blog/basement-waterproofing-cost/) guide covers drainage. ## Common mistakes with egress window requirements ### Measuring the wrong thing Quoting off the rough opening or the glass. Both overstate it badly. ### Assuming a big window passes A tall double hung looks generous and still misses 5.7 square feet. Only the lower sash travels. Casements pass more easily. ### Sizing the well to the window Nine square feet, 36 inches of projection, a ladder past 44 inches. A well sized to the window fails on its own. 1. Confirm the room is in scope Basement, habitable attic or sleeping room, R310.1. 2. Read the published clear opening From the spec sheet, never the catalogue size. 3. Measure the sill and the grade Within 44 inches of the floor. Grade floor or not? 4. Size the well and the ladder Nine square feet, 36 inch projection, ladder past 44 inches. ## Keep reading - Construction Calculators Hub (https://www.simplywise.com/blog/construction-calculators/) - Basement Waterproofing Cost (https://www.simplywise.com/blog/basement-waterproofing-cost/) - Drywall Installation Cost (https://www.simplywise.com/blog/drywall-installation-cost/) - SimplyWise Pricing (https://www.simplywise.com/blog/pricing/) ## Sources ### Code text, 2021 IRC - Routt County CO, Section R310 code and commentary (https://www.co.routt.co.us/DocumentCenter/View/15206) (2026-09-14). - Spearfish SD, egress window handout, 2021 IRC (https://www.spearfish.gov/DocumentCenter/View/5232/Egress-Window-Handout-PDF) (2026-09-14). ### Code text, 2018 IRC numbering - Fargo ND, egress windows handout and local amendments (2026-09-14). - Jersey County IL, escape and rescue handout (https://jerseycounty-il.gov/wp-content/uploads/2022/10/Emergency_Escape___Rescue_Openings_pg_1.pdf) (2026-09-14). ### Manufacturer specification - Andersen 400 Series tilt wash opening and area specifications (https://www.andersenwindows.com/-/media/aw/files/technical-docs/area-and-opening-specifications/area-openingspecifications-windows--400series-tilt-washhungfull-frame.pdf) (2026-09-14). ### Product - SimplyWise Cost Estimator (https://apps.apple.com/us/app/simplywise-cost-estimator/id6670619664) (2026-09-09). ## Common questions about egress window requirements ### Size and sill **What size does an egress window have to be?** R310.2.1 of the 2021 IRC sets 5.7 square feet of net clear opening. A grade floor opening drops to 5. R310.2.2 adds 24 inches of clear height, 20 of width. **How high can an egress window sill be?** R310.2.3 caps the clear opening bottom at 44 inches above the finished floor. Measure the opening, not the rough sill. Below grade, add a window well. **Is net clear opening the same as the rough opening?** No, and that is the expensive mistake. Andersen lists one tilt wash unit at 13.28 square feet of window, 5.05 of clear opening. ### Rooms and wells **Does an unfinished basement need an egress window?** Yes, under R310.1. Exception 1 covers storm shelters and a basement housing only mechanical equipment under 200 square feet. **How big does an egress window well have to be?** R310.4.1 requires at least 9 square feet of horizontal area. The projection and width are at least 36 inches. Past 44 inches deep, add a ladder. --- ## About SimplyWise SimplyWise, Inc. (New York, NY) builds mobile apps for contractors, tradespeople, and small business owners. 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