Guides
Egress Window Requirements (IRC R310) and Tilt-Turn Windows
An egress window is an operable emergency escape and rescue opening that, in the 2021 International Residential Code (IRC) section R310, has a net clear opening of at least 5.7 square feet (0.53 m2), at least 24 inches (610 mm) of clear height, at least 20 inches (508 mm) of clear width, and a sill no higher than 44 inches (1,118 mm) above the floor. A tilt-turn window can meet the rule in turn mode, provided the size, the sill height and the operation all comply.
The figures below were checked against the 2021 IRC as published in a county building-department summary that cites R310 by section. Later editions exist, and adoption varies by state, county and city, so the edition in force on your project governs. Confirm with the local building official.
Which rooms need an egress opening?
Under 2021 IRC R310, basements and every sleeping room need at least one operable emergency escape and rescue opening. The opening must operate from inside the room without keys, tools or special knowledge (R310.1.1). Emergency escape doors qualify as well if they are side-hinged or sliding.
What are the size and height requirements?
| Requirement | Value (2021 IRC) | Section |
|---|---|---|
| Net clear opening area | 5.7 sq ft (0.53 m2) | R310.2.1 |
| Net clear opening area, grade-floor openings | 5.0 sq ft (0.46 m2) | R310.2.1 |
| Net clear opening height | 24 in (610 mm) minimum | R310.2.2 |
| Net clear opening width | 20 in (508 mm) minimum | R310.2.2 |
| Sill height (bottom of the clear opening above the floor) | 44 in (1,118 mm) maximum | R310.2.3 |
| Opening under a deck, porch or cantilever | fully openable, 36 in by 36 in (914 mm by 914 mm) path to a yard or court | R310.2.4 |
Why do the minimum height and width not add up to the minimum area?
A 24 inch by 20 inch opening measures 480 square inches, or about 3.3 square feet, which is less than 5.7 square feet (820.8 square inches). The area is the governing number, and the minimum height and width are floors for each dimension. For a clear height of 24 inches the clear width must be at least 34.2 inches. For a clear width of 20 inches the clear height must be at least 41.04 inches. These pairs follow from the area rule by arithmetic and are not separate code values.
How is the net clear opening measured?
Net clear opening dimensions come from the window's normal operation, and the 44 inch limit is measured to the bottom of the clear opening. A window's rough opening or frame size is therefore always larger than its net clear opening. Check the manufacturer's published net clear opening for the exact size.
What do window wells require?
When the bottom of the clear opening is below adjacent grade, the 2021 IRC requires an area well (R310.4).
- Size: at least 9 square feet (0.84 m2) of horizontal area, with a projection and width of at least 36 inches (914 mm). The well must let the opening fully open. A ladder or steps may project up to 6 inches (152 mm) into those dimensions.
- Ladder or steps: required if the well is deeper than 44 inches (1,118 mm). They must be permanently attached and usable with the window fully open. A ladder needs an inside width of at least 12 inches (305 mm), must project at least 3 inches (76 mm) from the wall, and may have rungs no more than 18 inches (457 mm) apart for the full height. Steps need an inside width of at least 12 inches, treads at least 5 inches (127 mm) deep, and risers no more than 18 inches high.
- Drainage: the well connects to the foundation drainage under R405.1, unless the foundation sits on well-drained soil listed in the code.
- Bars, grilles and covers: these must leave the opening at the required net clear size and must release from inside without a key or tool and without more force than operating the window requires.
Which window types qualify?
The code does not name window types. It sets openable size and operation, so the question is how much of the frame opens at normal operation.
| Type | How it fits |
|---|---|
| Casement (outswing) | The sash swings clear of the opening, so the net opening can approach the frame size, less the hardware and sash edge. |
| Tilt-turn (turn mode) | The sash swings into the room on its side hinges. See the next section. |
| Double-hung and single-hung | Only one sash moves, so the net clear height is about half of the frame's glazed height. |
| Horizontal slider | Only one sash moves, so the net clear width is about half of the frame's glazed width. |
| Fixed | Does not open and does not qualify. |
These are geometry notes, not code listings. The opening that governs is the measured net clear opening of the specific product.
How do tilt-turn windows fit egress rules?
A tilt-turn window has two modes on one handle. In tilt mode the top of the sash pivots inward for ventilation, giving only a narrow gap. In turn mode the sash swings into the room like a door and gives full access. Only turn mode can supply an egress opening. See tilt and turn windows for the mechanism and inward-opening windows for the clearance an inswing sash needs in the room.
Four points decide whether a tilt-turn unit passes:
- Net clear opening in turn mode. The sash stays attached at the hinge side, so the hinge, the folded sash edge and any fixed mullion reduce the clear width. Size the unit from the manufacturer's net clear opening, not from the frame.
- Operation without special knowledge. R310.1.1 allows no keys, tools or special knowledge. Tilt-turn windows use one handle with several positions, and some handles add a button as a second opening step. Inspectors decide whether that operation meets the rule, so show the operating sequence on the submittal.
- Sash position. The open inswing sash sits in the room. Furniture, curtains and a bed near the window can block the sash swing, which is a design issue for the bedroom layout.
- Opening limiters. A device that limits how far a sash opens can prevent egress. Window opening control devices that meet ASTM F2090 are permitted by the 2021 IRC if they are no higher than 70 inches (1,778 mm) above the finished floor. A Green Building Advisor thread describes an inspector rejecting a tilt-turn replacement handle with a second button because it was not certified to ASTM F2090, and notes that aftermarket fall-prevention devices were not readily available for tilt-turn windows. Any device that limits how far a window opens can keep a bedroom window from meeting egress rules.
What about fall protection and local amendments?
Upper-floor windows face separate fall-prevention rules, which the thread above associates with section R312.2.1 and a Minnesota version of it requiring a higher sill. That is a local amendment example. The IRC is a model code, and states and cities adopt and amend it, so sill heights, replacement rules and well details can differ. Boulder County, for instance, adds that cutting a foundation wall for an egress window needs an engineer's design and that non-conforming windows found at inspection must be replaced. Ask the local building department which edition and amendments apply before ordering. For how European products meet local code in general, see do European windows meet US code.
How should you specify egress windows?
- Mark each required egress window on the schedule, by room.
- Record the manufacturer's net clear opening width, height and area in operating position for the exact unit size, and compare against 5.7 square feet (5.0 at grade), 24 inches and 20 inches.
- Record the sill height to the bottom of the clear opening, 44 inches maximum.
- For below-grade openings, show the area well with its 9 square foot, 36 inch dimensions, the ladder if over 44 inches deep, and drainage.
- For tilt-turn units, state turn-mode operation and flag any opening limiter or lock so the inspector can review it at the submittal stage.
Terms used here are defined in the window and door glossary.
Frequently asked questions
Can a tilt-turn window be an egress window?
Yes, if the net clear opening in turn mode meets the size rules, the sill is within 44 inches, and the window opens from inside without keys, tools or special knowledge. The inspector decides whether the handle operation and any opening limiter meet that test.
Do the 24 inch and 20 inch minimums guarantee compliance?
No. A 24 by 20 inch opening is only about 3.3 square feet, so the 5.7 square foot area requirement controls. The opening must be larger than the minimum dimensions.
Does a fixed window count as egress?
No. The code requires an operable emergency escape and rescue opening, so a fixed unit does not qualify.
Does the egress rule apply to window replacement?
Jurisdictions differ. Boulder County, for example, applies the requirement to new construction, remodels and window replacements, so ask the local building department before replacing a window in a bedroom or basement.
Sources
- Boulder County - B10 Emergency Escape and Rescue Openings (2021 IRC R310)
- Boulder County - B30 Safety Glazing (2021 IRC R308)
- Green Building Advisor - Fall protection on European tilt-n-turn windows (passing code)
- Window Hardware Direct - The complete guide to tilt and turn window hardware
- Andersen - Window and door glossary (egress window, WOCD, clear opening area)
Kai Adamek writes SeeWindow. He has spent years in the construction industry and specializes in windows and doors. A frequent traveler, he has visited the United States many times and writes about how European products are specified, rated and ordered for American homes.