2021 IRC R310-R312
This lesson covers the life-safety category that inspectors and rehab crews see quoted more than any other set of numbers in the book: how a person gets out of a house, how they cross a stairway without falling, and what keeps them from going over an open edge. IRC Sections R310 through R312 set these requirements, and because they govern how someone escapes a fire or survives a fall, they get enforced strictly.
Every dwelling unit needs at least one side-hinged egress door, with a clear width of not less than 32 inches (measured between the face of the door and the stop, with the door open 90 degrees) and a clear height of 78 inches (top of threshold to bottom of stop) (R311.2). The path to it must not require travel through a garage, and it must open to a public way or to a yard or court that opens to one (R311.1). Other exterior doors on the house are not held to this size, which is why a sliding patio door is common as a second, non-required exit. Hallways that form part of the path to that door must be at least 36 inches wide (R311.6).
Exterior landings at doors matter as much as the door size. A landing must be at least as wide as the door it serves and not less than 36 inches deep in the direction of travel (R311.3). At the required egress door, the landing may be no more than 1-1/2 inches below the top of the threshold. An exception allows the exterior landing to drop as much as 7-3/4 inches, one riser, but only where the door does not swing over that landing; an outswinging door is not allowed to sweep someone off a step that low.
Every sleeping room needs its own emergency escape and rescue opening (EERO), and so does every basement and every habitable attic, whether or not the basement contains a bedroom (R310.1). Sleeping rooms in basements of sprinklered dwellings have their own exception (R310.1, Exception 2). A narrow exception also excuses a basement used only to house mechanical equipment, and not exceeding 200 square feet, from needing one. Add storage, finish the space, or push it past 200 square feet and the exception is gone. This is the single most common life-safety item that a basement rehab or finish-out project in Gulf Coast housing stock triggers: an older home finished below grade decades ago, with no escape window, cannot legally be called a sleeping space until one is added.
The 24-inch height and 20-inch width figures are floors, not a formula that automatically produces a compliant window. A 24 by 20 inch opening is only 3.3 square feet, well short of the 5.7 (or 5.0) square feet required, so a compliant window has to clear one or both minimum dimensions by a wide margin to reach the required area. Checking an EERO means checking the height, the width, and the area separately; passing two of the three checks does not satisfy the code.
Security bars, grilles, and window well covers are permitted over an EERO, (R310.4.4), but only where they are releasable or removable from the inside without a key, tool, or force greater than normal operation of the opening, and the opening still meets the required net clear size. This is one of the most consequential checks in rehab work: a homeowner who bolted bars over a bedroom window for security has very often created an unreleasable barrier that fails the room for sleeping use, no matter how good the window behind the bars is.
R311.7 sets the geometry that keeps a stairway from becoming a trip hazard. Maximum riser height is 7-3/4 inches; minimum tread depth is 10 inches; and within a single flight, no riser or tread may vary from the smallest one in that flight by more than 3/8 inch. Minimum clear width is 36 inches, measured above the handrail height; a handrail is allowed to project up to 4-1/2 inches into that width, so a 36-inch stairway with one handrail still needs to leave 31-1/2 inches clear (27 inches clear with handrails on both sides). Minimum headroom is 6 feet 8 inches, measured vertically from the sloped line connecting the tread nosings, maintained over the full run including landings.
Nosing projections between 3/4 inch and 1-1/4 inches are required where the tread depth is less than 11 inches (R311.7.5.3); once treads reach 11 inches there is enough foot room without an overhang. On winder treads, the 10-inch minimum depth is measured at the walkline, located 12 inches from the inside of the turn (R311.7.4), which reflects where a foot actually lands going around the turn, with a separate 6-inch minimum at any point. Spiral stairways get relaxed geometry in exchange for their compact footprint: 26 inches minimum clear width, 9-1/2 inches maximum rise, and 6 feet 6 inches minimum headroom.
Landings are required at the top and bottom of each flight, at least as wide as the stairway served and not less than 36 inches deep in the direction of travel (with an exception at the top of an interior flight where the door does not swing over the stairs). The maximum vertical rise between landings is 12 feet 7 inches (151 inches); a longer flight needs an intermediate landing, because an uninterrupted fall down that much stair is far more likely to be serious.
A handrail is required on at least one side of any flight with four or more risers (R311.7.8). The top of the rail must be 34 to 38 inches above the tread nosings. A circular handrail qualifies as a graspable Type I profile at an outside diameter of not less than 1-1/4 inches and not more than 2 inches; a non-circular profile has its own perimeter dimensions, but the same idea applies either way: an oversized decorative cap or a flat 2x4 rail cannot actually be gripped to arrest a fall. The rail must be continuous for the full length of the flight, with ends that return toward a wall or guard, or terminate at a post, rather than stopping in open air where a sleeve or bag can catch. Clearance between the rail and an adjacent wall must be at least 1-1/2 inches, enough for a hand to wrap the rail without scraping.
The 36-inch horizontal measurement matters on sloped sites: a deck or porch only 24 inches above grade right at the house wall can be well over 30 inches above grade a few feet out, and the guard requirement follows the worst condition found within that 36-inch zone, not the condition at the house. The 4-inch sphere rule is a child-safety dimension, sized so a young child's head and torso cannot pass through; the larger 4-3/8-inch and 6-inch allowances apply only at the specific stair locations named above, never to a level porch or deck guard.
In the field
A GCHS inspector walking a rehab project with an unpermitted deck addition should check the same handful of items every time, because they are the ones that cause real injuries and the ones that finish work will hide: riser and tread uniformity, headroom, stair and landing width, handrail presence and graspability, and guard height and opening size at any edge over 30 inches. A deck built with a nailed, unflashed ledger and a guard with 6-inch picket gaps can look finished and still be one of the more dangerous structures on the property; those two defects, ledger attachment and guard openings, come up again and again in older additions built without a permit.
A rehab crew is finishing a basement bedroom. The stair down has 8 risers measuring 7-5/8 inches each and treads of 10-1/4 inches, a 36-inch clear width with one handrail mounted at 36 inches above the nosings, and 6 feet 9 inches of headroom. The proposed egress window has a net clear opening 30 inches wide by 26 inches high. Check both: riser height, 7-5/8 inches, is under the 7-3/4-inch maximum, with no variation between risers, so the stair passes on rise; tread depth, 10-1/4 inches, clears the 10-inch minimum; width at 36 inches with one handrail leaves the code-required 31-1/2 inches clear; headroom at 6 feet 9 inches clears 6 feet 8 inches; and the handrail height of 36 inches falls inside the 34-to-38-inch range. The stair is compliant. For the window: net clear area is roughly 30 times 26 divided by 144, about 5.4 square feet. That clears the 5.0-square-foot allowance for a grade-floor opening (a basement opening with its sill within 44 inches of the adjacent ground counts), and both the 24-inch height and 20-inch width minimums are cleared as well. The window passes on all three checks at once (assuming a sill no more than 44 inches above the floor), which is what makes it compliant, not just close on one number.
1. What size clear opening must the required egress door provide, and what other constraint applies to it?
2. A basement is used only to house a furnace and water heater and measures 180 square feet. Does it need an emergency escape and rescue opening?
3. What is the minimum net clear opening area for an emergency escape and rescue opening on an upper story (not a grade-floor opening)?
4. An inspector measures a proposed egress window at 20 inches wide by 24 inches high. Why does this fail even though it appears to meet both minimum dimensions?
5. What is the maximum sill height permitted for an emergency escape and rescue opening?
6. Security bars are installed over a required bedroom egress window. Under what condition are they acceptable?
7. What are the maximum riser height and minimum tread depth for a residential stairway?
8. An inspector measures risers of 7-1/2, 7-5/8, and 7-15/16 inches within one flight. What is the finding?
9. Minimum stairway headroom is 6 feet 8 inches, measured how?
10. A flight has four or more risers. What does R311.7.8 require?
11. A stairway is 36 inches wide with a handrail on one side. What minimum clear width must remain at and below handrail height?
12. At what height above grade or floor does an open-sided walking surface require a guard, and how is that height measured?
13. A guard has openings on the open side of a stairway. What is the largest sphere the opening may allow to pass, and how does this differ from a level porch guard?
14. An inspector arrives at an unpermitted deck. Riser and tread geometry on the stairs is correct, but the guard has 6-inch gaps between pickets on a walking surface 42 inches above grade. What is the finding?