The International Residential Code sets common rules for handrails, guards and baluster openings. Most U.S. jurisdictions adopt some version of it, but with local changes, so treat this as orientation and verify before you build.
The International Residential Code, or IRC, is a model code published by the International Code Council. It does nothing on its own until a state, county or city adopts it, and each jurisdiction chooses an edition and often adds amendments. The numbers below are drawn from commonly cited model-code provisions for one- and two-family homes, and your local building department has the final word.
Rules also differ for commercial buildings, for multifamily housing and for accessibility. If a permit is required for your project, ask the building department which edition applies, whether a drawing is needed and when inspections occur. Do this before you buy parts, because a rail that is a half inch out of range can mean starting over.
The two are different parts with different jobs. A handrail is what you grip while climbing or descending. A guard is the barrier along an open side that stops a person from falling off the edge. A single assembly can serve both purposes, but the code treats them separately, and each has its own height and opening rules.
Under the model code, a handrail is required on at least one side of a flight of stairs with four or more risers. A guard is required along open sides of walking surfaces, including stairs and landings, that are more than 30 inches above the grade or floor below within a short horizontal distance of the edge.
The model code calls for the top of the handrail to be between 34 and 38 inches above the line connecting the tread nosings. That range allows some design flexibility, but a rail outside it will fail inspection. The handrail should run continuously along the flight, and its ends should return to the wall or terminate at a newel post or safety terminal so that clothing does not snag.
Grip size matters, because a rail you cannot wrap your hand around is not doing its job. For a circular profile, the model code calls for a diameter of 1-1/4 to 2 inches. Non-circular profiles are allowed if the perimeter is at least 4 inches and, for perimeters up to 6-1/4 inches, the largest cross-section is no more than 2-1/4 inches. Larger profiles need graspable finger recesses. Where a rail runs along a wall, leave at least 1-1/2 inches of clearance between the rail and the wall so a hand can fit.
On flat surfaces such as a landing or open floor edge, the model code asks for guards at least 36 inches high. On the open side of a stair, the guard is measured from the nosing line and the minimum can be lower, so many stairs use a rail between 34 and 38 inches that serves as handrail and guard together. Check how your jurisdiction handles this.
Baluster spacing is limited by a sphere test. In general, a guard may not have openings that allow a 4-inch sphere to pass. On the open side of stairs, the model code allows openings that stop a 4-3/8 inch sphere, and the triangular gap formed by the tread, riser and bottom rail of the guard must not pass a 6-inch sphere. Open risers on stairs are also limited so that a 4-inch sphere cannot pass through.
| Item | Model-code value (verify locally) |
|---|---|
| Handrail height | 34 to 38 inches above nosing line |
| Circular grip size | 1-1/4 to 2 inches |
| Wall clearance | At least 1-1/2 inches |
| Guard height on flat surfaces | At least 36 inches |
| Typical guard opening | Must stop a 4-inch sphere |
| Opening on open side of stairs | Must stop a 4-3/8 inch sphere |
| Triangle at tread, riser and rail | Must stop a 6-inch sphere |
The same section of code that governs rails also governs the stair itself. Under the commonly cited model-code limits, the maximum riser height is 7-3/4 inches, the minimum tread depth is 10 inches, the minimum clear width is 36 inches and the minimum headroom is 6 feet 8 inches. Tread depth, riser height and nosing projection should not vary by more than 3/8 inch within a flight. Where treads are less than 11 inches deep, a nosing projection between 3/4 and 1-1/4 inches is called for.
These numbers matter to anyone replacing treads, because a thicker tread can change the riser height at the top or bottom step and trigger a nonuniform stair. Measure before and after, and plan the change with the building department.
The code also requires that guards and handrails resist specified loads, and it does not matter how handsome a rail is if it moves under weight. Newel posts should connect to framing or blocking, not only to finished flooring. Balusters should be fastened at both ends. Wall-mounted handrails need brackets screwed into studs or blocking.
A rail should feel solid when you push on it hard. If a newel flexes or a balustrade rattles, find the cause rather than adding caulk or shims. Our stairs and railings service covers how this work is approached.
Call or visit your local building department and ask four questions. Which code edition is in force? Do I need a permit for this stair or railing work? Are there local amendments to handrail or guard rules? What inspections are required? Take photos and measurements, since they can answer questions faster than a description.
Tread species and appearance are separate choices from code, and are covered in our stair tread guide. For help with the build, send a project inquiry.
The model residential code calls for 34 to 38 inches above the nosing line. Some jurisdictions differ, so confirm with your local building department.
The model code generally requires that a 4-inch sphere cannot pass through guard openings, with a 4-3/8 inch allowance on the open side of stairs. Local rules may differ.
The model code requires a handrail on at least one side of a stair with four or more risers. Some jurisdictions or situations call for more, so check locally.
Only where adopted. States and localities adopt a version of it, often with amendments, so your local building department determines the rules that apply.
Describe the room and the woodwork you have in mind, and we will reply with questions and next steps.