What exactly is a switchback stair?

A switchback stair has two straight flights running parallel in opposite directions, connected by a flat landing where you turn 180 degrees. It is the most compact way to connect two floors when a single straight flight will not fit, and it is standard in apartments, townhouses, and basement stairwells.

How deep does the landing need to be?

At minimum, the landing must be at least as deep as the stair is wide, so a 36-inch-wide stair needs a 36-inch-deep landing. In practice, going a few inches deeper makes the 180-degree turn noticeably more comfortable, especially on stairs that get daily use.

How do I split the risers between the two flights?

Divide the total rise by your target riser height to get the total riser count, then split it as evenly as possible between the two flights. Both flights should end up with the same riser height, because the 3/8-inch uniformity rule applies across the entire stairway, not within each flight.

What is the minimum width for switchback stairs?

Residential switchback stairs must be at least 36 inches wide under the IRC, and the landing must be at least as wide as the stair. Many builders go 40 to 42 inches wide on switchbacks because the turn feels much less cramped with the extra inches.

How do I check headroom under the upper flight?

Measure vertically from the nosing line of the lower flight or landing up to the underside of the upper flight. You need at least 6 feet 8 inches of clear space at every point. In tight stairwells this is the dimension most likely to fail, so verify it before framing.

Do handrails have to continue around the landing?

Yes. Handrails must run continuously along both flights and around the landing so you never have to let go mid-turn. Any open side of the landing also needs a guard at least 36 inches high, with balusters spaced so a 4-inch sphere cannot pass through.

Can a door open onto the switchback landing?

It can, but the door swing must not reduce the landing below its required depth when the door is open. Codes limit how far a door may project over a landing. If a door must open there, make the landing deeper than the minimum to absorb the swing.

Switchback Calculator

What Is the Switchback Calculator?

Switchback stairs solve one of the hardest layout problems in home building: getting from one floor to the next in a tight footprint. Instead of one long straight flight, a switchback stair splits the climb into two parallel flights that run in opposite directions, joined by a flat landing where you make a 180-degree turn. You see them in apartments, townhouses, split-level homes, and basement stairwells, anywhere the total run of a straight stair simply will not fit. This free switchback stair calculator works out the full geometry for you: how many risers go in each flight, the exact riser height and tread depth, the landing depth needed for a comfortable turn, the total run and footprint, and the headroom where the upper flight passes over the lower one. Because both flights share one continuous walking path, small errors compound fast. A landing that is two inches too shallow, or risers that differ between the two flights, will fail inspection and feel wrong underfoot every single day. Getting the numbers right before you frame is exactly what this calculator is for.

How to Use This Calculator

Measure the total rise from the finished lower floor to the finished upper floor, including all flooring. Every riser in both flights is calculated from this one number, so measure it twice.
Split the total rise into two flights. For the most comfortable result, give each flight the same number of risers so the riser height ends up identical on both flights.
Pick a target riser height between 7 and 7-1/2 inches. The IRC allows up to 7-3/4 inches, but a slightly lower riser is easier to climb and keeps both flights consistent.
Enter your tread depth. The IRC minimum is 10 inches, and keeping the same depth on both flights and across the landing keeps your stride steady through the turn.
Set the stair width. Residential stairs must be at least 36 inches wide, and the landing must be at least as wide as the stair it serves.
Set the landing depth and the gap between the parallel flights. The landing needs enough depth for a full 180-degree turn, and the gap needs room for handrails and guards on the inner edges.

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