Switchback stairs. Stacked flights, intermediate landings, half the floor footprint.

Why switchback

When floor-to-floor exceeds one flight.

OBC §3.4.6 caps a single stair flight at 16 risers — roughly 9 ft of rise — before a landing is required. Above that, switchback is usually the right answer: two flights with a 180-degree turn at the mid-landing, both flights stacked over the same floor footprint. The configuration is the most common one on multi-story interior egress and on most exterior fire-escape retrofits.

When switchback wins over straight-run

• Floor-to-floor > 9 ft — code-required intermediate landing makes a switchback geometrically natural.
• Limited run space — a 12 ft rise needs ~17 ft of horizontal run as a straight-run. The switchback halves it.
• Egress capacity calculation — easier to size two narrower flights than one wide flight in some occupant-load cases.
• Architectural preference — switchbacks integrate well with double-loaded corridors.

Detail decisions

• Mid-landing depth — minimum equal to flight width. We typically detail it 1200 mm × 1200 mm or larger.
• Guard continuity — guard wraps around the landing without dropping below 42" anywhere along the egress path.
• Tread alignment — top of landing aligns with top of last tread; we shop-mock complex transitions before paint.

Typical parameters

• Rise range9 ft – 25 ft (multi-flight)
• Risers per flightup to 16
• Mid-landing≥ flight width × flight width
• Treadgrip-strut / bar-grate / checker-plate
• Guard height42" (OBC §3.3.1.18)
• Live load4.8 kPa + 1.3 kN concentrated
• Finishshop primer / galvanized / powder-coat
• Lead time4 – 6 weeks from sign-off