Witches’ stairs are one of the most space-efficient staircase layouts used in small homes, lofts, and converted attics. The steps alternate left and right in a checkered pattern, which lets the stair climb much steeper and run much narrower than a conventional staircase. The design picked up a wave of social media attention after being linked to an old urban legend about the Salem witch trials, but the geometry is real: alternating tread stairs can cut the floor footprint of a staircase by roughly half. Whether you are building stairs for a tight floor plan or simply comparing layouts, the sections below explain how the design works, where it fits, and where building codes draw the line.
What Are Witches’ Stairs?
An alternating tread stair, commonly called a witches’ stair, uses treads that are about half the depth of a standard step. Each tread is offset to one side of the center line, so your left foot lands on one level while your right foot lands on the next level up. The result is a stair that climbs at a much steeper pitch while still giving each foot a reasonably deep surface to stand on.
How the Alternating Tread Pattern Works
Instead of a continuous run of full-width treads, the stair alternates between left-side and right-side steps. One side of each tread is cut back, leaving an open notch on the opposite side of the stair. That staggered geometry is what makes the steep angle possible. A conventional stair pitches at roughly 30 to 37 degrees, while an alternating tread stair commonly runs between 60 and 70 degrees. Users report that the pattern feels odd for the first few climbs and becomes natural within a week or two.
The structure is simpler than it looks. Unlike cantilevered stairs, which hang each step from a hidden steel stringer or a wall pocket, most alternating tread stairs sit on two straight stringers with the treads notched into place. That makes them practical for do-it-yourself framing in attics and lofts, and prefabricated steel and wood kits are available when you want an engineered product.
Why the Name Sticks
The name comes from a folk tale that accused witches of being unable to climb the alternating steps. No historical record supports the story, and no colonial home has ever been documented as using the layout for protection. The label survived anyway because it is memorable, and it now appears in product catalogs and building discussions as a synonym for space-saving stairs.
The Myth and the Real History
The legend places witches’ stairs in 17th century Massachusetts during the Salem witch trials. The claim was that homeowners built alternating steps to keep witches from entering upper floors, since a witch supposedly could not climb the staggered treads. Researchers have found no period documentation for the practice, and historians treat the story as folklore rather than architectural fact.
Separating Legend From Fact
The documented history is more practical. Alternate-tread stairs were popularized by Thomas Jefferson, who used them at Monticello to reach upper floor levels in narrow spaces. The layout also appeared aboard ships, where every inch of floor area is valuable, and in libraries and small offices where a full stair run would consume too much room. Tiny houses and micro-apartments have brought the design back into residential use.
To see why the layout works, it helps to name the components. The main parts of stairs include the stringers that carry the load, the treads you step on, the risers that close the vertical gaps, and the handrails that guide you. In an alternating tread stair, the stringers stay the same, but the treads are cut shorter and staggered so the rise per step can increase well beyond the standard 7 inches.
How Much Space Alternating Treads Save
The savings come from two changes: the steeper pitch and the narrower width. A typical residential stair has a rise of about 7 inches, a tread depth of 10 to 11 inches, and a width of 36 inches. An alternating tread stair for the same floor-to-floor height uses a rise of 8 to 9 inches, an effective tread depth of 5 to 6 inches, and a width of 24 to 30 inches. The floor run needed to climb 9 feet drops from about 11 feet to roughly 5 to 6 feet.
| Property | Conventional stair | Alternating tread stair |
|---|---|---|
| Rise per step | About 7 in (18 cm) | 8–9 in (20–23 cm) |
| Tread depth | 10–11 in (25–28 cm) | 5–6 in (13–15 cm) |
| Typical width | 36 in (91 cm) | 24–30 in (61–76 cm) |
| Pitch angle | 30–37 degrees | 60–70 degrees |
| Floor run for a 9 ft rise | About 11 ft (3.4 m) | 5–6 ft (1.5–1.8 m) |
Where They Fit Best
The layout earns its keep in spaces that see occasional use: attic access stairs, mezzanine steps, loft beds, storage platforms, and utility rooms. Homeowners also install them in cabins, tiny houses, and boat interiors where a conventional stair simply does not fit. For frequently used routes, the steep pitch is a compromise that most households will not accept.
Measuring Your Available Run
Before choosing a layout, measure the total vertical rise from finished floor to finished floor. Divide that rise by the 8 to 9 inches you plan for each step to estimate the number of treads. Multiply the number of treads by about 7 inches of horizontal projection per tread to find the floor run you need. If the result fits your space, an alternating tread design is a candidate.
Outdoor versions of steep stairs follow different rules. If you are adding access to a deck or a garden level, building deck stairs to code involves minimum tread depths, maximum rises, and guardrail heights that do not apply to interior attic steps.
Safety Limits and Code Reality
Steep stairs are a fall hazard, and the alternating tread layout is steeper than almost anything else you can build. Falls on stairs send more than a million people to emergency rooms in the United States each year, and the risk climbs with pitch. That is why model building codes treat alternating tread stairs as a special device rather than as ordinary stairs.
The International Building Code lists the layout under the heading of alternating tread devices and allows it only for limited uses, such as access to mezzanines, storage areas, and equipment spaces in certain occupancies. The International Residential Code takes a similar position, permitting the design mainly for attic and limited-access situations rather than as the primary stair between main living floors. Local amendments vary, so the permit desk at your building department is the final authority.
Handrail Requirements
Codes that allow alternating tread devices typically require a handrail on both sides, with a graspable profile and continuous support through the full climb. The open side of each tread leaves no wall to grab, which makes the double handrail essential. Some manufacturers add a center rail or a full guard where the stair rises more than a few feet.
Who Should Avoid Them
Children, older adults, anyone with mobility limitations, and anyone who carries laundry, tools, or groceries should not rely on alternating tread stairs as a daily route. Use them where traffic is light and a fall would be less costly. If an existing staircase has settled, creaks, or pulled away from its framing, fixing rough framed stairs should happen before any redesign work begins.
Types of Steep and Space-Saving Stairs
Architects sort the types of stairs by shape, support method, and tread geometry. The common shapes are straight, L-shaped, U-shaped, and spiral. The space-saving group adds ship’s ladders, alternating tread stairs, and spiral stairs, each with its own trade-off between footprint, comfort, and safety.
Ship’s Ladders vs. Alternating Treads
A ship’s ladder pitches between 50 and 70 degrees and keeps full-width treads, but the treads are narrow and shallow, so climbers use both hands on the rails and often descend facing the ladder. Alternating tread stairs give each foot a deeper surface and a more natural walking motion, which many users find more comfortable, though the open sides still demand attention. Spiral stairs sit between the two: a tighter footprint than a straight stair but wider treads than a ladder, at the cost of a winding path that is awkward with large objects.
Upkeep also differs. Wood alternating treads need the same periodic sealing as any interior stair, while steel ship’s ladders and spiral kits are mostly maintenance-free apart from tightening hardware. Factor the finish work into the budget before you commit to a material.
Building or Retrofitting Your Own
A straight alternating tread stair is a realistic weekend project for someone comfortable with a circular saw and a framing square, but check the local code and pull a permit before cutting lumber. Factory-built alternating tread stair kits are also available and arrive with engineered stringers and pre-cut treads that remove most of the layout risk.
Step-by-Step Layout for a Straight Run
- Measure the total rise from the lower floor to the upper landing.
- Divide the rise by 8 to 9 inches to set the number of steps, then adjust so every step has the same height.
- Lay out the stringers with alternating notches, marking one side of each tread position.
- Cut the treads to half width plus the nosing you want on the open edge.
- Install the stringers, fix the treads with construction adhesive and screws, and add the double handrails.
- Test the climb with both hands on the rails before the stair goes into daily use.
Stringer math and code checks are the same for any stair layout; the full stairs guide on tread and riser calculations applies here with one change, which is that each tread is cut half-width and staggered.
When the space is too tight for wood framing or the route is outdoors, concrete stairs remain the durable alternative for basements and exterior entrances. Whatever material you choose, remember that an alternating tread stair saves floor space, not caution: test it, maintain the handrails, and keep it for the routes that matter least.