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Winder stairs, angled, or curved stair specifications: this document defines winder stairs refers to building code specifications, construction specs, and inspection details for winder, curved or angular stairs: stairs that make a turn without a landing. We include sketches, photographs, and examples of defects used in inspecting indoor or outdoor stairs, railings, landings, treads. The angled stairs shown at page top are not "winders" but also involve irregularly-shaped stair treads. That photo shows angled stair treads squeezing a stairway onto a New York City sidewalk.
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Definition & Properties of Winder Stair Hazards
"Winder" or "curved" stairs refer to stairways that make a turn without including an intermediate landing or platform to provide a flat rectangular turning space. Angled or curved or winder stair treads are a particular trip hazard, especially because of the lack of uniformity and because the tread width at the inside of the angle curve can be too small for safe walking.
Definition of Winder Stairs
Any stairway whose treads do not have parallel edges - IRC R-202 - [14a]
By this definition a circular or spiral stair or curved stair is a winder stairway. What's different, then between a circular stair and a more generic winder stair? Check the photos and descriptions of circular stairs and spiral stairs just above.
Winding or spiral stairways must have a handrail to prevent use of areas where the tread width is less than 6 inches (15 cm).
CA/OSHA Title 8 Section 1626 [paragraph (1) provides:
Watch out: we have on occasion seen placement of handrailings close to the origin of turning axis of winder stairs, such as shown by the red arrows in our photograph at left.
The stair installation shown above has no graspable handrailing along the left side of the upper portion of the stairway. So the very handrail intended to prevent use of the too-small tread area actually does not form a barrier along those treads (it is installed on the last rectangular tread above the triangular steps) and worse, because of the lack of anything else to grasp, the walker actually has to hold on to a guard or rail that directs him or her to step precisely where we don't want - on the tiniest part of the tread.
The building owners added the vertical grab-bar and short "handrailing" shown (orange arrow) in our photo. Indeed this gives the stairway user something to grasp on-to.
Unfortunately it also directs the descending or ascending stair user to walk along the inside (red arrow) of several triangular stair treads.
By mounting the graspable handrail close to the innermost point or origin of the winder stair (or circular or spiral stair) turn, you encourage or even force stairway users to walk on the smallest (and most hazardous) portions of the stair treads.
Stairway winders As the sketch, courtesy Carson Dunlop, shows, only one set of winders should be allowed in a staircase, and the dimensions shown address tripping hazards.
This sketch shows the minimum tread width and radius for curving stair treads such as the stairs in our photograph above.
[Click to enlarge any image]
In our sketch below you can see that a 90 degree turn is effected by three sequential triangular stair treads. Walking near the inside corner of this turn is difficult because of the irregular and small step area. At right are stairs that make a 90 degree turn accomplished over the rise of the entire stairway. In either case, there is no intermediate landing.
In sum, stairway winders or turns involve triangular treads to complete the turn as you can see in our photo at right (note the handrail which is not grasp-able and not child safe).
As the sketch above left shows, courtesy Carson Dunlop, in a staircase that actually makes a 90 deg. turn (as opposed to the curved stair at right) only one set of winders should be allowed in a staircase, and the dimensions shown address tripping hazards.
Of course more turns may be involved in a stairway than a simple angled or curved stair, such as the case of a circular stair, or a large, wide circular stairway that rises over a distance requiring an intermediate landing.
Our photos below illustrate several very steep winding stairways, first in the Mansfield Hotel in Manhattan, then in a less often used location, steep attic stairways in private homes.
At left our photo illustrates a beautiful stairway in the Mansfield Hotel on West 44th St., in Manhattan. This Beaux Arts style hotel, built in 1903, was designed by James Renwick and according to the hotel's own history page the structure was originally
Most guests use the hotel's elevators, but we tried the stairs down from a seventh floor room. The stair treads near the stair top are a bit risky, as the narrow inside corner of the winding stair treads is too small for most feet, while the handrailing, with an excellent graspable profile, is by force located on the inside of the turn, inviting stair users to walk closest to the most narrow tread portions. I asked a guest couple how they liked the stairway as we descended together to the lobby. "Beautiful, said one, but I would not like to have to run down these stairs in the event of a fire." - 
At below left we see more serious stair trip and fall hazards: storing items on the stairs is of course another trip/fall hazard made worse in a narrow stairway where there is no room to bypass the items that should not be there in the first place. Meanwhile at below right you will note that the vertical stair ascent is so steep as to nearly comprise a ladder - a difficult stair to negotiate, exacerbated by the absence of any grab rail.
Our stair photo at shows tricky angled stairs that were squeezed onto a sidewalk in New York City. A passerby agreed to model the risk of falling.
In our OPINION the crypto-trip hazard at angled stairs such as these is the fact that the stair treads and noses are not parallel to the direction of travel. This hazard is similar to circular or winder stair hazards but without the too-small tread walking area.
But walking down these stairs in the direction guided by the handrail requires the user to step on stair tread noses that are on an angle to the direction of travel, inviting a twisted foot or ankle or possibly a fall.
For a complete list of articles on stairs, railings, and ramps, their inspection, trip hazards, and good design, see STAIRS, RAILINGS, LANDINGS, RAMPS - INSPECTIONS, CODES.
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