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Building stair tread nose projection: codes & specification requirements for stair design. This article discusses how stair tread nose projection should be designed, shaped & sized. Should stair tread nose projections be eliminated? What about open riser stairs? Stair tread nose research & stair code citations are included.
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[Click to enlarge any image]
The leading edge of treads of stairs and of landings at the top of stairway flights. - IBC 1002 [14a]
At left we illustrate stairs constructed with no tread nose projection - a common design in areas where stairs are often built of tile and masonry.
These steps to include a nice color indication of the location of stair risers - but visible mostly to people ascending the steps.
The steps in the photo above were observed in Barcelona, Spain and if wet were incredibly slippery. No handrailinbgs were present. The dark green edge tile on the first stair tread may tell a story of a stair step edge breakaway failure.
Research on stair tread nose specification history points out that designs for stair treads that project out over the tread below probably originated in the construction of tall steep stairs with too-narrow treads in the first place.
But research also concludes that while there are certainly trip hazards associated with projecting stair tread nosings, when designed within proper limits the stair tread nose probably improves stair safety.
Watch out: Our photo at left shows a tall steep stair design that is unsafe at any speed, ascending, descending, with open risers, narrow treads, over-cut stair stringers, wet algae-covered slippery treads, no landing, no handrailings, open guardrails on the deck above.
When you encounter a stair such as this one it is reasonable to presume that the builder probably made multiple construction and safety errors, leading to a suggestion that the entire structure should be examined with great care.
Watch out: some jurisdictions may have other stair tread nose design requirements and some may prohibit stair tread nose projections entirely. Even in the case of that prohibition, the shape or profile of the leading edge of the step tread remains an important design feature to resist falls.
A stair tread with a sharp rectangular edge may be prone to breakaway falls, especially in wood stair tread designs, while a stair tread with a too-sloped leading edge may contribute to slipping falls on stairways.
Model Stair Construction Code Specifications for Stair Tread Nose Design
2008 New York State Stair Code R3126.96.36.199: Stair Tread [nose] Profile.
Exceptions [to stair tread nose requirements]:
Another Stair Code Example of stair tread nose profile and projection - BOCA 2001.
Another Stair Construction Code Example - BOCA 2001
Reader Question: 5/22/2014 Ian McIlvaine said:
My father-in-law has tripped several times on his stairs and blamed the protruding nosing. He asked me why stairs have nosings and I had to confess that I didn't really know.
I did some research on tripping and protruding nosings and found that the Australian code does not allow open risers or protruding lips/nosings on stair treads precisely because they are a trip hazard for the disabled.
It is interesting, then, that this article mentions that a stair MUST have a protruding nosing of min. 3/4" to max. 1-1/2". Can anyone explain why this is so when such a lip can so easily catch a toe of someone climbing a stair?
Reply: research into the effects of stair tread nose on trip & fall hazards
Ian you raise an interesting and important question. In part the differences in opinion on stair tread design, not just nosing but riser height, stem from differences in how different people climb and descend stairs. Some have argued that as well as differences ascribed to age, physical size and strength, we even step differently ascending than descending stairs.
Though I'm not an ergonomics expert, for several years I have been studying and photographing different people ascending and descending tall stairs in Mexico where the various pyramids give challenging examples of very tall stairs. Indeed hundreds of photo examples themselves show that while there is a wide range of what's comfortable for different people there are very common ways that people place their feet on tread surfaces ascending and descending.
So some researchers opine that tread noses are an important aid against tripping while others may disagree. Here are some helpful stair research citations on the topic.
Balek, Marietta, Pauls, Riazi, and also Cohen specifically discuss stair tread nose designs. Pauls quotes Templer (1992) in a very helpful summary of the concern and of the recommendations about stair tread nose projections as I quote below, followed by Pauls' own conclusions in the Pauls PDF included in the citations I've provided, some careful thought has gone into the debate thus far.
The illustration and comments below are adapated/excerpted from Jake Pauls (undated) PDF on the topic, retrieved 5/22/14 and cited in the references just below.
Pauls explains that this figure illustrates the analysis of the positions (and possible impact or catch or trip hazard points) of the heel of a foot as it pivots off of a home stair tread of varying tread widths (the "run" measurement for different tread nose projections.
To this illustration one would need to add a critical data that I don't see: the riser height. A taller riser changes the possible point of contact, and in the sketch virtually all of the data points appear to miss a typical projecting stair tread nose for a 5/4" thick stair tread or less.
Keep in mind as well that this particular point of study pertains to catching the heel of a show while descending a stair, not the toe of a shoe on ascent. - DF.
Here are Pauls' comments:
I (D Friedman not Pauls) suggest that in assessing stair tread nose designs we must distinguish between falls when ascending a stair vs. falls when descending the stair. In my OPINION, an open riser or a too-large stair tread nose projection seems from my layman observations to increase the risk of a stair fall on ascent by catching the leading edge of a lifting foot or shoe, while, I agree with Pauls that on descent, a too large projection may catch the shoe heel and also cause a fall. But the optimal projection design may be different in avoiding ascending versus descending stair falls as well as the injury risks different in ascent from descent.
Many of these authors also point out a key factor that is hardly an "also-ran" in the discussion: in stair tripping falls can be ascribed the lack of visual contrast between the tread and the riser - something that can be rather obvious at some stairways, particularly single steps between floors where I've personally observed, photographed, and even witnessed stair falls in both ascent and descent.
Keep in mind that for an elderly or disabled person, living in a home with no stairs at all and with careful attention to remove trip hazards such as thresholds, wires, loose rugs, are all important changes.
The previously-hidden danger on the stair treads shown below was that someone, trying to make the stairs more safe, installed rubber stair tread covers that projected past a broken stair tread nose. The stair treads looked fine but someone stepping on the un-supported edge of the stair tread cover simply broke it away and fell down the stairs.
More than one of these rubber/plastic glue-on stair tread covers had a broken nose, probably because the stair tread "skins" were not properly trimmed and sized to fit the tread. If the rubber or plastic "safety tread" on the stair includes a rounded nose covering extension that is not supported by the actual stair tread nose beneath, breakaways like this are likely to occur.
How Does a Damaged Stair Tread Nose Contribute to a Fall?
To understand the role of the nose or edges of stair treads and the importance of a secure stair tread edge that does not break or collapse, look closely at our photo at left.
When ascending stairs and in some cases when descending stairs, the stair user naturally places their foot and their weight at the leading edge of each step - the tread edge or tread nose.
If that stair tread edge or nose is sloped, uneven, slippery, damaged, or worse, breaks during use, a fall is likely.
There are two distinct stair fall cases that may occur due to a defect in the nose or edge of a stair or platform or landing:
Intact stair tread nose breaks away
Watch out: If a stair tread nosing is intact, that is in place, and if when a walker stepson the edge of the nosing that area breaks way under foot ,that event would be likely to cause or contribute to a stair fall. Tread nose breakaway fall accidents can occur in either ascent or descent of the stair though in my experience and opinion people are more likely to put weight on a stair nose during ascent than descent.
Previously broken stair tread nose uneven edges
If the tread nosing was already broken away that condition can still contribute to a fall, though more from the problem of the inconsistency of the tread nose edge - causing an angling of the foot and a possible slip, rather than causing a fall due to the suddenness of collapse of a breaking-away piece of the stair tread or landing supporting a person's weight.
If a building inspector observes damaged stair treads the stairs should be marked as unsafe and access restricted until a proper repair can be made.
The broken stair tread nosing photos above illustrate this hazard found in an art center in New York City - a public space. At above right you can see how a person climbing the stairs might place her weight on the edge of the stair tread nosing - in this case leading to a break and a possible stair fall.
At above left you'll see some pretty nice handrails on both sides of the stairs - features that may help arrest a fall.
Stair tread design research discussing stair tread nosings
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