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Stair tread & step construction details & code specifications: this document provides building code specifications for stair treads: sketches, photographs, and examples of defects used in inspecting the step design on indoor or outdoor stairs and their treads, including the requirements for a projecting stair tread nose and the tread nose shape and dimensions.
We discuss the use of color or other visual clues to reduce trip & fall hazards. We also include references to key documents on building codes and stair and railing safety. Our photograph of badly worn stair treads (above) was provided courtesy of Carson Dunlop Associates.
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This article discusses stair tread depth, stair tread nose profile & dimensions or projection, and stairway width.
Stair tread dimensions tread nosings are detailed here. 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. Or see these detailed articles on specifications for proper dimensions for stairs, railings, platforms in our list of Related Topics near the top of this page.
Definition of stair tread (tread depth)
The stair tread is the horizontal walking surface (red arrow) of an individual step. The tread depth is measured from the forward edge of the step nose or edge of the step above out to the leading edge of the step being measured - the space beneath my foot in the photo at left.
Stair risers: A stair riser is the vertical distance (green arrow) between the walking surface of two stair treads is the stair riser or riser height. Open riser stairs have no enclosure (my toe, shown below, would be facing into open space). Closed riser stairs (shown below) include a vertical riser board (that my toe is kicking against). Stair risers are detailed at STAIR RISER SPECIFICATIONS.
Definition of Stairway Width or Stair Width - don't confuse stair width with stair depth
Watch out: it's confusing but many people refer to stair tread depth as stair step or tread width, including our Canadian stair dimension illustration just below.
If you stick to using the word stair tread depth you can avoid this confusion. Oops, that is, unless you start confusing tread depth with stair tread riser height. Stair tread depth is defined above as the horizontal distance from nose to nose or from riser face to nose on open riser stairs.
Stairway width is the horizontal width of the stair opening (blue arrow in our photo). For stairs enclosed by a wall on both sides, usually the stairway width is the distance between those walls.
Stair tread width (green arrow in our photo) is the horizontal left to right width of the stair tread.
At left our photo illustrates three different stair width measurements
Stair Tread Depth (Width) Requirements Vary by Open or Closed Stairway Risers
Closed stair treads using a solid riser are shown at the left of the sketch and open stair treads are shown at the right sketch.
Notice that the minimum stair tread thickness is increased when the stair tread is not supported by a solid riser.
Note that some of these dimensions pertain to Canadian building codes. U.S. stair codes and OSHA stair specifications may vary.
See details on tread specs also found at STAIRS, RAILINGS, LANDINGS, RAMPS
Sketch courtesy Carson Dunlop Associates.
Stair Step Tread Depth, Uniformity & Slope Specifications
The stair treads shown in our photo are very dangerous not only because they are pitched and loose, but because there is danger of stairway collapse.
The tread slope and collapse risk are visually obvious. The stair inspector should be asking: "What caused this weird movement and who made these goofy repairs?" and "What other work did that person perform on this building?"
Stair Riser Height & Stair Tread Depth Dimensions - Example from BOCA Code 2001
My foot illustrates a stair tread depth that is less than 11 inches - the boot toe is against the stair riser and the heel extends well past the stair tread nose.
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. These steps were observed in Barcelona, Spain.
While a tread nose is not required on stairs with open risers, closed riser stairs like these should have a tread nose projection as specified below:
Another Stair Construction Code Example - BOCA 2001
Stair tread nose projection missing or wrong dimension: (falling hazard on descending) or tread nose extends out too far over tread (risk splitting off or trip especially on climbing up).
Broken or Breakaway Stair Tread Nose Hazards & Their Contribution to Stair Falls
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
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.
Effects of Stair Tread Lumber Type on Risk of Damage & Stair Falls
Any broken away or uneven tread nose is a trip and fall hazard. A question sometimes arises about the role of choice of materials in the chances of a stair fall due to tread or tread nose breakage. Does the lumber type of species make much difference in this risk?
Possibly so insofar as treated wood Southern Yellow Pine lumber may present a greater chance of having a breakaway around knots than other choices such as cedar or even plastic wood deck & tread lumber materials.
Nevertheless, the decision to use treated lumber itself should have little useful bearing on a stair fall case as it's both common practice and in some regards is a safer choice to use treated lumber over non-treated pine or SPF since preservative treatments, by reducing the risk of structural rot, should make a wood stairway more durable and safer than more rot-prone choices. .
Most treated wood used in North America is Southern Yellow Pine (SYP) impregnated with preservative salts. The wood is often quite wet with preservative when purchased, it will even squirt when nailed. But since cessation of the use of more toxic wood preservatives (such as CCA), treated wood is not more inherently hazardous when you remove a piece of the tread nose than any other wood, with a small, weak, technical exception. SYP is generally a more knotty wood than some alternatives such as cedar decking.
A property of SYP is its inherent knottiness and tendency to warp. So depending on what alternative and more costly wood that might be use for decking, say cedar, there is a non-quantifiable greater chance that a knot appears at5 or close to the edge of a board and thus could end up on a stair tread nose.
The presence of a knot at the edge of wood used to build a stair tread produces a form of weakness of the wood in that area in that the weight of someone stepping on the edge of the tread nose might break the nosing away on either side of the knot. Openings around knots can also hold water and in a freezing climate an thus contribute to ice or frost cracking and damage to the wood in that area.
Breakaway on either side of a knot in the wood near the edge of the walking surface is what we observe in your video of the area of damaged tread nosing in your video. We haven't established if the break occurred at the time of the fall or prior to it, but I consider it most likely that at least part of the tread nose was broken away before the fall because I observe breakaway of several inches on both sides, left and right, of the knot - not something that would be likely to occur by a single event of a single foot pressure over that area.
Watch out: Builders constructing wooden stair treads using dimensional lumber or 5/4 lumber (deck boards) should take care that the nose of stair treads does not include knots or other damage that increase the risk of a future stair tread breakaway.
What about slipperiness of treated wood decks or stairs when wet? Is treated lumber more slippery than other decking?
The hardness of lumber species varies as does surface texture; cedar (used on more expensive decks, steps, rails) for example has a somewhat more grainy surface and may be less slippery than treated wood when dry.
But I doubt that a coefficient of friction of wet vs dry woods by species has much useful bearing on a stair fall case as it is absolutely standard common practice to use treated lumber on outdoor decks, balconies, stairs, and even railings and balusters.
The really horrible stairs in our photo (left) are installed at a Poughkeepsie NY home surrounded by shade trees. The 2x6 treads (actually 5 1/2" in depth) are exactly 1/2 of the recommended tread depth and are covered with algae that will be hysterically slippery when wet.
And the faux hand railing made of pipe extends just about 20 inches above the stair treads - not a usable rail height. These stairs are treacherous. But we find algal growth can occur on all species of wood used for exterior stairs as well as on some other surfaces, even concrete.
Details about algae, ice, snow, water and other slippery stair and walking surfaces are found at Slippery Stairs, Walks.
Impact of Post-construction Wood Treatments & Preservatives on Exterior Deck or Stairway Slip Hazards
There are other treatments that can be applied to outdoor wood decks, balconies, rails, such as preservative stains (recommended by manufacturers but not required by codes). Such preservatives or stains are used on both treated wood and also on cedar decking, and some paints are also used on synethetic decking. For wood surfaces these add-on products extend the life of the structure, improve its appearance, and many provide some water repellence to the surface - factors that further reduce the chances of formation of slippery algae on the walking surface.
These are the most common causes of slippery stair treads, steps, or other outdoor walking surfaces
See Algae, Ice, Fungus, Wet Surfaces & Other Stair Slip, Trip & Fall Hazards for details. Also see Exterior Stair Falls for a catalog of causes of falls on stairs that includes surface conditions and other defects.
Here we illustrate cases of the presence or absence of visual cues that can inform a walker that she is approaching a step. The use of color to provide a noticeable contrast between the walking surface of a passageway or floor and its steps or stairs can reduce trips and falls for walkers in either direction.
Our photo (left) illustrates a handrail that is indeed "graspable" - a concern in any location, but particularly here at the Metropolitan Opera at an upper balcony where of necessity stairs are angled and steep.
You'll notice that the Met also gives visual clues (a light colored carpet strip) to help walkers discern the location of the stair tread edges.
Lighting Cues to Indicate Steps & Reduce Falls
At Lincoln Center in New York City, these exterior stairs make good use of lighting to reduce the chances of stair trips and falls.
Also see Lighting over Stairs.
Lack of Color, Lighting or Other Visual Clues Increases the Risk of a Stair Fall - Examples
The tile floor shown at below left includes a 4-inch step up into a bathroom. Because the same color tiles were used on the floors at both levels as well as on the step riser, it is very difficult to see that there is a step, especially in low light. In fact the author (DF) tripped on this very step, located in a hotel in Tapalpa, Mexico. We placed a water bottle on the floor to provide a visual clue of the presence of the step riser for our photograph.
Stairs and steps can use a color change or a tile layout change to indicate a change.
In our photo at above left, taken in a restaurant in Rhinebeck, New York, it is still not clear from the upper walking surface whether or not we are approaching a step.
A throw rug or carpet at the top of a stairway is asking for a serious stair fall even if it does provide a color change. This is not a safe way to give a visual clue about the presence of a step.
Do not place slippery items such as a rug or towel on a smooth floor at the top of steps or stairways such as the steps shown in our photo (left).
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Frequently Asked Questions (FAQs) about details of stair tread width, depth, thickness, and tread nose construction & related building and safety codes for stairways.
Question: building code on stair tread relining
I have to skin some new construction stairs, i am going to go over the stairs with a hickory [tread] and was wondering is there a code on tread skins? - Mike
Reply: minimum vs maximum stair tread thickness: needs clarification
Re-covering worn stair treads by installing new treads atop the original ones is a common renovation procedure.
I haven't been able to find a code citation on your question but am still looking and will report here. As you may have noted from the sketches and text above, typically building codes for stairs specify minimum stair tread thickness (1" if supported by a riser at front, or 1 1/2" thick treads if the stairs are open-construction without risers), but they do not specify a maximum allowable tread thickness. . The ADA provides a comparison of stair standards among ADA and other requirements, also with no mention of tread thickness.
Watch out that your new stair skin doesn't create uneven step rise heights at the top or bottom of the stairs, nor a trip hazard at the top landing platform.
Also, let me know what you mean by "construction stairs" as OSHA has some different requirements for stairs depending on their intended use.
Questions & answers on details about exterior stair tread dimensions, construction & related trip & fall safety hazards
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