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Unsafe exterior stair (C) Carson Dunlop Associates Stair Tread Width & Stair Tread Nose Construction Details

  • STAIR TREAD DIMENSIONS - CONTENTS: Stair tread width & nosing design specifications & codes. Stair tread width or dimensional specifications. Stair Tread nose shape & size specifications. Stair Tread Width Requirements Vary by Open or Closed Stairway Risers. Stair Step Tread Nose Projection Requirements & Stair Code Citations. Photographs & Sketches Stair Tread Defects: too narrow tread width, too high tread riser, uneven tread risers. Broken or Breakaway .Effects of Stair Tread Lumber Type & Preservative Treatments on Risk of Damage & Stair Falls. Common causes of slippery stair treads, steps, or other outdoor walking surfaces. Use of Color to Indicate Stair & Step Changes Can Reduce Trip & Fall Injuries
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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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Stair Tread Construction Dimensions, Specifications & Safety Defects

This article discusses stair tread depth, stair tread nose profile & dimensions or projection, and stairway width.

Undersized stair tread depth (C) Daniel Friedman

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.

[Click to enlarge any image]

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 tread depths shall be 11 inches (279 mm) minimum.

The stair tread depth shall be measured horizontally between the vertical planes of the foremost projection of adjacent treads and at right angle to the tread's leading edge.

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.

Don't confuse step riser height (defined above) with stairway headroom - the vertical space between the walking surface of a stair tread and the ceiling or other obstruction overhead (defined further
at STAIR HEADROOM).

Definition of Stairway Width or Stair Width - don't confuse stair width with stair depth

Stairway and stair tread width (C) Daniel Friedman

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

  1. Stair tread width (green arrow) (smaller than stairway width due to side trim boards)
  2. Stairway width (blue arrow) over most of this stairway (nominally 36")
  3. Stairway width near stair top (pink arrow) due to a wall projection (nominally 35")

Stair Tread Depth (Width) Requirements Vary by Open or Closed Stairway Risers

Closed stair treads illustrated (C) Carson Dunlop Associates InspectAPedia.com

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 above was provided and used with permission courtesy Carson Dunlop Associates.

Stair Step Tread Depth, Uniformity & Slope Specifications

Damaged stair treads (C) Daniel Friedman

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

Undersized stair tread depth (C) Daniel Friedman

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.

Stair Step Tread Nose Projection Requirements & Stair Code Citations

Stairs with no tread nose projection (C) Daniel FriedmanDefinition of stair tread or landing nose or nosing

The leading edge of treads of stairs and of landings at the top of stairway flights. - IBC 1002 [14a]

While a tread nose is not required on stairs with open risers, closed riser stairs like these should have a tread nose projection that (for juirisdictions that require stair tread or step noses) are typically as specified below:

Watch out: some jurisdictions may have other stair tread nose design requirements and some may prohibit stair tread nose projections entirely.

Details about the proper design of stair tread nosings in shape & dimensions as well as history, research & stair tread nose hazard discussion are at STAIR TREAD NOSE SPECIFICATIONS

Effects of Stair Tread Lumber Type on Risk of Damage & Stair Falls

Lumber grade markings (C) Daniel Friedman

Opinion: Daniel Friedman.

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. .

Treated lumber information stamp (C) Daniel FriedmanMost 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?

Algae on wood steps (C) Daniel FriedmanMore slippery than what?

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

  1. Snow or ice in areas of freezing climates
  2. Algal growth or on occasion fungal growth on the wood surface, largely affected by the presence or absence of sun exposure
  3. Water improperly directed on the deck or stair surface due to mis-routing of roof drainage systems

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.

Use of Color or Lighting to Indicate Stair & Step Changes Can Reduce Trip & Fall Injuries

Handrail at the Metropolitan Opera is graspable where needed (C) D Friedman

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

Stair trip slip and fall hazard example - using color cues (C) Daniel Friedman

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 & AT EXITS.

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.

Stair trip slip and fall hazard example - using color cues (C) Daniel Friedman Stair trip slip and fall hazard example - using color cues (C) Daniel Friedman

Stairs and steps  can use a color change or a tile layout change to indicate a change.

Stair trip slip and fall hazard example - using color cues (C) Daniel Friedman

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.

Throw Rug as Visual Cue of a Step?

Stair trip slip and fall hazard example - using color cues (C) Daniel Friedman

Watch out: 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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Continue reading at STAIR TREAD NOSE SPECIFICATIONS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see STAIR DIMENSIONS, WIDTH, HEIGHT

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STAIR TREAD DIMENSIONS at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice or see this topic index:

INDEX to RELATED ARTICLES: ARTICLE INDEX to STAIRS RAILINGS LANDINGS RAMPS

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