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Most stairs (at least here in the US) have an overhang or 'nosing' where the edge of the stair protrudes over the riser:

nosing

I've heard different reasons for why the nosing exists, but I've not been able to find a definitive source. Reasons I've heard are:

  • It provides more space for feet (I'm not sure this is actually true, since it comes at the cost of potentially tripping on the overhang)
  • It makes the stair more visible
  • It somehow improves safety
  • It creates clearance for toes and heels biomechanically

Can anyone show or point to a source which definitively shows why having the overhang is better than not having it?

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  • I assumed it was simply to allow carpeted stairs space for a vertical tack strip and a tight corner to fix the carpet to discretely.
    – Brendon
    May 16, 2015 at 8:32
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    FYI most stairs I've seen in my life have no nosings in France and the UK. There may also be a factor of cultural inheritance to the presence of nosings in the US.
    – Steve Dodier-Lazaro
    May 23, 2015 at 15:01
  • Steve, i think thats right. Building codes also play an important role. For example, the UK building codes recommend no protruding nosings, although they do also provide specifications for protrusions so evidently they are in use somewhere. See this
    – tohster
    May 23, 2015 at 15:12
  • Whatever the reason, I'm glad about it because people are physically larger these days and consequently have bigger feet than they did when stair standards were devised. Also, improvements in rehab have helped people who would otherwise be in wheelchairs walk, and they are less steady on their feet. So the bottom line is we need more space to put our feet.
    – Richard
    Dec 27, 2016 at 19:58

6 Answers 6

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+100

Step size and security

When they are well designed, they seem to prevent more incidents than what they cause. There's a lot of information in Pauls, Jake. "Relating stair nosing projection, tread run dimension, shoe geometry, descent biomechanics, user expectations, overstepping missteps, and closed-riser heel scuff missteps.". I've not found studies that advice to avoid it, although I couldn't find good statistics comparing stairs with and without them neither.

Saving space

You can build stairs using a shorter structure and without losing any space for stepping.

Additionally, if your stairs are already built, you can increase the place for stepping without the need to modify the whole structure. A lot of houses may have been built without taking into account safety standards and usability, then overhangs could help to improve that.

I've made an image to illustrate my point
(Note: Steps dimensions haven't been drawn based on security standards, so don't blame me if your grandma falls down from stairs that were designed based on this image: )

enter image description here

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  • Exactly, stairs are meant to move up, not forward! But it's also about stepping comfort like Jason C points out.
    – jazZRo
    May 17, 2015 at 9:18
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    @rewobs great answer, and although I decided to answer this myself after a lot of research, your paper was the one which unlocked the bibliography I needed to go find the definitive studies. I will see if I can figure out how to award a bounty for your answer here.
    – tohster
    May 22, 2015 at 21:08
  • Note that you can only increase the space for stepping in one direction (up) as the downward 'space' is exactly the same (for every inch you add to the nosing of the tread below, lose one to the tread above. Also note that most people do not go up steps with their heels, so this isn't necessarily a huge advantage.
    – DA01
    May 22, 2015 at 23:29
  • @DA01 I'm not sure about it being totally the same when going downwards, if you're not stepping fast is probable to step like this i.stack.imgur.com/QgTi7.png
    – Alejandro Veltri
    May 24, 2015 at 14:39
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    @rewobs I think that's true on narrow stairs, as is shown in the photo. Narrow, steep stairs were common prior to more universal building codes. Perhaps the nosing is a carry-over from the old days of poor stair designs. :)
    – DA01
    May 24, 2015 at 16:52
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I've not done this before, but I am going to answer my own question because after reading each of the answers here, I found that I needed to dig deeper to find a definitive answer.

Nosings offer multiple usability benefits

staircase schematic

The world's foremost expert on stair design seems to be John Templer, formerly Regents' Professor of Architecture at the Georgia Institute of Technology.

  • He has written many academic papers on stairs, and has published a very detailed book called The Staircase: Studies of Hazards, Falls, and Safer Design. Templer and his book/papers are frequently cited in articles on nosings and staircase design.

  • He says the following about nosings in his book:

    The idea of projecting the front edge of the tread beyond the face of the riser developed long ago. It offers a partial solution to the problem of narrow treads without increasing the overall depth of the tread. It provides, in ascent, extra space for the toe and, in descent, extra space for the heel to tuck in under the nosing projection. Many construction codes in fact require nosing overhangs of 1/2 inch or more, particularly if the going is less than 10 inches. Clearly there is a convincing view that nosings are a necessary safety device, a view supported by a study for the National Bureau of Standards (Templer et al. 1978). For the stairs that were observed and analyzed, it was found that the high-risk stairs (compared to a group of low-risk stairs) had no nosing projections.

  • He goes on in the book to explain that (based on studies) too much nosing can lead to decreased safety, and that a nosing projection that is no more than 1.75cm adds a modicum of safety compared to a flight with no nosing or a flight with larger nosings.

  • Additional articles have also pointed to the visual benefits of nosing. The following report from an Australian industry magazine cites the visual safety benefits of nosings (it also quotes from John Templer):

    Nosings serve a dual purpose on steps: they provide a firm slip resistant leading edge of the step and visually highlight the step edge against the tread and riser surface. The selection of appropriate nosings is integral to maximising safety and visual clarity of a stair flight ... The ADA/ABA advises “Consider providing visual contrast on tread nosings, or at the leading edges of treads without nosings, so that stair treads are more visible for people with low vision”

  • Follow on research on stair nosings has been undertaken by Balek, Marietta, Pauls, Riazi, and Cohen. I'll just highlight the paper which @rewobs cites, and note the biomechanics also supports the use of stair nosings, as the following illustration (from the paper) shows:

    enter image description here

  • Further reading: there is an excellent discussion and bibliography on nosing here.

I'd like to call out @rewobs in particular, who cited a paper in his answer which led me (via bibliography) to this answer.

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  • 2
    +1 for research and pointing out the visual aspects as well as the physical benefits mainly for shallow stairs. Many of the habits of architecture stem from purely aesthetic habits.
    – DA01
    May 22, 2015 at 23:31
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I am afraid my answer might not be considered as the definitive source as I am just quoting someone in a forum but the primary reason is to enable users to walk down steps better by providing more grip and space. To quote the post.

For safety in going down the stairs. When you step down the stairs, you place the ball and toes of your foot on the tread below and then the heel follows. The nosing provides clearance space for your heel to drop on the tread. If there were no nosing, your heel might hit the riser and you will stumble forward (and probably fall if you are not holding n the handrail).

That said, ADA guidelines require that the nosings should be rounded to prevent people from tripping over as they climb up. To quote the guidelines on that

4.9.3 Nosings. The undersides of nosings shall not be abrupt. The radius of curvature at the leading edge of the tread shall be no greater than 1/2 in (13 mm). Risers shall be sloped or the underside of the nosing shall have an angle not less than 60 degrees from the horizontal. Nosings shall project no more than 1-1/2 in (38 mm)

enter image description here

Each stair tread is 11 inches (280 mm) deep minimum with a sloped riser. The nosing shall project no more than 1-1/2 inches (38 mm).

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  • This is what I was taught in human factors grad school as well: the nosing improves safety going downstairs and doesn't significantly impede going upstairs because people don't drag their toes, but they do drag their heels so to speak.
    – illuminaut
    May 16, 2015 at 23:13
  • +1 (I voted a while back). You're right that this doesn't quite provide a clear answer, but there's enough additive information that it deserves the vote!
    – tohster
    May 22, 2015 at 20:18
  • The problem with this theory is that plenty of stairs are built without nosings...namely most any public building with concrete or marble steps.
    – DA01
    May 22, 2015 at 23:27
  • I'm not convinced that the reason is to prevent tripping going DOWN the stairs. It's plausible, but it's certainly not a universal design especially when we talk about masonry stairs. Note that ADA does allow for stairs sans nosing. It's just that if it does have a nosing, it needs to meet some specifications: ada.gov/regs2010/2010ADAStandards/2010ADAstandards.htm (see section 504.5)
    – DA01
    May 23, 2015 at 1:28
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This is conjecture as well but consider this analysis of stair climbing gait, specifically the transition from stage IV (Forward Continuance) → V (Foot Clearance) → VI (Foot Placement):

enter image description here

In particular, note that while lifting the leading foot, the knee flexes more than the hip, thus causing the toes to have a net backwards movement.

If you think of the stair shape as an indentation rather than a lip, what this does is give the climber a full-depth stair to stand on, while letting the stairs ascend more quickly (as in rewobs illustration) and still not getting in the way of the ascending foot which travels around the lip:

enter image description here

So you end up getting a higher slope but still safely accommodate the natural movement of a foot when walking up the stairs and give the climber a full step to stand on.

Another way of looking at it is there's an area of space under each step that the foot does not travel through, so you can extend the step out a bit into that unused space to give a full area to stand on.

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  • What I'd really like to see is both the ascent and descent gaits in ncbi.nlm.nih.gov/pubmed/11809579, but I don't have a subscription.
    – Jason C
    May 16, 2015 at 23:02
  • +1 and Jason, thanks. I also originally thought that the answer might be biomechanical in nature. After further research, it looks like gait is in fact a key part of the answer (see this). I was looking for a definitive answer so I've answered separately and awarded a +100 bounty, but your instincts were correct.
    – tohster
    May 22, 2015 at 21:12
  • The problem with these diagrams is that people don't tend to walk up stairs with their toes hitting the riser. In fact, they tend not to use their heels on the steps much at all (going up).
    – DA01
    May 23, 2015 at 1:29
  • @DA01 The toe path is of more interest.
    – Jason C
    May 24, 2015 at 2:11
  • That's what I'm commenting on. People don't place their toe against the riser on most stairs. The exception would be extremely steep stairs with narrow treads.
    – DA01
    May 24, 2015 at 4:48
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FYI, the overhang is called nosing.

Stair nose is used to create a decorative finished edge on a stairstep or staircase

The primary reason is aesthetics and cost savings--not UX.

Like a door or window casing, the stair nosing covers the seam between two materials meeting--in this case the tread and the riser.

While it may cost more in materials, it's actually cheaper to use trim materials in finish carpentry when you factor in labor.

Stairs are built without this nosing, just as they build caseless doors. However, to achieve this look--though it takes fewer materials--takes much more in labor costs. It's a style used today in some modern style interiors.

enter image description here

When there isn't an issue of the two materials having to be joined (for instance, in concrete steps) then the nosing is typically omitted.

enter image description here

In the case of poured-in-place concrete steps it's also cheaper to omit the overhang as it makes the forms simpler.

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This is a very interesting question. and all the reasons you carried maybe reasonable but nothing related to the toes and heel ... it is all about human comfort.

The comfort space to get you feet onto a stair is 30cm tread X 15cm raise, but the comfort space for your next step average from 26cm to 28cm more than that you will make an extra effort to reach the next step .. see a child when he climb over a stairs he will open his legs more than usual to get the next step.

Man want when he climb a stairs to make his stature raised as possible for his comfort.

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  • Note that what is comfortable isn't a hard-number. It's an inverse ratio between riser and tread. The shorter the riser, the deeper the tread needs to be. gardengatemagazine.com/64stepchart
    – DA01
    May 23, 2015 at 1:32

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