Why do stairs have overhangs?

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


    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?

    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.

    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, 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 https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/8393/2077370.pdf&;ved=0CB0QFjAA&usg=AFQjCNEUyY-IQmZNu3awmH8zfJ7HxQqatw&sig2=LheN5oJyBL3dSc2VJHIUSA" target="_blank">this

    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.

  • tohster

    tohster Correct answer

    6 years ago

    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.

    +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.

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Content dated before 7/24/2021 11:53 AM