Safety regulations for irregular stairs

summary: Frequency of use, geometry, and occupant perception are all variables in what defines a “safe ladder”. The user should be careful with irregular stairs such as ship ramps, alternating tread devices, spiral stairs, etc. because they are irregular, which means that their design requirements are considered to be used with caution and frugal. Code expert Glenn Mathewson explains the differences in the code requirements for irregular versus typical stairs when it comes to tread depth, fender height, riser height, and ladder angle, among other rules included in the code.


the stairs An important part of most homes, whether just Few steps from the deck Or a whole trip to the second floor. We use it almost every day with little care. This familiarity and comfort is part of the danger that results in more than one million staircase accidents in the United States each year.

Building codes require ergonomic geometry and consistency between steps to help support the ascent or descent of a semi-conscious occupant of a typical flight of stairs. Stairs are also the architectural focus of many homes, so pushing the boundaries of unique design within predictable geometry is common and supported by the International Housing Code (IRC) with details such as unconventional landing forms (see FHB # 298, Solve problems by going down the ladder) And winder handle, both of which can interlock with standard rectangular surfaces to create a grand staircase. A maximum riser height of 7-3/4 inches and a minimum tread depth of 10 inches are relatively well-known parts of the code, although many countries modify these values ​​slightly.

In general, any drawer inside or attached to the home must comply with the provisions of the code ladder whether the ladder is required by code or simply provided as part of the home’s design. Even if multiple traditional stairs are provided to the same level of the house, they all have to follow the code staircase provisions because the occupant is invited to use any one of them in the same informal way. But not all “stairs” are traditional (more on that in a bit), and there are also exceptions to code stair rules, which are explained in the revision of Section R311.7 in IRC 2021. Stairs that do not lie within or serve a building, balcony, or deck do not need to be compatible with with the section. The same is true for stairs Crawl spaces And attics uninhabitable. Access to these spaces is less frequent and certainly not accidental. Attics and crawl spaces often do not have sufficient height for compatible stairs, and are usually outside the thermosphere, further complicating their access. In general, each of these spaces should have an access hatch, but there are no requirements to access it.

The point at which crawling becomes a file Cellar It’s not clearly defined in IRC, but the code requirements between the two certainly differ. Unlike crawl stairs, stairs to basements must comply with section R311.7. Ceiling height is often the main feature that distinguishes the two, as we expect to ‘crawl’ into the crawl space, and lower floors have the required minimum ceiling height. But the code does not prevent anyone from having a long crawl distance. The “what if” one can imagine never ends, and the code ignores that and handles the possibility.

However, one type of basement ladder shall not comply with Section R311.7, accessed through an external bulkhead enclosure, when the vertical distance from the basement to the outer rung adjacent to the ladder is 8 feet or less – as long as it is not part of Exit required building. This is not found in R311.7 exceptions but in section R311.7.10.2, and has been in the code for some time. Stairs that are not within or attached to a building, deck, or balcony must also not comply with the staircase code provisions. This is for patio landscape stairs or stairs that travel into the courtyard from patios on the grounds. There are many variables of terrain and materials in landscape design, and the environment is unprotected and less maintained. Landscape stairs are not usually used as often as those in or associated with buildings, and are not usually crossed without thinking. These are the stairs where occupants actually expect increased risks. With this concept in mind, there are other types of stairs – some extending the concept – that are also allowed by code that does not adhere to the standard rules of stairs.

Imagine that you are late for work, and you are running down the second floor lobby to the staircase to the front door, but instead of jumping down, skipping every other tread, you reach spiral staircases. Familiarity and comfort fade as you look forward to the steep, narrow descent that wraps up a center column. Your increased interest in each step is the real reason why “less safe” stair architecture is allowed. The maximum riser height for spiral staircases has been increased to 9-1/2 inches and the minimum tread depth reduced to just 6-3/4 inches at the walking line, measured approximately 12 inches from the center pole. IRC’s strict definition of spiral staircases ensures that occupants are aware that they are about to go up or down something that needs their attention. With such attention, a spiral staircase is safe enough to be used as the primary means of exiting any part of the house. Moving furniture to a room on the second floor may not be practical, but the code does not take a stand on this inconvenience.

With the understanding that frequency of use, geometry, and passenger perception are all variables in what defines a “safe ladder,” two alternative types of ladders were added at IRC 2015: rotating tread devices and ship ramps. Alternating tread devices are split lengthwise, with treads at least 7 inches wide that rise higher than those below in an alternating pattern on each side of the ladder. A small tread depth of up to 5 inches is permitted, measured horizontally from the leading edge (notch) on one side to the leading edge of the next tread on the other side of the center split. However, the total depth of your foot space cannot be less than 8-1/2 inches. The remainder of that space is behind the edge of the adjacent tread (but free from the tread directly above). Again, the maximum riser height is 9-1/2 inches.

This geometry can create steep stairs. IRC requires these devices to be between 50° and 70° from horizontal, although you can’t really build a device that reaches that maximum. If you do the math, you’ll see that the maximum angle you can achieve with a 9-1/2-in. height and 5 in. Range is a hair over 62 degrees. Ship ramps carry the same engineering limitations, but the projected tread depth can extend below the tread above.

Riser and tread sizes for irregular stairs

It would be an exaggeration to call either of these stairs, but with consistent geometry and Handrail required, they are close enough to be recognized in the code of finite applications. Like spiral staircases, its lack of resemblance to ordinary staircases greatly increases the awareness of the occupant. People with mobility impairments will not be very quick to approach these stairs, and not using them means complete safety.

Unless another compatible staircase accesses the same area, alternate tread devices and ship ramps are only permitted on mezzanines, lofts, or similar areas of 200 square feet or less and without a bathroom or kitchen to draw people into the space. These restrictions greatly reduce the frequency of their use – another variable in the security equation. The spaces accessible through these stairs are intended to be the second floor areas overlooking a lower level and not as completely enclosed ground levels. They are additional spaces, such as a children’s play area, a sleeping loft, or a reading nook. Going up and down is still needed just as for traditional stairs. Grabable handrails are required on each side, but at a lower height of 30 inches to 34 inches due to the increased steepness of those stairs. Unlike traditional stairs, the space between handrails can be as narrow as 20 inches, since you’ll likely be using both handrails up or down.

There is another “ladder” described in the code, but we all hope we’ll never need to use it. Traditionally, a ladder in a well window more than 44 inches deep was required to service emergency escape and rescue hatches below grade (exit windows). Large boreholes and other attempts to make window wells more attractive stimulated the desire for integrated steps, rather than stairs, to ascend the well. The steps for this design have been recognized since 2000 IRC, but the provisions were further developed in the 2021 version in Section R310.4.2.2. Steps must be at least 12 inches wide and at least 5 inches deep tread. The maximum vertical distance between steps (riser height) is the 18 inches required between stairs.

Code requirements for various stairs are not simple, but their multiples respond appropriately to the changing risks in each design. Rider awareness and where the stairs lead is as part of the safety of the stairs as the stairs themselves. The higher the number of variables, the more precise the code constraints are to the minimum necessary. If the whole house is miniaturized and designed as a small house from IRC appendix Q, there are still more allowances in the design of the stairs.

Glenn Mathewson Consultant and Educator with buildcodecollege.com.

Illustrated by: Kate Francis

Published in Building Beautiful Homes Magazine Issue 304


Related links

%d bloggers like this: