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When it comes to commercial stair standards, the International Building Code (IBC) establishes the minimum requirements for stairs to insure a level of safety to the public. Several components are looked at such as stair width, headroom, riser and tread heights.
Note that when looking for residential stair standards, one must look at the International Residential Code (IRC). In this post we will be looking at the code standards related to commercial stairs in accordance with the International Building Code (IBC).
What’s the difference between the IBC and IRC? Be sure to check out this POST.
Section 1011 of the International Building Code establishes the code requirements for stairs that serve an occupied building or space. With that said, let’s get into what those commercial stair requirements are…
COMMERCIAL STAIR WIDTH
Unlike residential stairs per the IRC, where the width is just a given measurement, commercial stair width per the IBC is based on capacity. In order to determine this the code refers us to Section 1005.1, but before we look at this section the code does say that the minimum width shall not be less than 44 inches. The reason for this is that if it is determined per section 1005.1 that the width is less than 44, 44 inches shall be used as the minimum. Now lets look at how the width is calculated.
Calculating Stair Width
Section 1011 refers us to Section 1005.1 to size the width of stair. But what is Section 1005.1? This section explains how to size a portion of a mean of egress system. Remember what was said before? These stair requirements are for stairs that serve an occupied building or space. I stairway can be used as a component of a means of egress. For example if a stairway serves a room as a way of exiting, it must be wide enough to accommodate the number of occupants exiting the space. Section 1005.1 outlines several egressing components, which is a topic of its own to discuss, but you can find the requirements specifically for stairways in Section 1005.3.1.
It states that the means of egress for stairs is calculated by multiplying the occupant load served by the stairs by a factor of 0.3 inch per occupant.
In order to best understand this, let us take a quick look at an example:
A stairway serves an occupant load of 200.
Factor per Section 1005.3.1 is 0.3 inch per occupant.
200 occupants x 0.3 inch per occupant = 60 inches
In this example you can see that the minimum width for this stairway is 60 inches. If it was calculated to be less, such as 40 inches for example, a width of 44 inches must be used since that is the minimum as noted above per Section 1011.
There are a few exceptions worth mentioning. Exception 1 in Section 1005.3.1 allows for a reduction in size when a building is equipped with an automatic fire sprinkler system and an emergency voice/alarm communication system, except for when serving an occupancy group H and I-2.
When a building is equipped with these features the factor used when determining the width for stairs is reduced to 0.2 inch per occupant.
For example if we take the same example above, the calculated width would be 40 inches (200 x 0.2), but of course as stated above a minimum width of 44 inches must be used. But you can see that this exception would result in stairs having a smaller width.
Since we are talking about exceptions, let us go back and take a look at Section 1011. Remember when it was said that the minimum width of a stairway shall not be less than 44 inches? There’s an exception to that. Exception 1 in Section 1011.2 allows for a width of not less than 36 inches when a stairway is serving an occupant load of less than 50. With the above example we had to calculate the stair width, but with this exception you can have the stairway width be as small as 36 inches as long as the occupant load it is serving is less than 50.
Accessible Stair Width
It is important to know that these requirements are for stairs serving as a means of egress. The code does also note that if a stairway is to be considered accessible, such as an accessible means of egress, it must have a clear width of 48 inches. More information about accessible stairs along with a list of exceptions can be read in Section 1009.3.
HEADROOM AND VERTICAL RISE OF COMMERCIAL STAIRS
Headroom for Commercial Stairs
Having proper headroom is another important code requirement. The headroom clearance for commercial stairways measured vertically from a line connecting the edge of the nosing should be no less than 80 inches. This clearance must be maintained above the stairway to the point where the line intersects the landing below to one tread depth beyond the bottom riser.
Vertical Rise for Commercial Stairs
Stairs cannot be continuous without have a landing or floor level that breaks up the flight of stairs. The height limit established by code is intended to provide a reasonable interval for the user so that they may rest on a level surface and to alleviate the negative effects of long uninterrupted flights.
The code establishes a maximum vertical height of 12 feet between landings or floor levels for a flight of stairs. If the distance between floor levels exceed 12 feet, the flight of stairs would require a level landing somewhere in-between to break up the flight of stairs.
COMMERCIAL STAIR RISER HEIGHT AND STAIR TREAD DEPTH
Stair riser heights and stair tread depths should be within the parameters of the code to avoid any potential trip hazards for inconsistencies. A uniform flight of stairs provides a safety factor. Inconsistencies or variations in risers or treads could interfere with the rhythm of the individual using the stairs. Therefore limitations in riser heights and minimum widths for treads is an important rule to follow.
Commercial Stair Riser Height
The code specifies that risers should not be more than 7 inches in height and not less than 4 inches when measured vertically between the nosing of the adjacent tread. Any variation of risers within a flight of stairs should not be more than ⅜ inch of tolerance. Note that dimensions here should be taken excluding carpets, rugs, or runners.
Commercial Stair Tread Depth
As for rectangular stair treads the depth should not be less than 11 inches when measured horizontally between the vertical plane of the foremost projection of the adjacent tread and at a right angle to the tread’s nosing. Again the tolerance between treads should be no more than ⅜ inch.
NOSING AND RISER PROFILE FOR COMMERCIAL STAIRS
Nosing in commercial stairs must have curvature or a bevel of no less than 1/16 inch but not more than 9/16 inch when measured from the foremost projection of the tread. The leading edge of the treads nosing must not project more than 1 1/4 inches beyond the tread below.
Also the risers must be solid and vertical or sloped under the tread above the underside of the nosing above at an angle of no more than 30 degrees from the vertical.
COMMERCIAL STAIR LANDING
Commercial stairways must have a floor or landing located at both the top and bottom of the stairs. The width of the landing must not be less than the width of the stairs it serves. As for the depth of the landing, it shall have a minimum depth equal to the width of the stairway measured parallel to the direction of travel or 48 inches, whichever is less.
For example if the width of a stairway is 44 inches, the landing shall be a minimum 44 inches in depth but if a stairway is 60 inches in width, the landing shall only need to be a minimum 48 inches in depth.
Now when a door opens onto a landing it shall not reduce the landing by less than 1/2 the required width and with the door fully open, it shall not project more than 7 inches into the landing.
Accessible Stair Landing
The code does also note that if a stairway is to be considered accessible, such as an accessible means of egress, it must either incorporate an area of refuge within an enlarged floor-level landing or must be accessed from an area of refuge. More information about accessible stairs along with a list of exceptions can be read in Section 1009.3.
STAIRWAY CONSTRUCTION TYPE
The code requires that stairways be built of materials that are consistent with the types of materials permitted for the type of construction of the building it serves. However this does not include the wood handrails which can be permitted for all construction types.
HANDRAILS FOR COMMERCIAL STAIRS
Unlike residential stairs that only require a handrail on one side, commercial stairs require handrails on both sides. The stairway section of the code refers us to Section 1014 for handrail code requirements which you can read more about at the following link HERE.
Summary of Code Requirements for Commercial Stairs
So this basically sums up the basic code requirements for commercial stairs and their dimensions. Therefore let us recap on the commercial stair code requirements found in the IBC:
- Minimum width for stairways is determined by using a factor of 0.3 inch per occupant for non-sprinklered buildings or a factor of 0.2 inch per occupant for buildings equip with sprinklers and alarms, but shall at no point be less than 44 inches.
- Stairways serving an occupant load of less than 50 shall not be less than 36 inches in width.
- Handrails are required on both sides of a stairway.
- Minimum 80 inches of headroom height clearance for stairway.
- Maximum 12 feet vertical height (rise) for a flight of stairs.
- Maximum 7 inch stair riser height and minimum 4 inch stair riser height.
- Minimum 11 inch stair tread depth.
For more information, see Section 1011 of the 2015 International Building Code for a more in-depth look at commercial stair requirements.
* Reference Source – 2015 International Building Code – [Buy on Amazon]