Alteration to an Existing Stair

[MKALLAY]

Good morning,

I have an interesting code question relating to the International Existing Building Code, and wondering if anyone can provide insight.

The scenario involves an existing dormitory building at a private boarding school. The designer wants to modify an existing stairway to provide a landing at primary grade level that will also serve as an accessible entry. Doing this will require removing and reconstructing a portion of the stairway, from the basement level to the primary level, and then from the primary level to the 2nd level. The complication here is that the existing stairway has treads and risers that do not meet the current IBC (10 ½” treads and 8” risers). Constructing the altered portion in accordance with current IBC requirements would present headroom issues.

The designer is pointing to the prescriptive compliance requirements, Section 503.1 has an exception that reads: “An existing stairway shall not be required to comply with the requirements of Section 1011 of the International Building Code where the existing space and construction does not allow a reduction in pitch or slope.” The designer believes this passage will permit him to alter the stair and use the existing dimensions to reconstruct a portion of it. I am not so sure this is the intent of this passage. (My belief is that the portion of stair not changed would be permitted to remain, but any portion constructed new must comply with IBC stairway requirements per Section 1011)

Can anyone offer insight on this? Or perhaps suggest an alternative passage (i.e., anything under work area method?) that would allow the designer to proceed in this manner?

 

[steveray]

If it is being "rebuilt" I do not believe this section would be in play....This section really is about not blowing apart an existing exit enclosure when you remodel....

Doing this will require removing and reconstructing a portion of the stairway,

 

[Paul Sweet]

"This section really is about not blowing apart an existing exit enclosure when you remodel...."

And the framing around the enclosure.

 

[Sifu]

From the 2018 IEBC commentary to 503.1:

The exceptions address issues that arise with stairways.
While not specifically addressed, ramps may
have similar concerns. According to Exception 1, if an
existing stairway was built with a steeper rise/run
ratio than permitted in the current code, the stairway
can be replaced with the existing configuration.
Enlarging the opening to achieve the current rise/run
ratio and headroom would be considered technically
infeasible. The principle is that not allowing for this
option could result in stairways that were not maintained
because they could not be brought up to current
codes.

 

[Wecline1]

In the jurisdictions I have worked, in central California, the rebuilding part would take it out of existing. How would you then maintain the variance of less than 1/4 inch for treads and risers?

 

[Yikes]

I had a project in a major city in southern California where this exact situation occurred. An old stair between first and second floor needed to be replaced. There was no room to make longer treads/shallower risers - - the flight would've encroached into minimum landing lengths.
The city allowed us to completely removed the old flight, and build a new one of identical proportions.

I agree with Wecline 1 that within a flight of stairs you need to keep the same proportions.
For example, if your existing stair is 9" rise, 8" run, and you were replacing 1/2 flight of stair, you wouldn't try and make half of the stairs 7"/11".

 

[MKALLAY]

Thank you to all who have replied - and since my original post, someone has pointed out to me another wrinkle in the IBC that relates to this issue. One of the points of discussion we had with the designer was that while the prescriptive compliance method gives some latitude on alterations to an existing stairway, it did not seem that the work area compliance method offered the same latitude - referring only to IBC for requirements in a new construction element. But then looking more closely, we found that IBC Section 1011.5.2 Exception 4 reads thus: "See Section 503.1 of the International Existing Building Code for the replacement of existing stairways" - so in fact by circular reference we go from the prescriptive path of the IEBC back to the IBC, and then back again to IEBC 503.1. It seems very intentional the folks who wrote the Code want to be sure we get to this passage!

I learn something new about this Code every day!