Exit Stair Width - Stringers, Handrails

[mgpxl]

New construction per 2010 CBC.

Required exit width of 68" for steel stairs.

Some conclusions -

a) It is generally accepted that this exit width would be the clear width between stringers.

b) With a 68" req'd exit width, we would have to provide an intermediate handrail.

c) If we were to project the handrails 4" (4.5" max), we would not need to provide intermediate handrail.

d) With a 3" Stringer along the wall, the handrail would need to project 7" from the wall to avoid int.handrail.

Does this make sense or did I skip any steps/misinterpret anything?

Also, if I DO provide an intermediate handrail, would I need to extend the entire landing an additional (11"+12") 23" to provide adequate exit radius?

Thank you!

 

[mgpxl]

Additionally, I see a conflict here with the min. 44" req'd stairway width. If you provide an intermediate for a 6' stair (to satisfy 30" requirement), you reduce either side to 36"...?

 

[George McGerd]

I am not a professional code interpreter, and I don't know much about CBC, but if it is based on IBC principles here are a few things to keep in mind:

1) Generally handrails are allowed to project into your required widths.

2) If you are required by code to have 68" of clear egress width than you will need a center handrail.

3) Keep in mind that in order for stairway width to be counted by code all egress width must be within 30" of a handrail. Therefore, your overall stairway width may actually have to be wider than the required clear egress width to accommodate a center handrail.

4) Based on my experience, center handrails can stop at the end of the stair run and do not need to continue onto an intermediate landing.

5) In addition to the building codes, you will want to check ADA requirements to ensure that your handrails are compliant.

That's my 2 cents. Hopefully it helps ( a little)

 

[mgpxl]

Thank you for your input.

If I were to project handrails 4" on either side, (leaving 60" clear between handrails), this should satisfy the requireme

 

[MA_Architect]

I can't place the source at the moment, but I thought you are only able to count 3" of handrail per side, into your calcs. (Could be a MA issue). Therefore, if you had more than 1-1/2" between the hand rail and wall (assuming 1-1/2" hand rail), then you would essentially have a narrower stair. I hope my explanation was not too confusing.

 

[Paul Sweet]

2009 IBC 1012.8 limits projections into the required width of stairways and ramps at each handrail to 4 1/2".

 

[RLGA]

Exit width for stairs is measured above the handrails. Handrails may project into the required exit width by 4-1/2 inches (2012 IBC Section 1012.8 -- similar requirement in older editions, but different section numbers). Therefore, you can add 4-1/2 inches or the distance to a surface, whichever is less, on each side of a stair.

If the stairway provides 68 inches of required width, and the handrails project 4 inches into the required width on each side, then the clear width is 60 inches, which provides the required 30-inch maximum to a handrail per Section 1012.9 (2012 IBC); thus an intermediate rail is not required.

The minimum 44-inch stairway is to allow two columns of occupants to use the stairs, providing 22 inches per column on each side. This is still tight and will restrict the egress flow of occupants, which is why it has limited capacity. If a stairway has a clear width of 61 inches, requiring the intermediate handrail, the stairs would still only have the ability of handling two columns of occupants, but the flow is less restricted. This allows occupants to move down the stairs much quicker; thus providing a higher capacity, even though the width from the side handrails (including the allowable 4-1/2-inch encroachment) and the intermediate rail is less than the required 44-inch minimum width for a stairway.

 

[tbz]

New construction per 2010 CBC.Required exit width of 68" for steel stairs.

Some conclusions -

a) It is generally accepted that this exit width would be the clear width between stringers.

b) With a 68" req'd exit width, we would have to provide an intermediate handrail.

c) If we were to project the handrails 4" (4.5" max), we would not need to provide intermediate handrail.

d) With a 3" Stringer along the wall, the handrail would need to project 7" from the wall to avoid int.handrail.

Does this make sense or did I skip any steps/misinterpret anything?

Also, if I DO provide an intermediate handrail, would I need to extend the entire landing an additional (11"+12") 23" to provide adequate exit radius?

Thank you!

1. Draw a mark in the middle of the stair flight on the floor
   
2. Then measure 34" to each side to make your required stair width
   
3. Then place your handrails a maximum of 4.5" in to the inside edge on each side
   
4. Thus 68" minus 9" = 59"
   
5. Your stringers need only by more than 59" wide
   

Reason: Once the handrails are installed if you put a level on the inside of the handrails down to the stairs and the stringers are behind this line, then the stingers comply, width is measured above the handrails to min required height. The handrail exception allows everything below to protrude in, look at a set of exterior stairs in open air, if the handrail has balusters and infill from under the handrail molding to the walking surface you would have no problem with it, just because the infill is not there does not mean the exception goes away.

Required stair width and stair tread width are not the same, the code does not say the stair tread width between stringers must be a minimum of "X" inches.

 

[mgpxl]

Your stringers need only by more than 59" wide

Sorry tbz, I assume a typo here, but am having a hard time figuring out what you meant.

We had an issue with another project, coordination issues with structural, where we were forced to cut the top of the stringer and fill the tread to provide exit width. The bldg dept argued that the exit width IS actually the tread width and the 4" projection still needs to maintain the tread width.

It is kind of unclear yet to me -

"1012.8 PROJECTIONS.

....Projections in the required width of stairways and ramps at each side shall not exceed 4 1/2 inches at or below the handrail height."

 

[tbz]

Sorry tbz, I assume a typo here, but am having a hard time figuring out what you meant. We had an issue with another project, coordination issues with structural, where we were forced to cut the top of the stringer and fill the tread to provide exit width. The bldg dept argued that the exit width IS actually the tread width and the 4" projection still needs to maintain the tread width.

It is kind of unclear yet to me -

"1012.8 PROJECTIONS.

....Projections in the required width of stairways and ramps at each side shall not exceed 4 1/2 inches at or below the handrail height."

mgpxl,

No I have no typo and the interp from the others is totally wrong.

Look at this picture below, re read the code section it says projections shall not EXCEED, does not say shall not have. So from the top of the handrail " at or below the handrail height" which is the area from the handrail to the walking surface, projections are allowed.

So the stairwell width is measured above the handrails to the required height. This is an area drawn in space, these lines can't have building elements located in it.

So again from the top of the handrail to the walking surface projections are allowed to reduce the required width of the stairwell.

As long as the stringers are below the top of the handrail and not projecting more than 4.5" in they are allowed to have treads smaller than the required width of the stairwell.

You are looking at drawings when reviewing, not hard to see the end product that needs to be confirmed with inspections.

Now the code does not say projections need to be behind the vertical line of the of the handrails either, but the accepted industry standard is that is the cut off point.

The codes says not to exceed so technically you could have the stringers project in to 4" on each side of the required width and the handrails only 3.5" and thus the stringers are a 1/2" more in than the handrail. But that is not the industry standard, cut off vertical line.

Again like I said in my first post, what is the difference weather you have a handrail with infill and posts or the stringer coming in, the area is allowed to have the stringers there and the treads need not be the full width of the required width.

The maximum allowed project in the code is 4" except handrails, so the stringers would be locked to 4" maximum on each side, and most of the time we are only talking about 2" on each side which is the channel iron size, so why is everyone always making a mountain out of a mole hill.

The code says the projections are allowed! The code says you have to have handrails on stairs!

It's not hard to follow only easy to disagree with what is allowed.

 

[tbz]

Also,

If they get an interp from the ICC or read through the code commentary you will find the simple documentation noting stair tread width is not spelled out in the code as the stair tread shall be a minimum

It is listed to be not less than the landing or door it serves and locked to the minimal width of the stairflight which is measured above the handrails, not at the stair tread.

Stairs and ramps are designed and built to the needs of the egress width.

Thus a ramp needs to be 36" between the handrails, thus a good designer should start there and work out building the guard or walls and then that figures what the minimum width is for your ramp.

The same goes for the stairs. Egress width is required to be 68", handrails project in 4" each side I don't need the center handrail, so we are goo there. Walls 68" plus, stringers behind vertical lines of were the handrails will be placed. treads will be "X" inches wide.

Why people think you need to start with treads need to be 68" wide is beyond me, the handrail placement changes everything.

 

[RLGA]

mgpxl,No I have no typo and the interp from the others is totally wrong.

tbz:

WhileI do agree with your interpretation, I do take exception to the sentence quoted above. One, you do have a typo in your post (your item #5 in post #8), and two, the interpretations by others, including my own, were not "totally wrong." Some were incorrect about the distance of projection and the requirement for an intermediate rail, but I can't see where any of the other guidance was incorrect.

If you think we are still "totally wrong," please enlighten us as to where we are misguided.

 

[tbz]

tbz:WhileI do agree with your interpretation, I do take exception to the sentence quoted above. One, you do have a typo in your post (your item #5 in post #8), and two, the interpretations by others, including my own, were not "totally wrong." Some were incorrect about the distance of projection and the requirement for an intermediate rail, but I can't see where any of the other guidance was incorrect.

If you think we are still "totally wrong," please enlighten us as to where we are misguided.

RLGA, Sorry but I was not talking about your post or the others above on this forum, I was speaking to the interp in the OP replay e-mail which I re-quoted below here.

Bad wording on my part, as I can see why others would think I was ref. the other posts here, but I was speaking of the OP having to cut stringers and extend treads on a previous project were the stringers are located beneath the handrails and in the allowed projections area.

The building dept was totally wrong in their interp.

My Bad

Tom

Quote Originally Posted by mgpxl View PostSorry tbz, I assume a typo here, but am having a hard time figuring out what you meant.

We had an issue with another project, coordination issues with structural, where we were forced to cut the top of the stringer and fill the tread to provide exit width. The bldg dept argued that the exit width IS actually the tread width and the 4" projection still needs to maintain the tread width.

It is kind of unclear yet to me -

"1012.8 PROJECTIONS.

....Projections in the required width of stairways and ramps at each side shall not exceed 4 1/2 inches at or below the handrail height."

 

[RLGA]

tbz:

No problem--thank you for clarifying.