We made it 4" in www.nachi.org/stairways.htm because a low rise height is a trip/fall hazard (people don’t see it as a step).
You are correct. No minimum rise (R311.5.3.1). A 0" rise would be a ramp 
Short rises are a serious hazard on stairs, people don’t recognize them as a step coming down. I’ve seen some treads intentionally carpeted with very different colors to alert people of a low rises.
I should have looked at my morning emails first:
*Dear Mr. Gromicko:
Re: Minimum riser height of the 2006 IRC
Unlike the 2006 IBC, which has a 4 inch minimum riser height (Section
1009.3, IBC/06), the 2006 IRC does not have any such requirement.
This opinion is based on the information which you have provided. We
have made no independent effort to verify the accuracy of this
information nor have we conducted a review beyond the scope of your
question. As this opinion is only advisory, the final decision is the
responsibility of the designated authority charged with the
administration and enforcement of this code.
Sincerely,
John S. Gonzalez
Technical Staff
INTERNATIONAL CODE COUNCIL
Chicago Dist. Office*
I would say that depends on the tread depth. It’s not really a problem as long as one can descend reasonably comfortably.
I looked it up in the IRC Commentary and it states
“This code establishes that the maximum riser height is 7-3/4 inches. the IRC does not state a minimum riser height as does the IBC, where 4-inch limit is specified.”
As Jeff stated the IRC code itself does not specify a minimum height.
2003 IRC:
However the IRC does reference and use the following ANSI standard for minimum riser height. ANSI A117.1-1998
So your minimum riser height is justified by at least one accepted, and major, standard.
Good then, we’re sticking with 4".
We’re eventually going to come up with a stairway add-on to www.nachi.org/comsop.htm
I believe the UBC addresses it. This may help.
Thanks John. The author of that article is going to review our document.
Here is some more info for you out of the ADAAG.
**
</H4>
Hmmm, I think back to all the natural stone or slate steps with extremly wide treads and have no recollection of tripping , unlike if it was unexpected at an indoor setting.
I think one should take the surroundings into account when reporting.
many issues on this upscale over $1M condo
client busted his nose during the inspection coming out of the kitchen onto the angled landing
Nick, I agree some of these stepdowns are dangerous, there needs to be a way to make them at least visible, especially in dark areas. Since I’m just offering opinions on my observations, I always mention them in my reports as possible trip hazards. If it kills the deal, then there never was much of one anyway. IMO
Agreed.
You are correct that the IRC does not have any maximum riser height, but your change to require a 4" minimum is not legally enforceable…particularly in your home state of Pennsylvania.
The Pennsylvania Uniform Construction Code has amended section R311.5.3.1 of the International Residential Code and replaced it with exception 8 to section 1014.6 of the 1992 BOCA National Building Code and additional provisions of the 1992 CABO One and Two Family Dwelling Code namely:
Pennsylvania Uniform Construction Code Section 403.21 (6)(ii):
http://www.dli.state.pa.us/landi/cwp/view.asp?a=310&q=211697#403.21
The Pennsylvania Uniform Construction Code ***prohibits BY LAW ***it’s stair geometry regulations from being made stricter by local amendment and ***prohibits BY LAW ***previously enacted local codes which required stricter geometry for stairs from being continued or enforced…including riser height minimums.
While a 4" riser minimum might seem like a ‘good idea’, there does not appear to be any empirical evidence to support claims for such a minimum.
As mentioned, safe stairway construction does not preclude risers being less than 4" high, provided the ratio of riser height/tread depth is kept within the limits of a normal human walking ‘pace’, or about 17-18".
"However the IRC does reference and use the following ANSI standard for minimum riser height. ANSI A117.1-1998?
This statement is completely false.
The 2000-2006 International Residential Code does not reference ANY ‘ANSI’ standards regarding stairway geometry or riser heights.
Requiring a 4" minimum riser height is completely arbitrary and without merit.
Ben & Nick:
Ben said in another post
Your are right. It is a good document.
You’re right. Doesn’t come close. But I can’t carry Paige to the inspection in my pocket or briefcase. (Bummer) Good source, but no quick referral method.
Where are the links to the companion checklist and stairway narratives? Can you provide a link to all appropriate documents on the video page? That would be a big plus!
The main reason I use the Stairway Manufacturer’s Document is to give to builders who want to argue with me about interpretation. When I give them that, they usually just shut up and fix it.
When will people realize that the building code is not a design textbook? Stair proportions should be given by the designer, and there are several rules-of-thumb for determining proper stair proportions. It is the designer’s obligation to know which one to use and how to apply it properly. If it left to the builder, the result may or may not be good, even if it meets code.
The most frequently used is Tread + Riser = 17 to 17 1/2 inches. Also used is Tread times Riser = 70 to 75 inches. There are others. However, when the riser is less than about 6 inches, it is sometimes best to elongate the tread dimension, especially on exterior steps. There is some professional judgement involved.
Wow! Looks like somebody got up on the wrong side of the bed this morning!
Actually we are both wrong and both right. Yes, the IRC does not have a specific, printed reference to ANSI A117.1-1998. However the IRC was intended to cover 1 - 4 family dwellings. The IRC concerns itself with accessibility issues (which is what this ANSI standard is about) in a structure with 4 or more dwelling units:
Now if you follow that to the IBC:
So as you can see the IRC does reference the ANSI standard, but again not directly printing the number in the IRC.
I am curious though about your profile. You state you are a “Homebuilder” and a “Building Code Official” in PA. As a proclaimed “Authority Having Jurisdiction” ( see post reference below) why do you feel the need to hide beyond the moniker of “homebild”? Why do you not provide your name and jurisdiction and assume a true authoritative role? Are you here to educate or berate?