Stair tread depth?

I am looking for information on the minimum stairway tread depth. I came across a Carson Dunlop photo and it states 9 to 9 1/4 inches. According to NACHI, 10 inches is recommended. I am not necessarily interested in what code says but stating a safe tread depth to navigate the stairwell safely.

min depths UBC 10" IRC 9"

So I guess you outside of that.

You don’t need to quote the code, but your not going to find any other measurements out there that will say anything other would be OK.

Always go with InterNachi whenever possible.

Opps! Never used this photo before and it is wrong. It should be 9"-11" without the bull nose for tread and rise should be 8" but now this has been reduced to 7 3/4" according to IRC.

It’s wrong all over the place…

Agreed David that is why even looking at the IBC and IRC is not the same. Mistakes are made everywhere that cost peoples lives in minimum building code. That is why whenever possible I find out what InterNachi wants us to put on the report but photos should always be checked with what is current in your area.

Here is the right one

Exactly what I wanted.

You should edit that post and remove the diagram before someone actually uses it.

IRC minimum tread depth is 10 inches nose to nose

Terminology is still inconsistent “Tread width” is side to side. “Tread depth” is front to back, measured from nose to nose and should be 10 inches minimum.

I agree, but didn’t elaborate! Get rid of it.

Man did they get that one wrong but who cares as long as they get the point right. I have never used this one either in a report. LOL
Someone needs to make sure the next InterNachi library set has all the corrections.
I agree with the terminology being wrong.

This is a description that has been argued for a long time.
Stair tread depth is the distance from nose to nose horizontally and can also be described as the run of the stair stringer. That is how it is written in the IRC.

Residential stairs have 10" tread depth.
The 2010 Stairway Manufacturers’ Association Interpetation of IRC 2009 describes it as such also.

Commercial stairs have a tread depth of 11" and a riser height of 7".

One could argue that the tread width is how wide the board is for the stair tread and the stairway width is how long the stair tread is long.
But if that were the case, the board would be 11" wide with a run of 10".

So can we use the stair tread width enterchangablly with the stair tead depth?

Confused now?

The depth of knowledge to understand the **width **of steps needed to satisfy all the peoples shoe treads we meet. This is a way too **deep **for me to comprehend in this thread but am I confused!!! NO Marcel.(8\)

If you want to describe the stair tread width as 10" then the depth of the stair tread wood become 11".
But the width of the stair tread board needed is 11". So which one should I call it?:mrgreen:

Thanks allot Marcel!!! I had it all straightened up but you went and confused me again.:mrgreen:

The 25 rule for stairs applies to most building if I am not mistake.
It has to do with human gait…
2 risers for one tread should equal 25.
That is the builders objective.
Treads are 10’ inches with rise being 7.5’
Again 2 risers plus one treads equal 25’.

Check out NACHI.TV’s online training video for stairs
Downloadable course book included.

Paige Peters 10-minute video on inspecting stairs -

Yes but Keep your eyes in your pocket if you are Married.:shock: LOL

Yea, I’m not.