The 17 1/2 Inch Stair Rule
By Greg Vanden Berge
Here's a simple rule that allows you to build a
comfortable set of stairs. If you can stay within a half-inch of this
simple stair rule, you will find that most of your stairways will be
comfortable to walk up and down.
I'm not suggesting to do this, but I will often walk up and down a set of stairs with my eyes closed for about four or five steps, while holding on to the gripable handrail. If you can do this comfortably, you have what I would consider a comfortable set of stairs in your home. Now I'm not suggesting that anybody walk up and down a set of stairs with their eyes closed.
The 17 1/2 inch stair rule is basically, the stair tread width added to the riser height, should equal around 17 1/2 inches.
Let's say the stair tread width is 10 inches.
And the stair riser height is 7 1/2 inches.
If we add the stair tread width of 10 inches to the stair riser height of 7 1/2 inches we get a stair rule measurement of 17 1/2 inches. This is a very common riser height and tread width and can be found in most residential stairways.
Most of the years I have spent installing stairs, I have noticed that the stair risers are anywhere from 7 1/4 inches to 7 3/4" in height with a 10 inch tread. I have built stairways with a maximum stair rise of 8 inches and a 10 inch tread, this will not be that comfortable of a stairway. It might not sound like much, but if we add the 8 inch stair rise to the 10 inch stair tread we will get a stair rule of 18 inches.
It's hard to imagine that a half-inch difference in the stair rule will make that big of a difference, but it does make a little bit and you can feel it a little more when you start getting farther away from the 17 1/2 inch stair rule. If you have an 8 inch rise you would actually be better off with a 9 1/2 inch stair tread, if possible.
The same thing applies with a 7 inch stair riser, if you have a 7 inch stair riser, I would suggest using a 10 1/2 inch stair tread if possible.
If you are a contractor or carpenter, who builds stairs every once in a while or maybe your a tract home stair builder who builds two do four stairways each day, start paying attention to some of the uncomfortable stairs you walk up and down. Whether you're on the job or visiting some other property, if you walk up a set of stairs that doesn't feel that good, measure the stair tread and riser and add the numbers together.
Do this enough and over time you will find out what I am talking about.
Don't use this formula to argue with your structural engineer, architect, homeowner, contractor, building inspector, planning department or any other person to make a point or change something. If the architect draws a set of plans, you can question him, or see if he even knows about the 17 1/2 inch stair rule, but there's no need to change the world because you have a set of stairs with a 7 inch riser and a 12 inch stair tread.