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.
For example:
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.