Need input on stair riser/tread ratios.
Hi All,
I am replacing my basement stairs and have the option of adjusting the treads a bit.
The floor to floor rise is 108 3/4″ and I have up to 120 inches of run.
I planned on using 14 risers 7 3/4″ and initially I figured I would make the treads 9 1/4 (120/13).
I looked in my Building Construction Illustrated by Francis Ching and he has a fairly detailed page with a chart and protractor showing preferred stair angles and riser/tread combinations.
If I use his tables then I would make:
thirteen 8 1/4″ risers to go with twelve 9 1/4″ treads
or
fourteen 7 3/4″ risers to go with 9 3/4″ treads (which I don’t have room for)
I understand the formulas of adding tread to riser and coming up with 17 1/2″. It seems there are a handful of slight variations on this formula and I am hoping someone will tell me that I should either use his numbers and go with the thirteen taller risers so I stick to his ratios/formula OR I should go with 14 shorter risers and not worry about making the treads deviate from the forumula slightly.
I like the idea of a less steep staircase and wider treads but don’t want to build the stairs and find they are awkward or unsafe as I varied from the formula.
If anyone is concerned, I do understand that I am not describing and ideal or code approved staircase. I am rebuilding a basement staircase in a 100+ year old house that has no space to make the staircase any longer.
So do I go for 13 risers and use the formula or do I go for 14 risers and make my treads 1/2″ narrower than the formula?
Thanks,
Karl
Replies
The rise + run = 18" (or some
The rise + run = 18" (or some other near number) rule is a good rule of thumb, but just that. The theory is that the rule corresponds to the average person's stride, and it really does work out pretty well over a range of stair pitches.
There are some other rules -- 2 times rise plus run = 24ish, eg -- that attempt to be a little more accurate. Certainly as you get closer to vertical you want to cut the number down a bit, since a vertical ladder generally has a "rise" of only about a foot.
One very important thing to beware of is getting the treads too narrow. 9 to 9.5" or so should be the limit -- below that and there's danger of having feet slip off the steps.
Always use every bit of run you can get -- even in newer structures it's far too common to find stairs that are too steep.
My personal rule is never, ever, go less than 9 3/4" on treads, as measured nosing-to-nosing - the correct way of measuring treads (not face of riser to nosing). I believe that tread depth of less than that can be dangerous.
While 8 1/4" is code maximum riser height in our jurisdiction under the IRC 2006 NJE I would be less concerned about that than a 9 1/4" tread. Code does permit as little as 9" but I don't agree with treads that short.
Here our NC code allows 8.25" rise and 9" run....
Although I hate building them that way. It happens though when you are building smaller homes with 9' first floor ceilings and use trussed floor systems that are often 14.75" or 16.75" thick. My point is though that your proposed "thirteen 8 1/4" risers to go with twelve 9 1/4" treads" will function fine - although they will feel a little steep. I would almost think it would be expected in a 100 year old house - unless it is the type with 24" diameter x 20' tall columns on the front porch... if you know what I mean....
Or you could go with the 7 3/4" risers and back cut the riser angle to get wider tread which isn't true run but it does help some.
Make sure though that your risers and treads are uniform - all the same size.
Just as important is that you have the correct minimum head height - which should be 6'8".
BTW - Here is a few different flavors of your rule:
The rise times the run should equal approximately 75.
Rise plus run should be between 17" and 18".
Two times the rise, plus the run should equal 25
You don't need to stick exactly to these though... Notice they all incorporate some variance. The idea is just not to have anything crazy like an 8" rise and a 12" run or a 6" rise and a 9.5" run...
BTW - this document: http://www.arcways.com/pdfs/IRC2006.pdf may provide some useful info for you or others reading this.