Designing Stairs and Steps
Designing stairs is more intricate task than many people realize. And it’s not just about how the stairs look. Proper proportioning is critical to comfort and safety. Set the tread and riser sizes carefully. For I recommend 10″ treads with a one inch nosing. The nosing is the projection forward of the tread beyond the riser below. The riser is the vertical portion of the step. I try to keep the riser height under 7 1/2“, preferring to end up with about 7 1/4″ if I can. We’re all getting a bit older and the fraction of an inch can really make a difference in how a staircase feels. On a house with the now fairly common ten foot ceilings, 18 risers will give you risers of about 7 1/3”. If you have a situation where you want to further reduce the riser height to fit a particular situation or if you have bad knees, you can go by the old “Rule of Thumb” that said the riser and tread dimensions, when added together, should equal 17. So 6 1/2″ risers would be combined with 10 1/2″ treads for maximum comfort. But there are always exceptions to Rules of Thumb, of course.
These riser and tread rules work well for staircases. When we approach a set of stairs, we unconsciously adjust our stride to begin our ascent or descent. But I have found that on interior stairs (or steps) between rooms or in hallways, where there are only two or three risers, people, tend to take the steps in a normal walking stride and will over-step the next tread down if it is too narrow. I have learned that ten inch treads are not wide enough for safety. I had this situation in my own house. I had twelve inch treads shown on the plans and the builder, a good friend and a good builder, mistakenly put in steps with ten inch treads. I let the mistake stand, feeling the cost of the correction was not worth it. But I was wrong. After several people fell, I had to call the builder back in and we changed the steps to the original 12″ treads. No one fell after that, even during parties!
On exterior stairs, I feel 10″ treads are too narrow and 6″ risers are too tall. These stairs may be wet or covered with snow. The lighting might not be as good as indoors. So for outdoors steps, I make the treads 12″ and the risers between 6″ and 7″, with a preference toward the shorter dimension. If you are building a full staircase, say from a deck to the ground below. You can narrow the tread to 11″ and let the riser grow to 7 ¼”.
Have you ever wondered why the nosing is there? Why not simply leave it out and make the steps easier to build? The nosing is actually required by the Building Code to make it safer to go down the stairs. When we step down to the next lower step, the ball of our foot touches first and then the heel goes down. If you experiment with your own foot, you will see that your heel will actually seem to go backward as it goes down. The nosing allows some clear space for your heel to drop. If the nosing was not there, your heel would hit the riser and you would stumble forward. Try filling in the space the tread creates with a book or one inch thick board and then step down the step again. Please hold the handrail for safety. You’ll see how your heel wants to catch on the riser and your loss of balance would pitch you forward.
The real bottom line of all this discussion is to find some steps you feel are comfortable and then measure the treads and risers. If you do this you will quickly learn what dimensions are best for you.
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