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Published Dec. 3, 2012

Q: I have to build a simple set of steps but I'm totally lost. I don't understand how to calculate what the distance should be for the risers and the treads. Step building seems harder than using an abacus to do math! Help me understand the thought process of building steps!

A: Building simple steps is a classic exercise in geometry because you're dealing with triangles. The trouble is, infinite triangle sizes are available to you when you go to build a set of steps, and you need to decide which one works best and meets the building code. You bet it can be confusing.

When I say triangles, that might confound, you as the average person sees a flat tread and a vertical riser when they climb steps. But the best way to look at steps is to consider them in a side profile, just like that one photo police take in the booking process after an arrest. Look at a set of steps sideways and place a straightedge on the nosing of the steps and lo and behold you have a series of triangles that touch one another right at the upper and lower tips.

This relationship is important to understand because this is just one aspect of building a set of steps that's safe to go up and down. The human brain is very adept at memorizing exactly how high it needs to lift your leg to just clear the top of each step as you climb up a set of steps. If a riser is too high or even too low from an adjacent one, you'll absolutely trip. The building code permits a minor variance, but I recommend that when you do the math, make sure all risers are equal.

Years ago when I was actively building in the field and having to satisfy my local building inspector, the code stated that the sum of two risers and one tread had to fall between 24 and 26 inches. The code also contained a minimum tread depth and maximum riser height. But even with that, there's an infinite amount of tread and riser combinations. Remember what your math teacher said, there is an infinite number of points on a line.

As a young builder, I did some reading and research and discovered that the sweet spot, and many architects I worked with agreed, was a set of steps that sported a 7.5-inch riser and a 10-inch tread. It just so happens this is right in the middle of the old code requirement as the sum of two of those risers and one tread is 25 inches.

Over the years, I built many sets of stair steps that had that combination, and my customers felt they were the most comfortable steps they had ever gone up or down. But you must make sure this will meet code in your city or town. Don't build them that way hoping they'll pass inspection.

If you can control the height between the two levels the stairs connect, your job of building steps is much easier. I say this because you can find out what your local code requirement is and just make sure that the distance between the two finished floor levels is the exact multiple of the code-approved riser height. Back when I was building this simply meant that the distance between floors was some mathematical multiple of 7.5 inches.

Make sure you have a full grasp of all the other requirements concerning stairs. You have to be aware of headroom, the minimum finished width of steps and the handrail requirements.

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