Customers often expect better workmanship for decorative concrete. This is especially challenging for steps because they are difficult to install and mistakes are more noticeable to the untrained eye. Doing accurate layout work is the first step to achieve a flawless project.
Using an instrument, such as a laser level, is more accurate than using a handheld level where it’s more difficult to transfer marks. Two- and three-plane laser levels are especially nice for layout work because they make it easy to plot both horizontal and vertical lines. By projecting beams of red light, easily seen in shaded or dark areas, these tools make it possible to lay out risers and treads quickly. In areas exposed to direct sunlight, remote sensors, similar to those used with standard laser levels, pick up elevation and plumb beams. It’s also helpful to use a construction calculator that works in feet, inches, and fractions.
Codes define layout
Steps are regulated by the building codes. The International Building Code (IBC) and the International Residential Code (IRC) both require that riser height not exceed 7 3/4 inches (IRC R3184.108.40.206) but you also should check the local code. As a general rule, don’t plan risers less than 4 inches because people tend not to see them as steps. IRC R311.7.6 also requires that exterior steps not have a pitch more than 1/4 inch per foot (2%). For exterior steps, IRC 3220.127.116.11 requires tread widths no less than 10 inches. Establish tread width by measuring the available horizontal distance of the steps and dividing by the number of risers.
There are many different kinds of steps: parallel ones all the same length, tiered steps with each riser a different length, and cantilevered and curved steps. Whatever the type, it’s helpful to start by marking the form lines on a vertical surface; a foundation wall or the vertical plywood form faces on both ends of the steps.
To start layout work, calculate the number of risers needed by measuring the total vertical drop and the horizontal length of the steps. Divide the vertical drop by the possible number of steps until you find the riser height. Then draw a slope line from the point of maximum step elevation to one tread width beyond the nose of the bottom step. Divide the length of that line by the number of step risers and mark the length on the slope line, locating each step. Draw plum and level lines from each point to plot each step. Measure the pitch down from the nose of each riser to locate the top for each riser form.
Rules aside, steps must look good to the viewer. For example, too many steps in one set may not be as aesthetically pleasing as two groups of steps separated by a walkway. Here are some additional suggestions:
- Don’t make treads too wide. A natural walking stride should be maintained for safety and appearance.
- The IRC doesn’t permit more than a 3/8-inch difference between individual riser heights or tread widths on a set of steps
- Ed Sauter, executive director of the Concrete Foundation Association, Mount Vernon, Iowa, and a practicing architect, suggests four proportioning rules. “It’s hard to make them all work, but meeting three out of four gives you a pretty good stair,” he says.
1. Rise plus run should be greater than 17 but less than 18.
2. Twice the rise plus the run should be greater than 24 but less than 25.
3. Rise times run should be greater than 70 but less than 75.
4. Rise times the square root of the run should be 23.5.
Watch for the next Decorative Concrete column for information about building step formwork.
DOWNLOAD (.xls) Ed Sauter’s spreadsheet to help you work out proportioning for step rises and runs.
Doing External Step Layout Work
There is much to consider when you lay out steps. They must be proportionally right, aesthetically pleasing, uniform and dimensionally correct, and pitch water properly. This downloadable spreadsheet, thanks to Ed Sauter at the Concrete Foundation Association, is designed to help you do the layout work. You are welcome to use it on your next stair project. Please let us know how it works for you.
Proportioning steps accounts for length of stride, typically about 26 inches for outside walking. The rise height must feel comfortable as well, with an average of 6 inches.
In the spreadsheet, there are four proportioning tests listed on the spreadsheet. In rare cases, your rise and run selections can fit within the specified ranges for all four. However, “rise + run” and “2rise + run” are the tests most designers use—architects usually use the 2rise + run test when they design steps.
There are blue and yellow boxes in the spreadsheet: blue for inputting numbers and yellow to see the results. When you input numbers in the blue cells, calculations automatically appear in the yellow cells. Section 1 allows you to consider only rise and run dimensions. Section 2 permits you to add total rise and total step run in order to see how that changes the outcome. Total rise is usually a firm dimension but total run often can be adjusted to meet requirements, so that’s a number you can do “what if” changes to.
Section 3 calculates slope and stair nose-to-nose distance; the number you need for the layout process. The accompanying sketch gives you a visual check on the layout.
We think you will find this spreadsheet (.xls) helpful. But, if you discover ways to modify it to make it more useful, please send us a copy.