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Forming Stairways

It takes careful planning to build a stairway that is comfortable to walk on. If one step is an inch or so different from the rest, climbing the stairway will be awkward and possibly dangerous. Each step consists of a horizontal run (tread) and a vertical rise (riser). For adults, a riser height of about 7 inches and a tread width of 10 to 12 inches makes for a stairway that is comfortable and safe. Steps leading to a house should be at least 3 1/2 feet wide, preferably wider. For flights rising more than 5 feet, a landing with at least a 3-foot run is desirable. However, a landing beneath an exterior doorway should extend 1 foot on each side of the opening and have a run of 5 feet.

Tools: Tape measure, level, hammer, circular saw, framing square, baby sledgehammer.

Calculate rise and run. Total rise is the total distance that the stairway rises from the ground to the landing. Total run is the horizontal distance covered by the stairway. Individual rises and runs refer to the height and depth, respectively, of each step. The sum of each run and rise should equal about 18 inches. If you want a series of steps with a gentle rise of 5 inches, you should provide runs that are 13 inches deep.

Caution! Check Local Codes - The building codes for your area may dictate such dimensions as the size of risers and treads and the relationship between rises and runs, width, height of sets of steps, landing size, and footing requirements. Check with your local building department to ensure your plans conform—before they are set in concrete.

1. Plan your stairway. To decide how many steps you need, measure the total rise and divide by 7 inches (or whatever individual rise you use). Round off the result to the nearest whole number to get the number of steps. Divide total rise by the number of steps to get the exact dimension of each individual rise. Decide on how deep you want each tread to be (the individual run). Multiply that run by the number of steps to find the total run and, thus, where the stairway will end. The footing at the base of the stairway should be 6 inches thick and extend beneath the frost line. (Check your local codes for the exact requirement.) Construct the forms so there is an expansion joint between the stairway and the walk. To keep rain and ice from gathering on the steps, slope each one 1/4 inch per running foot for the landing and 1/8 inch per tread.

Calculate ramp dimensions. Ramps are useful if you have someone in a wheelchair or if you need to move wheeled equipment regularly. Otherwise, steps are a better choice; walking down a ramp feels awkward. To frame a ramp, simply construct braced forms for the sides. Maintain a constant concrete depth of at least 4 inches, even at the bottom of the ramp. Do not try to feather out the concrete to nothing. For most purposes, it’s best if a ramp does not rise more than 1 foot in 10 feet, a 10 percent slope.

2. Lay out the side forms. On a sheet of 3/4-inch plywood, lay out the side forms by drawing lines showing total rise and total run. When laying out the length of the landing, be sure to allow 1 1/2 inches for the riser forms at the end of the landing. Mark the end of the landing and draw lines establishing the location of the finished treads and risers. For adequate drainage, the landing should slope away from the house at a rate of inch per running foot.

3. Cut and position the forms. Cut both side forms and set them in place at the entry. Use a framing square to make sure they are perpendicular to the building foundation. Check the forms for proper slope and plumb and make sure they are level with each other. Drive supporting stakes into the ground and against the house. Use a baby sledgehammer to support the stakes as you nail the forms to them.

4. Cut and install riser forms. Cut 2x lumber to the correct height and length for your risers. With a circular saw or tablesaw, bevel the outside bottom of each riser, except for the lowest one. Leave about 1/8 inch of each bottom unbeveled for strength. This bevel makes it easier to use trowels to finish the tread after concrete is poured. Install the top riser first and the bottom one last, using at least three doubleheaded nails or screws.

5. Brace the form. Wet concrete is heavy and exerts a great deal of outward pressure on your form. Support the form at all points where it may bulge out when the concrete is poured. Make sure none of the braces will get in the way when it comes time to trowel the treads or the landing. For stairs wider than 4 feet, add a riser support by attaching a 2x6 or 2x8 to a 2x4 stake driven deep into the ground near the center of the bottom form. Anchor pointed cleats to the support and to the riser pieces. To shore up the sidewall forms, drive 2x4 stakes into the ground, then nail 1x4 braces to the 2x4s and to the stakes that anchor the sidewall forms. Nail on a 1x4 cross-tie to support the sidewalls.

Build form for a parallel stairway. To build a form for concrete steps that run parallel to the building, strike a level line on the building wall to establish the landing height. Measure from this line to position the plywood forms for the front and side. For deeper stairs (a greater distance between risers), factor in a 1/4 inch slope per foot. Brace the plywood pieces with stakes. Cut the beveled riser pieces. Have a helper hold the top and bottom risers level to determine the location of the diagonal brace. Attach it to the house, then attach the risers, cleats, and braces.

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