Poured concrete steps provide a sturdy, long-lasting transition between an outdoor surface, such as a patio, and the entry to your house. One of the more confusing questions that arises, however, is how high and how deep (front to back) each step should be. The answer to this question is found in some simple math you can use to compute the unit rise and run.
When considering the total run of the unit, local codes often require the top landing to extend at least 12 inches beyond the door swing. Subtract the width of an outswinging door (usually 32 or 36 inches) from the length you measure between the foundation to the outside edge of the steps. If the remainder is less than 12 inches, you may need to change your plan.
Know the codes before you start planning steps. If you don't construct them according to code, a building inspector can make you tear them out. Codes may also have something to say about the placement of rebar or other reinforcements, as well as the concrete mix you use.
Expect to spend two to three days to plan, lay out, and pour three steps (not counting curing time).
Measure the rise and run of the site, and drive stakes to indicate where the base of the bottom step will be when poured. Compute the unit rise and run of the steps, and draw a dimensioned sketch.
How to Compute Rise and Run
The unit rise and unit run of steps are the individual dimensions of each riser and each tread.
To compute the unit rise and run, first divide the total rise by 7, a standard step height. Round up fractional results to the nearest whole number. Then divide the total rise again by this number to get the unit rise.
For example, here's the math for a total rise of 20 inches: 20 inches/7 inches=2.8, rounded=3 steps. 20 inches/3 steps=6.6 inches. In this example, you'll need three steps 6-5/8 inches high to climb 20 inches.
Next divide the total run (to the outside edge of the door sweep) by the number of steps to get the unit run. For example, if your total run was 48 inches, here's the math: 48 inches/3 steps=16 inches per tread. However, a tread depth of 16 inches would feel too long. Adjust the tread depth to 13 inches, a more comfortable measure, and make the total run 39 inches.
Lay out footings 3 inches wider than the steps. Excavate the footings to the depth codes require, pour the concrete, and insert 12-inch lengths of rebar 7 to 8 inches into the footings. The top of the rebar should be about 2 inches lower than the finished height of the steps. Let the footings cure, then dig a 4-inch trench between them and fill it with tamped gravel.
Using your plan and the actual dimensions you have computed and sketched, draw the outline of your steps on a sheet of 3/4-inch plywood. Draw the line for the landing so it slopes 1/4 inch per foot. Clamp a second plywood sheet to the first, edges flush, and cut the outline of the step with a jigsaw.
Using a framing square to make sure the forms are perpendicular to the foundation of the house, set the forms in place, and drive supporting stakes alongside them. Make sure the forms are plumb and level with each other, then fasten them to the stakes with 2-inch screws. Cut off any portion of the stakes above the forms.
For each step, cut a piece of 2x lumber to the width of the stairs and rip it to the height of the unit rise if necessary. Bevel the lower edge of each riser (except the bottom one) to make it easier to float the tread when you pour the steps. Fasten the top riser form to the outside of the side forms with three 2-inch screws. Then install the remaining riser forms.
Cut angled braces and fasten them to the side forms at the front edge of each step. Then drive 2x4 stakes at the bottom of the braces. Plumb the side forms and fasten the braces to the stakes. To keep the riser forms from bowing, drive a 2x4 stake 18 inches or deeper into the ground in front of the steps. Lay a 2x6 on the risers and fasten it to the stake and to cleats attached to the risers. Attach an expansion strip to the foundation with construction adhesive.
To save concrete, time, and money, shovel rubble—clean chunks of broken concrete, river rock, or any clean masonry—into the space inside the forms. Pile the rubble higher under the landing than the first step, but don't put in so much rubble that it will make the concrete in the steps too thin.
To strengthen the concrete, bend lengths of 1/2-inch rebar so it roughly corresponds to the shape of the rubble mound and lay it on the rubble at 12-inch intervals. Wire perpendicular lengths of rebar across the first pieces. Then raise the rebar up and support it on dobies or balusters that you wire to the rebar.
Coat the forms with a release agent. Mix the concrete and bring it to the site in wheelbarrow loads. Shovel the concrete inside the forms, starting with the bottom step and working up. Tap the sides of the forms and risers with a hammer and jab a 2x4 up and down in the mix to drive air bubbles out. Give the concrete enough time to settle between the rubble pieces, and add more concrete if needed.
Run an edger along the inside edge of each riser form to round the front edge of each step to minimize chipping. If you're going to cover the steps with brick, tile, or stone, leave the edges square.
Let the concrete set up long enough to support its own weight, then remove the riser forms and finish the concrete with a trowel. Use a step trowel (a drywall corner knife works as well) to work the corners smooth. Broom the treads to roughen the surface, let the concrete cure, then install the railing. After 12 to 24 hours, remove the side forms and fill in any voids in the concrete.
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