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How to Pour Concrete Steps
Cast concrete steps provide a strong and durable transition between an exterior surface, such as a patio, and the entrance to your home. One of the most confusing questions that arises, however, is the height and depth (front to back) of each step. The answer to this question lies in a few simple calculations that you can use to calculate the rise and run of the unit.
When considering the total run of the unit, local codes often require that the top bearing extend at least 12 inches beyond the door opening. Subtract the width of a swinging door (usually 32 or 36 inches) from the length you measure from the foundation to the outside edge of the steps. If the remainder is less than 12 inches, you may need to modify your plan.
Know the codes before you start planning the steps. If you don’t build them to code, a building inspector can have you rip them out. The codes may also have something to say about the placement of rebar or other reinforcement, as well as the concrete mix you use.
Expect to spend two to three days planning, laying out, and pouring three stages (not including curing time).
STEP 1
Measure rise and run
Measure the rise and run of the site and drive in stakes to indicate where the base of the bottom step will be when poured. Calculate the unit rise and run of the steps and draw a dimensioned sketch.
How to Calculate Rise and Run
Unit height and unit run of treads are the individual dimensions of each riser and tread.
To calculate the rise and run of the unit, first divide the total rise by 7, a standard step height. Round fractional results to the nearest whole number. Then, divide the total increase by that number again to get the unit increase.
For example, here is the calculation for a total rise of 20 inches: 20 inches/7 inches = 2.8, rounding = 3 steps. 20 inches/3 steps = 6.6 inches. In this example, you will need three 6-5/8 inch high steps to go up 20 inches.
Then divide the total run (to the outer edge of the door sweep) by the number of steps to run the unit. 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 seem too long. Adjust the tread depth to 13 inches, a more comfortable measurement, and achieve a total travel of 39 inches.
2ND STEP
Arrange the soles
Arrange the soles 3 inches wider than the treads. Dig the footings to the depth required by codes, pour the concrete and insert 12-inch lengths of 7- to 8-inch rebar into the footings. The top of the rebar should be about 2 inches lower than the finished height of the steps. Let the footings harden, then dig a 4-inch trench between them and fill it with packed gravel.
How to anchor concrete steps
With an underlying grid of 1/2 inch rebar, the cast concrete steps will give you years of low maintenance service. Some local building codes may require that you anchor concrete steps to the foundation wall. You can either drill at an angle into a poured concrete foundation or through a concrete block wall and insert rebar into the holes.
STEP 3
Overview of steps
Using your plan and the actual dimensions you calculated and sketched, draw the outline of your steps onto a sheet of 3/4 inch plywood. Draw the landing line so that it slopes 1/4 inch per foot. Attach a second sheet of plywood to the first, edges flush, and cut around the tread with a jigsaw.
STEP 4
Check for squareness, level and plumb
Using a framing square, make sure the forms are perpendicular to the foundation of the house, set the forms in place and drive support stakes next to them. Make sure the forms are plumb and level with each other, then secure them to the stakes with 2-inch screws. Cut off any part of the stakes above the forms.
STEP 5
Install riser forms
For each step, cut a piece of wood 2x the width of the stair and rip it at the height of the rise of the unit if necessary. Bevel the bottom edge of each riser (except the bottom one) to help the tread float when you pour the steps. Attach the top riser form to the outside of the side forms with three 2-inch screws. Then install the remaining riser forms.
STEP 6
Fasten the straps
Cut angled braces and attach them to the side forms at the front edge of each step. Then drive in 2×4 stakes at the bottom of the braces. Plumb the side forms and attach the spacers to the stakes. To prevent the risers from bowing, drive an 18-inch or deeper 2×4 stake into the ground in front of the steps. Lay a 2×6 on the risers and secure it to the picket and cleats attached to the risers. Secure an expansion strip to the foundation with construction adhesive.
VARIATION
How to build perpendicular steps
Steps can be executed directly from an exterior door or perpendicular to it. Forms for perpendicular treads go together in essentially the same way as the straight treads shown on these pages.
Draw a level line on the foundation to mark the height of the landing. Measure from this line to position the plywood forms for the back and side. Reinforce the forms with stakes, cut beveled risers, hold them level and mark their lower corner on the foundation. Then attach the diagonal brace to the house and foundation and the risers to the cleats. Reinforce the front edge of the risers as you would a straight staircase.
STEP 7
Fill with rubble
To save concrete, time and money, shovel pieces 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 too much rubble as it will make the concrete on the steps too thin.
STEP 8
Add rebar
To reinforce the concrete, bend lengths of 1/2-inch rebar to roughly match the shape of the rubble mound and lay them over the rubble at 12-inch intervals. Wire perpendicular lengths of rebar to the first pieces. Then lift the rebar and support it on dobies or balusters which you wire to the rebar.
STEP 9
Mix and fill with concrete
Coat the shapes with a mold 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 your way up. Tap the sides of the forms and risers with a hammer and poke a 2×4 from top to bottom into the mixture to drive out any air bubbles. Give the concrete enough time to settle between the rubble and add more concrete if necessary.
STEP 10
Edge risers
Run an edger along the inside edge of each riser to round off the front edge of each tread to minimize chipping. If you are going to cover the steps with brick, tile or stone, leave the edges square.
STEP 11
Delete forms
Leave the concrete in place long enough to support its own weight, then remove the risers and finish the concrete with a trowel. Use a step trowel (a drywall corner knife also works) to smooth the corners. Sweep the steps to roughen the surface, allow the concrete to harden, then install the railing. After 12 to 24 hours, remove the side forms and fill the voids in the concrete.
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