Outdoor stairs are built to move between levels of a house or landscaping. Traditionally, exterior stairs on a home are the same width as the doorway they lead up to. Stairs used in landscaping are often wide enough for two people to comfortably walk side by side. Most outdoor stairs use the open riser design. This design calls for significantly less wood, so is more cost-effective. Building an outdoor staircase is a project that can be accomplished in a single afternoon.
Calculate the number of steps needed to span between the two levels of housing or landscaping. Exterior stairs have a rise, or height, of 6 inches, with a 16-inch run or width. This is a more gradual slope than interior staircases, and makes the staircase safer when there is precipitation on the stair surface.
Mark the stair notches on a 2-by-12-inch board to make stringers. Stringers are the support beams for the stairs. They are notched so that tread boards can be affixed to them, and run at a diagonal from the footing to the landing. Use a carpenter's square to mark each notch. Set the carpenter's square so the bottom leg measures the run, and the top leg measures the rise. The measurements should line up with the edge of the board. Use a carpenters pencil to mark cut lines along the outside of the carpenter's square. Repeat this process up the length of the board.
Cut the stringers to the length necessary for your project. The length should be the same as the distance between the footing and the landing. Use a circular saw to cut away the access lumber inside the marks. Trim the end of the board so it sets flush against the upper surface you intend to attach to your stair. Notch the base, if necessary, so the pad or footing sits slightly inside the stringer.
Attach the stringer to the footing and upper structure. Screw an angle iron first into your footing, then into your stringer. Do the same for the upper end, attaching the stringer to the landing. Keep your boards the same distance apart as your stair tread's length. Stringers are often the same width as the door of the home or 32 inches. If attaching to deck floor joists; rather than use an angle iron, drill holes in the joists and stringers and use carriage bolts run through the holes to affix the stingers in position.
Cut 2-by-16-inch boards into short sections to make stair treads. Cut each stair tread the length of your stair case width.
Set the stair treads on the stringers, so the end of the tread is flush with the outer edge of the stringers.
Nail the stair treads into position. Drive 2-inch nails down through the stair tread and into the stringer. Use at least four nails for each step, two at each end.