Determine the location of your stairs by placing one or more stringers against the rim joist that runs around the perimeter of the top of your home's foundation. Use a pencil to mark the locations where the stringers will abut the rim joist.
Drill into and through the rim joist with a cordless drill equipped with a 1/16-inch bit. Drill several holes spaced about 4 inches apart in vertical rows that will be covered by the stairway's stringers.
Access the space behind the joist by climbing under your deck or porch or access the joists from a location in the basement.
Have someone else hold the stringers or completed stairway against the rim joist in its final position. From behind the joist, insert 3-inch wood screws through each of the holes you pre-drilled. Screw through the joist and into the stringer until the screws are flush with the back of the joist.
Mark the location of stringers against your home's rim joist as you would if you were going to screw the stringers to the joists.
Measure the width of the stringers. Purchase one angle bracket for each stringer that is approximately as long as the width of the stringer where it will attach to the rim joist.
Attach the angle brackets to the rim joist by screwing 3-inch wood screws through the pre-drilled holes in the metal surface. Place the brackets directly next to the locations you marked for the stringers in Step 1.
Hold each stringer in place and insert screws through the holes in the other side of the angle bracket. Screw into and through the stringer at an angle that is perpendicular to the screws that hold the bracket to the rim joist.