The stairway is a fire exit for a neighboring business, but is on our property. We’re re-doing the backyard, and the business agreed to cover the costs of replacing the stair since they didn’t build the original staircase with permits. However, I’m not sure what needs to be done to start the process.
First place to start would be to visit the city planning/building department to check for any restrictions or special requirements for the area. The second step would be to hire a qualified architect/ engineer to generate a set of plans.
Check with your local building department in your county.