Things You'll Need
Instructions
Go into Build Mode and select the staircase tool. Scroll through the options and choose a spiral staircase design. Depending on the design of the staircase you choose, it will cost between 800 to 4,000 Simoleons per set.
Use the mouse to hover the staircase over the floor of the house you are modifying. Use the arrow keys to turn it so the front entry to the staircase has enough room for a Sim to walk. Click the mouse once you have chosen the two square by two square spot where you would like to place the staircase.
Click the "Next floor" icon on your control panel to go to the second floor of your house. Place some floor tiling around the top of the spiral staircase if there is not floor tiling already.
Choose the same spiral staircase from Build Mode staircase tool and place it on top of the first staircase to extend it up another floor. Continue doing this up multiple floors until your staircase is as tall as you want it to be, adding floor tiling at each floor level.
Select the fence tool within Build Mode to create railing at the top of your spiral staircase. Choose railing that matches your decor and is medium-sized in height so that it is about waist-high next to adult Sims. Click and drag with the mouse to draw the railing around the top of the stairs, leaving the side where the Sims enter and leave the stairway clear.