Problem

• The interactions use stairs is missing
• My sims takes to stairs to go up but can’t go back down anymore
• My sims can’t use the stairs at all anymore

Cause

• Patch 1.26 made the interaction disappear. As soon as you install Pets, it’s back, but only if you are on the same lot as the stairs.
• Since Patch 1.26, existing spiral staircases tend to be a bit wonkey.

Solutions

• Sims can use the stairs if the interaction is available or not. Just click on a square next to the stairs and they will go up/down.
• In most cases, it’s enough to turn the stairs a little to make them usable again. If you build walls or small stairs, you might need to do some rebuilding. If any of your inactives live in houses with spiral staircases, make sure to check those as well. If Sims can’t use those, that will lead to lags cause they will be trying over and over and over if they are pushed to do something
• If you are using non-EA stairs, make sure to update those.

Mods that help with the issue

• If you only use the patch, you can get this mod to fix the missing interaction Spiral Staircase ‘Use Stairs’ Fix (mod by Shimrod, free registration required)