I am having a problem trying to delete a basement wall. I have tried the hammer with control key, with control and ALT key (experimenting), and with control key and the basement tool but I just cannot delete the basement wall! It just keeps making either holes or the wall to expand. Is this a glitch? What kind of walls are basement walls anyway? I am able to place windows on them no problem (it makes the basement light up) and I have even been able to place doors but when trying to delete a portion of it, no dice! I am able to use the hammer to create hexagonal corners and make the basement hexagonal but the same does not work on the middle of a basement wall. In other words, the hammer seems to be effective only on corners and to change shapes, create holes, or expand a basement wall inside another. I hope that an experienced builder can provide an easy or just effective way of deleting portions or all of a basement wall on one side. Thank you very much for your help. :p

Well, what do I know? After posting this, I went back to my game (frustrated) and decided to try again. This time, I experimented by building a room with the Wall tool right underneath the basement wall I"ve been trying to delete. Then, I went up to the wall section I wanted to delete and after choosing the hammer and pressing control key, I tried to delete it again (it makes an undeline in green as if placing a basement or room on the wall) and it worked!!! Unfortunately, when I was saving, my game closed but it has nothing to do with doing this (Windows update closed everything to install upgrades). So, there you have it. Hope this will help someone else doing crazy building experiments with the basement tool (I built a three level basement and this problem was in the middle level).

Update: Well, the mysterious Gnome of Sims 3 torturous pranks has stricken once again! I went back to the game and could not reproduce the same results with the previous trick. This game can be quite frustrating and weird at times. So, I'm back to square one. Sorry.

Well, simply put, the basement wall does not delete like a normal wall. Rather, the 'square' of basement deletes much the same way you lay out a basement, pool, or anything else.

Well, there IS a way!

Build your basement. Then select the POOL tool and hold down CTRL and drag out a pool shape next to the edge of the wall in the basement you want to delete. Keep holding CTRL. Release mouse when youve outlined a pool next to the wall of the basemet that you want gone. CTRL normally deletes the pool, so it wont actually create one, but it WILL DELETE THE BASEMENT WALL. Again, delete a POOL with CTRL next to the basement wall you want to delete, and that pool does NOT have to exist.

Im aware this topic is very old, it does solve the initial problem. This thread is also at the top of Googles search results for deleting basement walls, so anyone else who stumbles upon this page will have a valid answer on how to do this.