[ARCHIVED] Fire alarm but no fire (invisible fire/Fire inaccessible)

Every so often my Sims will be off doing whatever it is Sims do. Watching TV, reading a book, playing in the pool...suddenly I'll get a notification that there's a fire, but...I see no fire? Nobody was cooking, there was no fireplace turned on. Nothing that could start a fire. I have my sims walk through every room just in case I'm blind to it, but they never find the fire.

I can't enter build/buy mode when it does this, and the firefighters are called and they fine me because there was no fire to begin with???

I...?!?? I'm confused.

I don't know if anybody else had this weird thing happen? I have only one mod installed and it's never done this with it installed before.

EDIT: OK...sooooooo
I found the cause. Apparently I had a basement I don't remember building. It keeps catching fire even though there is nothing down there...

My next problem is that I finally go into build/buy mode to demolish the basement...and it says there's nothing to delete. 

I am just as confused as before but now for a different reason...