Permit necessary to build over of your own property in Puerto Rico?

My sister's husband was told that if they build on top of my mother's house they don't need a permit if they build the stairs leading up to it indoors. In others words, cover the stairs so they aren't visible. I'm completely against this. But, I live in Texas so I told her she needs to find more info before doing this. Will someone from the city fine my mother for building without permits? Any info would be appreciated

I'd be more worried about CRIM. Just get the permits and approved engineering plans. If you don't, it could be hard to sell down the road since the bank may not write a loan for the new buyer, especially if the construction affects the hurricane worthiness. And not having an engineered solution could cause a lot of issues. Adding a second floor adds A LOT of weight that wasn't accounted for in the original walls or foundation.