I want to replace four fluorescent lights that are under my patio with fans. I removed the lights and it seems that the box is in a 1x3 (the light weighs only a couple of ounces). I am wondering if the code (which Nevada dwellings must comply with) specifies how an electrical box must be mounted and if there are any weight bearing minimums. If so, I can go back to the builder and ask them to remedy the situation.

I'm sure they are not required to replace your light boxes with paddle fan boxes, unless you pre-bought the house and requested the install.

You may have to replace the boxes yourself.