It all depends exactly where your house is located. Call the Building Department for Clark County at 702-455-3000, and inquire from them... they will be able to forward you to the necessary Building Department, which could be Clark County, or more specifically Las Vegas, Henderson, etc. (even if it's in Las Vegas, it can be at the Clark County Building Department...
I can help with any of your Las Vegas Real Estate needs or questions; feel free to contact me direct.
Mark Fleysher, MBA, Realtor
If you know the builder of the property, then you can inquire with them directly. If you do not know the builder, or if they have gone out of business, then you can follow the information that Mark provided you. If the house was built properly, then the blueprints and other construction documents will be housed at one of the Building Departments.
All plans, structural components (trusses, beams, and hangers) have to be approved by the governing body. I was a structural building components designer, and I am familair with the process here in the Las Vegas Valley.
Have a great day,
Jason Allen Gardner