Do you think that building permits are only for remodels? Not always. Building and safety codes vary from county to county. Some counties require permits for smaller jobs that homeowners can do themselves.
To avoid problems it's a good idea to familiarize yourself with you local building and safety department's website. Often their website can be a good resource not only to check whether you need a plumbing permit but also to check on code requirements. You might find information on there that you didn't know you needed.