Any work for hire that cost more than $750 (I think) in materials and labor must be performed by a licensed tradesman.
No, not necessarily. As Royce mentioned, you may need permits and if they are required inspectors will come to check the work. Hence, the work needs to be up to code...IF permits are required.
Please let us know if you have any other questions as we work with many contractors and have done some remodeling ourselves.
Mark & Kari Shea
Shea Real Estate
National Association of Realtors
CA BRE License 01713506