If you are only adding a layer of shingles, a permit is not required. A maximum of two (2) layers is allowed. Otherwise, you will need to remove all shingles down to the wood sheathing of the roof which requires a building permit and inspections. Also, if you are repairing roof damage or remodeling the roof, you are required to submit for and obtain a Remodel Building Permit and inspections.
Requirements for submitting a permit application