Generally speaking, a CO is required for any new construction or major renovations to ensure that the structure meets all applicable safety and building codes. However, there may be exceptions for certain types of projects, such as minor repairs or alterations. If your deck is an existing structure that has not undergone any major changes, it may not require a CO.
To be sure, it is always best to contact your local building department and inquire about the specific requirements for obtaining a CO for an existing deck. They will be able to provide you with the necessary information and guidance to ensure that you comply with all applicable laws and regulations.