Just as the title says, does Virginia code require that a manual J be performed for new residential additions regardless of the square footage? If so, please provide citation(s).

Hi all! So today I doing something in the office and dropped something by the return vent. Noticed some light as my wife was downstairs doing laundry. So I did some investigating and found light in all of the return ducts! Not much but after going downstairs and looking I can sort of pinpoint the locations (will be hard to do because of the beams in the way) and see thats where all the duct connections are. Its solid duct but its at the corners and connections. Maybe the size of a pencil eraser, slightly less. All my return vents ducts are located in the unfinished basement and go up to my single floor. Im assuming I should seal these correct? What kind of risk do I pose to my system, if any if I seal them? Also, what exactly are these leaks doing to my system (unfinished side is unheated, and I live in MA for reference?) unsealed? Do I potentially have the possibility to gain airflow out of my supply ducts?!?! Thanks!