Can my husband rent a room out in our jointly owned marital home?

If the home is permitted for rental, the answer is yes. If he is renting it out and the home is not permitted for rental, you might want to consider contacting the County to let them know.

I would suggest that you engage an attorney and also look to the legal separation agreement, or temporary order of the court. Generally in a jointly owned property it would take both parties to agree to rent a portion of the house but you may well have to take this issue to the court.