Depends on the class and purpose of the vessel. "Frigate" is a broad term of vessels carrying 28-54 guns. Small frigates of 28-36 guns were your average patrol frigate. 36-44 gun frigates sailed dispatches, convoy escort, blockade duty, etc. The heavy frigates or "cruzers" beat up anything smaller than them and served as fleet lookouts, pickets, raiders, and the backbone for smaller navies who couldn't afford any ships of the line.

A frigates has a single deck entirely devoted to its guns. Depending on length and tonnage and materials, the heaviest guns were on this one designated deck. Now on other designs such as a Razee or a Humphrey frigate (Constitution), the upper deck can be mixed use carrying their lighter armed cannon and is exposed to enemy fire and the elements.

Some people get 4th and 5th rate ships of the line mixed up with the heavy frigates of the US. These have 2 completely enclosed gun decks with the very top deck (spar or weather decks) with smaller 12 pounders or less.

Hope this helps with your question.