I'm considering building a new door for between the garage and house. My understanding is it needs to be solid wood (or steel) and at least 1-3/8" thick to meet the minimum fire rating. Can you have portions of the door that are thinner than 1-3/8, e.g. recessed panels made from 3/4"? Or is the entire area of the door expected to be 1-3/8" thick? Thanks!