That's right. The main protections against fallout radiation are either a solid massive barrier such as several feet of non-radioactive dirt, or distance, or a combination. In the center area [with no windows] of the second floor of a large 3-storey office building would be better than nothing. That might be the men's room.
If one must ingest radioactive substances in the water, air, and food, it won't matter how protected the thyroid is. If one goes outdoors for extended periods of time, it won't matter, it just won't matter after a while.