An interior door rubs against the header. Which is the least likely cause of the condition?

When an interior door rubs against the header, it signifies a misalignment or a change in the door's position relative to its frame. The least likely cause in this situation is that the door was not painted. While it’s true that an unpainted door could be susceptible to moisture absorption (which might lead to swelling), the issue of a door rubbing against the header is more commonly associated with physical changes to the door or its frame rather than its finish.

In contrast, foundation settlement often leads to structural changes that may cause doors to become misaligned, making it a significant factor in such cases. Similarly, a door that was built out of square will not fit properly within its frame, directly leading to rubbing against the header. Swelling due to humidity or moisture can also change the dimensions of the door, making contact with the header more likely. Thus, while the finish may affect the door's integrity, it is less likely to be the direct cause of the rubbing when compared to structural or dimensional issues.