Hello, I'm going to have about 25 feet wide of hardwood flooring that is going to end at an exterior doorway. I know about leaving expansion gaps at the walls but how does this work at a doorway? Is there a space where the flooring can expand-it looks like the flooring will just but right up to the threshold and I am worried about this but maybe it is designed so the flooring can go under the threshold? House was built in 1993. many thanks as always