Leza Wang's problem with her door could be the tip of the iceberg. I don't think many people realize the standard metal clad entry doors like Leza's are not completely water tight. If rain is running down the door it is probably leaking into the house at the corners of the threshold.
Two of my neighbors, like myself built our own houses. They are out at the lake in cottage country and were built as retirement homes. In all three cases we were living in the houses long before they were finished.
What all three of us found was the outside doors leaked at the bottom of the thresholds. Not much but you could see the dampness in the plywood subfloor at the edges of the thresholds. If the floor was finished you probably would not see anything. The water would seep in under the finished floor and sit there.
Obviously not a good situation. We installed storm doors and that solved the problem. I still haven't finished the floors in my house and have never seen any leakage since installing the storm doors.
I found the same problem in my sons house. There was no indication of leakage but when you probed around there was water under the vinyl flooring by the threshold. Again the problem was solved with a storm door.
If you have a single outside door without a storm door protecting it, check the area around the threshold after it has been raining on the door or soak the door down with a hose. Water has to be running down the door for the leak to happen.
LdB