The house:
2.5 year old townhouse near Washington DC
Living/Kitchen/Dining room approximately 18' X 36'
Hardwood flooring running in the 18' direction/perpendicular to the length of the room.

The issue:
Every year in the Fall, the hardwood floor opens a gap nearly 1/4 inch across the room in the exact same spot.

Builder response:
This is "normal" seasonal change. The hardwood contractor states that this is common in homes.
They did finally agree to bring in a 3rd party inspector. I would like to have good, well thought out questions ready for them.

About me:
I am an engineer and their answer doesn't sit well with me.
I believe this is a subfloor issue.
I have had numerous homes with hardwood and I have never see an issue like this without other contributing factors (subloor problem, division between home addition, etc...)

Am I missing something? Could this be just a coincidence that it happens in this one spot and the builder is correct??