I'd like to understand why wood movement in a floor necessitates large expansion gaps around the outside of the room. I'm not asking why wood as a material undergoes changes due to moisture - I'm interested in how the floor system as a whole actually behaves once installed.
Take for example common wood-strip flooring such as 3/4 oak. Here's a diagram showing a typical recommended installation along a wall parallel to the floorboards:
How is it possible that the entire floor could ever move by approx 3/4" at the walls without being totally destroyed? Nails would be torn out, boards split, etc. if the floor moved that much, no? So is the gap really useful?
(What I would have thought was: given the way boards like this are nailed, the tongues would remain in place relative to the floor, the grooves would slide around, and the floor as a whole would not move at all. Gaps would just open and close between individual strips.)