I'm talking about the typical situation where a wood door starting to stick in humid weather. I plane the door so that it no longer sticks in the jamb, and then everything is fine until a year later when it gets humid again and the door has expanded yet again and sticks.

I'm a woodworker, and fully aware of the effects of humidity expansion and contraction. I have an end-grain stick cut from the end of a tabletop I built that I measure it's length and use as a gauge to know where in the expansion and contraction cycle the environment is currently in. I always seal all 6 sides of the door in question to limit the magnitude of the expansion and contraction due to humidity.

The thing that I can't figure out is why do wood doors always only grow larger over time? I have numerous doors that I plane to fit very nicely, and then several years later I need to plane again because they have expanded larger. Never in my life have I ever seen a door that shrinks due to low humidity and causes an excessively large gap. I see this on both interior and exterior wood doors.

So what is it about the expansion/contraction cycle that appears to be biased toward expansion?

Ken