Hi Zach,
One of the several wonderful things about earth buildings is their ability to moderate, store and slow-release humidity, just as they do with warmth and "coolth."
It's true moisture can be an issue though. One pair of our buildings is very small, just a row of 8-foot-deep rooms, with a greenhouse attached that has an equal or larger
footprint. That greenhouse is used for full-on veggie production all winter, so in there we do get some moisture issues. It rains in the greenhouse in the mornings if you shake the plastic. The rooms are not too too soggy though -- I mean, at least the
books don't get wavy, which I have seen with just normal weather in a normal wood frame house in Cape Cod. The only door that swells and sticks is the north door of the kitchen, where huge pots boil so the condensation is from cooking more than the greenhouse.
Our other houses have a much better ratio, ie a larger footprint of the house than the greenhouse, and the greenhouses are not fully planted to vegetables but to perennials like grapes and flowers with walking space. There is no moisture problem in their attached houses.
With normal-sized earth houses you never get condensation on the walls like you get in a
concrete or other waterproof house in winter. We hardly get condensation on the windows even when we're boiling a big pot or have 25 people laughing and spouting hot air on a January night -- only in our central kitchen where a bathtub-sized pot boils, but not in our private quarters. Conversely, two of our houses have nothing planted in the greenhouses at all, and yet they never have that parched feeling I often got in centrally heated houses in the NE US.
Ooh, maybe I
should write a jenkins-like book but about the marvels of earth houses!