R. Han, it does not have to be dry. There are cob houses in some of the most wet climates in the world like in the UK. Those houses are 300+ years old too. When you build in a wet climate make sure that the rock wall at bottom of your cob wall is high enough not to get rain splashing up on it from the ground and make sure your roof overhang is at least 18” or half a meter at a minimum. That’s called your hats and
boots. Those can be at big as you need them. I built a 50 foot by 50 foot pole barn over my cob house. So my overhangs are 6ft, 9ft, 10ft, and 15.5ft. Adding bio polymers like horse
poop, fermented cactus juice, wheat germ paste, and in your most extreme areas adding boiled linseed oil will give durability and
water resistant to your exterior plaster. Good luck.
Here are a few recent pics of my cob house. Enjoy.