#1 can you build with cob in colder climates? (SW Missouri)
#2 how thick do the walls have to be?
1. Can and should are two different things. Before the advent of modern insulation cob houses were among the most comfortable because the heat from your fire warmed the wall, and the the thermal mass of the wall kept warming you long after the fire went out. More importantly, unlike brick or log houses which also had relatively high mass, cob houses didn't have a thousand tiny cracks letting cold wind blow through. They were comfortable BUT at the same time they were wasteful because the heat stored in the wall also radiated OUT of the wall at a rate 2-4 times as fast as it radiated in (heat energy moves to colder spaces faster than not-so-cold spaces). Another thing to consider is that in dry climates you can count on it getting reliably warmer in the daytime (even in the winter) and reliably cooling down at night (even in the summer) and the thermal mass of cob tends to absorb free energy from the sun and balance out the extremes of temperatures to help keep us comfortable. In more humid areas you can have weeks go by where it stays cold or hot, and in there cob's thermal mass can work against you, holding on to the heat in a summer night or making you use a lot more fuel to try to keep that extra mass warm through a cloudy cold spell in the winter. Southern Missouri is about as far north as i would ever build a cob house. Our ancestors who built cob houses further north didn't have other choices, and didn't expect to heat their houses to the temperatures we find comfortable. They also built cob walls as thick as 2-3 feet! That is a lot of labor for very little insulative value. My friends who built a cob house in northern Missouri with no insulation were miserable even with a good rocket heater. They just couldn't keep the house warm in the winter. They ended up building a straw bale house. If you like the sculpted lines of a cob house I recommend a cob-bale hybrid, wrapping straw bales with up to nine inches of cob to give you an insulative "ice cream sandwich" of straw and mud. It will be more comfortable and save you a lot of fuel in the long run. Best of luck to you. I would love to see pictures of what you build. I would also be happy to introduce you to our friend Cat Taylor in Texarkana who is building just such a building if you want to see one. You can also meet up with us at the Mother Earth News Fairs in Belton Texas in February or Topeka Kansas in October. Also feel free to follow our adventures on Patreon.com\unclemud where you can support our work if you wish.