Cob thermal mass comparison

I was curious how a cob home would perform compared to an earthship style home. Would 2 1/2 feet thick wall retain enough passive solar energy to be effective in heating and cooling situations. Cob appears to be cheaper to finnish a project. I understand a cobb home may not have all the features of an earthship but was looking for insight into how cobb compares. Thanks.

Good questions John. What climate are you in? Wall design and thermal mass are only two small pieces in a very big puzzle. Performance is a keyword and how you define it can help guide the design.

In my opinion, typical cob isnt a great fit for climates that need even a moderate amount of heating. With an average .5 R per inch, a 30" thick wall is still only R15 which is a pretty crummy energy performance level even with the thermal mass benefits.

Those thick walls will also reduce your passive solar heating performance. There is also an argument that thick walls reduce interior living space and increase the price per square foot.

Since I know where this is going, I will get my future reply over with: Thermal Mass walls (without exterior insulation) make the most sense in high desert climates with consistent and wide diurnal temperature swings. Not much population lives in areas like that but the ones that do dont have to worry as much about R value for their walls.