Potential new build residence with walkout basement. I understand the advantages of insulating a basement in cold climates, but considering the climate in middle Georgia Zone 3, would one not want to leverage the cooler thermal mass of the the subgrade, rather than fight it? I understand it is still vital to air seal, and waterproof, and manage drainage , etc … but was looking at outsulation (either 2″ rigid outside the concrete, or ICF). Just seems a little counter intuitive, no?

Seems that an average ground temp in the mid 50’s can certainly be leveraged to reduce cooling load any time the air temp is above target interior temp of low 70’s (most of the year, and much of it well above), the benefits seems to out weight the winter situation. Even in winter, where lows may be mid 30-mid 40’s, the ground temp again would provide benefit whenever air temp drops below ground temp, no? The only time there would be thermal losses would be when ambient air temp is below target temp, and above ground temp, say 55-73 deg range. (where some heat loss to ground would occur. And that seems like a small percentage of the year. And because the amount of the delta between target and ground temp influences the rate of heat loss, this is the smallest delta region for the annual temperature ranges.

Now then, I understand that if the basement wall is cooler than interior temp, there is the possibility of any moisture in the interior air causing condensation on the cooler concrete wall. But this to be able to managed with proper location/installation of vapor and air barriers, along with the fact that the interior is “conditioned” and as such dehumidified by the HVAC system.

As long as the basement is well designed and built to manage moisture infiltration through the concrete, capillary breaks at footer, and air-sealed to prevent humid air intrusion, I fail to see why one would insulate the below grade portions of a basement, but maybe I am missing something.