pouring a concrete foundation. But only if you did the labor yourself. Those ICFs are spendy. The kicker though is that you end up with like R-50 insulated walls. By taking ICFs all the way to the trusses he’s spending quite a bit more upfront verses framing the walls but where he lives the energy savings will be huge. I have a friend with ICFs to the trusses whose house stays 70 the entire year. They don’t have a/c and his wife gets cold in the summer. Pretty cool.
With how much concrete guys are charging post Covid I wouldn’t be surprised if the ICF route is quite a bit cheaper. Unless those have gone up a ton too