That is a popular method, even here. Concrete blocks are used, especially in the warmer, southern part of the country. There are many sites you can look at these if you are interested.
Are you talking about the structural integrity of the rafters? The physics of its integrity is based on the mass and max load for the different building materials.
I studied the discipline "resistance of materials" at the university, I know why a wooden beam and rafters work like this. I just have never seen such use in our area.
I have already seen similar building blocks in our country. Now there are a lot of such "light concrete".
I understand. I can see why the ICF construction would be popular. From what I have read, they work best in warmer climates. I can imagine that they will be very popular in time.
Thanks again for your input.