I want to be recessed into the wall with the outside face of window equal to outside face of 6" concrete core. I've worn out the keyboard trying to find this online. The ICF makers ALL talk bucks, but windows come AFTER bucks, and the ICFers don't seem to discuss the after things. If you are siding with wood or fibercement claps it is a totally different story and there are videos and section details and the windows all flange-attach. But this is different. We are thinking of the Marvin Elevate fiberglass frame narrow frame window which is called a replacement window. No 1" frame projection, no flanges. We can use metal straps for fixing them in place. But I need to know about spacing, glueing in foam returns, caulks and sealant details, weeps, etc. And about how to sill, whether a cast stone one, or just bevel the ICF across the bottom.

I did our house without bucks. I didn't want wood around the windows. We used wood to hold foam during the pour but then moved them to use during the second floor pour and after that got rid of them.

I had 1 inch extruded polystyrene (xps) as our "buck" …. We used tapcons to attach the window and did granite window sills. Our windows were InLine fiberglass out of Canada. Us makes crappy cold weather windows. IMHO. The windows had straps like you talk about. The windows were also foamed in place.

Good Luck.

There are certain products (see Nudura End Caps, etc) that offer an EPS bulkhead solution with a fastening strip at the center to allow for attachment point at the center of the wall (if this is what you are referring to?).

First stop should always be your ICF supplier. If they are not able to answer these types of questions (either directly or via their contacts at their respective manufacturer) I would consider shopping around to another distributor. Technical knowledge and support should be available for the entire project, not just setting up and pouring the ICF walls....just my 2 cents (and worth every penny!).