My wife and I built our dream home 3 years ago and some issues have come to light. Our home was built with Nudura ICF foundation to roof line. The walls are 6" concrete with 3" of foam on the inside and outside. The window bucks where done using 2x10 frame on the inside and left the 3" foam on the outside as a thermal break. The issue is with the installation of the windows. The exterior of the house had strapping used around the windows as a nailing flange, however the windows were never secured or shimmed along the window frame because there was nothing to secure the window to. The first 3" of the window was sitting in the foam. So no every window in the house is wrapping from the heat and cold and we are having troubles opening and closing them. What windows are normally used when the window buck isn't the entire width of the wall?

Instead of using new construction windows with a nailing flange, we always used replacement windows. This allowed us to move the window back from the outside of the wall.

Can you secure through the sides of the window into the 2x buck you had installed?

That's how replacement windows are installed, thru holes drilled in the frame.

It seems like there might be more of a problem than only what you are describing. Do you have pics of the inside before drywall/trim? Could there be an issue with the formulation of the PVC?

Pictures would be helpful. What brand, model are the widows? What are they made of? What color? What is the exterior cladding? color? Are the North windows as bad as the South?