We made the decision to use 1.5” exterior rigid foam after our new house walls were framed so we don’t have the option of expanding our rough window openings and building plywood frames to accommodate our ‘outie’ windows, as described in your article on installing windows over exterior rigid foam. We plan to install vertical cedar siding, and you advised us to use horizontal furring strips for attaching the siding. We are assuming that we can use a ‘retro-fit’ method for installing the rigid foam. There are a few details that we can’t seem to find regarding fastening the windows to the frame and fastening furring strips to window and door framing. Some retrofit diagrams show the rigid foam butting up to 2x framing that has been added around each window rough opening. Other diagrams show the rigid foam extending all the way to the rough opening with the window flange installed and fastened through the foam into the wall framing. Which method do you recommend?

For either of these two methods, we are assuming that we create a 1x blocking/furring frame around the window and fasten our window framing to that. We are also assuming that we install the house wrap over the rigid foam and use current methods for flashing around these windows. Are these assumptions correct?