Flanged windows, where the window frame is attached using a dedicated perimeter nailing flange, are common place in current modern construction, but may be less desirable in high-performance walls. Since the flange must always be at or near the wall sheathing for attachment, the window placement in the opening is constricted and may not align well with the insulation.

It also does not allow for over-insulation of the frame, a practice tat provides significant benefit to the overall thermal performance of the enclosure. High-performance non-flanged windows are likely better suited to highperformance walls, since their attachment method using clips allows for greater flexibility in positioning in the opening.

It is better practice to align the window with the middle of the insulation (in section) to allow better thermal continuity, and over insulate the perimeter frame.