Abstract: A frame for mounting devices such as garden windows into the ordinary window frame of a builidng. It includes so-called outer channel members that preferably can surround the garden window and to which the garden window can be secured and inner channel members that are disposed within the outer channel members and are held therein fixedly by screws that adjust their spacing inwardly and outwardly with respect to the outer channel members so that they can accommodate variations in the size, warp, out of square, and the like of the window frames, and also so that they can hold foam material or the like that can seal around the frame to prevent air from passing around the frame into the building.