The present invention is directed toward a track assembly comprising two nested tracks, an inner track and outer track. The assembly is designed so that the outside width of the outer track is equal to or less than the outside width of the inner track to present a substantially flush external surface for attachment of exterior sheathing elements when the assembly is used in an external wall. The system may further comprise a strap or series of engaging surfaces on the inner and outer tracks that generally restrain the inner track relative to the outer track.