A recessed fixture cover device comprising a plurality of components that may be economically and efficiently packed in an unassembled state for transport and/or shipping and then easily assembled to provide a thermal barrier, a fire barrier, an air barrier, a moisture barrier, and/or an insect intrusion barrier between the recessed fixture and the space immediately above and external to the installed cover device. An embodiment of a cover device may comprise two components that may be assembled to form a right-angled parallelepiped shape that lacks a bottom wall thereby allowing the cover device to be lowered onto and enclose a recessed fixture. One or more complimentary connections between abutting edges of the two components allow the two components to be either quickly assembled for use or disassembled for transport or storage thereby providing a benefit to both construction professionals and do-it-yourself property owners.