Used wherever a ceiling support, finish support, or firestop is installed below an open attic. Required to guard against the hazard of blown-in or blanket insulation filling any framed opening or contacting the chimney and possible storage of combustibles against the chimney. Usable for new and retrofit installations. Half cylinder passes easily through ceiling openings between 16′ O.C. joists. Part can be removed without cutting if attic is converted to habitable space and chimney is fully enclosed. Readily trimmed for reduced height installation close to eaves.