Heatilator BIR42 Owner's Manual page 28

CAUTION! Risk of Fire!
WARNING! Risk of Fire! DO NOT seal area between
ROOM ABOVE (non-insulated ceiling)
B
Ceilng firestop from
bottom
ATTIC ABOVE (insulated ceiling)
Ceiling firestop from
top
Note:
Use same dimensional lumber for framing
ceiling firestop and joists.
A
mm
17
17
A
B
mm
17