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Page 25
VERTICAL TERMINATIONS (CONT.)
CATHEDRAL CEILING INSTALLATION
Step 1. Follow installation Steps 1 and 2 under vertical termination section.
Step 2. Using the plumb-bob, mark the centerline of the venting system on the ceiling, and drill a small
hole through the ceiling and roof at this point. From the roof, locate the drill hole and mark the
outline of the cathedral ceiling support box.
Step 3. Remove shingles or other roof covering as necessary to cut the rectangular hole for the support
box. Cut the hole 1/8" (3mm) larger than the support box outline.
Step 4. Lower the support box through the hole in the roof until the bottom of the box protrudes at least
2” (51mm) below the ceiling (Figure 17). Align the support box both vertically and horizontally
with a level. Temporarily tack the support box in place through the inside walls and into the roof
sheathing.
FIG. 18
FIG. 17
Step 5. Using tin snips, cut the support box from the top corners down to the roofline, and fold the
resulting flaps over the roof sheathing (Figure 18). Before nailing it to the roof, run a bead of non-
hardening mastic around the top edges of the support box to make a seal between it and the
roof. Clean out any combustible material from inside the support box.
Step 6. Complete the cathedral ceiling installation by following the same procedures outlines in steps 4
through 8 for vertical terminations.