Legend DV36NG Owner's Manual page 17

The upper half of the flashing is installed under the roofing material and not nailed
down until the chimney is installed. This allows for small adjustments.
6) Continue to assemble pipe lengths.
Note: If an offset is necessary in the attic to avoid obstructions, it is important
to support the vent pipe every 3 feet, to avoid excessive stress on the elbows,
and possible separation. Wall straps are available for this
Purpose.
Galvanized pipe is desirable above the roofline due to its higher corrosion resistance.
Continue to add pipe sections through the flashing until the height of the vent cap
meets the minimum height requirements specified in above diagram or local codes.
Note that for steep roof pitches, the vertical height must be increased. A poor draft,
or down drafting can result from high wind conditions near big trees or adjoining roof
lines, in these cases, increasing the vent height may solve the problem.
7) Ensure vent is vertical and secure the base of the flashing to the roof with
roofing rails, slide storm collar over the pipe section and seal with a mastic.
8) Install the vertical termination cap by twist-locking it.
Note: Any closets or storage spaces, which the vent passes through must be
enclosed.
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