On Thu, 20 Sep 2007 08:34:26 -0700, Mikepier wrote:

I have to cut off a section of cast iron waste pipe in my attic to tie
in a vent .My concern is when I cut off the section of pipe, the
weight of the upper part of pipe would cause it to possible come
loose from the roof flashing and sink, thus causing a roof leak. The
last thing I want to do is open up a can of worms by doing this job. I
was wondering if I should be concerned or if anyone else has done a
job like this, what advice to offer. Thanks



You didn't state exactly where you are working on the vent pipe. Chances
are you will see very little, if any, movement if you work below existing
vents tied into the main pipe. It would still be a wise choice to secure
the uppermost part of the pipe with strap supports designed to hold pipes
securely.

A reciprocating saw would seem to move the pipe less than doing so with a
handsaw.

I did exactly what you are doing several years back. That vent was cast
iron. I had to cut the pipe in the basement to reroute tub and stool.
There were enough pipes above me to support the vent without moving.

Reflashing or caulking the existing flash when done makes sense.