# sweating vent stack



## mike gunderson (May 23, 2010)

I am a contractor specializing in remodeling and need plumbers advice. I did a whole house remodel with additions a couple years ago. We are having continual problems with a 3" vent stack condensation problem. It runs up a bathroom wall through the ceiling and then through about 4' of attic area that is insulated but not heated then through the roof. In cold weather there is so much condensation on the outside of the pvc pipe that it is causing alot of ceiling damage. I have wrapped the pipe in insulation, seemed to have no effect. The pipe turns at a 90 degree angle for about a foot above the ceiling before going through the roof. Would this cause any problem? Any suggestions would be appreciated.


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## Tinstaafl (Jan 6, 2008)

Figure out why the pipe is so much colder than the surrounding air and you will solve the problem. I couldn't begin to guess without seeing it.


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## dtsinc (Jan 26, 2009)

The pipe has cold air in it because it comes down the stack from outside. It is common problem here in Montana, and other states that see extreme cold. 
Typically I have the stacks spray foamed from the ceiling to the roof sheating. 
There could be too much humidity in the attic space from excessive heat loss and or improper ventilation.
Is the attic space insulated on the ceiling or at the roof?


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## mike gunderson (May 23, 2010)

The attic space is insulated with spray foam on the roof sheathing. Being in NE Montana myself I know what condensation can do with improper venting. I just never have seen it this bad. There is a bath fan vent in the same area that is vented out the roof. I

t insulated well also. I"m going to check that and make sure the little flapper on the fan itself is not broken or stuck open, I have had that happen and end up with a pipe full of water. Could be moisture coming from there into the space. Thanks


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## dtsinc (Jan 26, 2009)

I figured that's how it was insulated, I see a lot of houses insulated this way here in SW Montana. Most have forced air heat and don't have issues with condensation. The air movement really helps. 

Houses insulated this way are extremely tight, and air movement can be an issue.

I have seen it where when someone takes a shower it fogs up every window in the house. Even with a bath fan. 

Is it heated with electric baseboards or radiant hydronic? If so, maybe there needs to be an HRV unit in the house? 

I would spray foam the vent pipes with enough foam to get past the dew point. Cheapest and easiest option, if you have a local guy.


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