What would cause a plumbing vent stack to condensate?

[TonyB]

Two vent stacks are condensating in my attic . What can i do to stop this. It is causing mold.

 

[HonsellT]

Insulate the pipes.

 

[PaulS]

you can't stop mother nature,condensation comes from hot air transferring to cold air, what you can stop is the living thing, that's the mold, spray it with household bleach. bleach kills mold and stops it from growing in that spot for years.
if you don't want the smell of bleach then home depot sells non smelling, mold killing, spray-able bleach

 

[boyboy]

the stack pipes are condensating because you are running hot water in the home ...its as simple as that ...hot air all ways rises ..so when you drain a bath or a sink as the hot water goes down the pipe the hot air rises and and it hits the cold pipe in loft condensation forms ....lag it ..it will stop

 

[Clayton]

You could wrap pipe in attic with insulation.

 

[david]

The answer is: The type of condensation that you describe is caused when a solid object that is significantly colder that the surrounding air comes in contact with the warmer air and condenses the air, thus removing the moisture from the surrounding air. I am assuming that your vent stacks are made of cast iron, because PVC would not normally form condensation. The solution would be to wrap the pipe in a special type of insulation that is designed for pipes. Check with your local home improvement store. They should have the product.

 

[Joe]

You're seeing condensate on the outside of the plumbing vents? How about other hard surfaces - like the points of the roofing nails on the inside of the roof?

If so, you've got an overall condensation problem, not limited to the plumbing vents. You need more ventilation in the attic space. Add soffit vents under the eaves, and a ridge vent, or some other kind of vent, high on the roof.