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Why do I get condensation outside the baffles of my cathedral ceiling?

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I am a licensed contractor in RI .I own a home built in the 1900's, it is a 2 story ,two family house with a gable roof and  full unfinished attic. I am in the process of converting the attic to living space.

I keep ending up with condensation and wet insulation.

( I recently replaced the roof and installed cobra ridge vent along the entire ridge, with the exception of the chimney in the center.

I also cut open the wooden soffits and installed vented vinyl soffit along the entire length of the house, front and back. )

  I recently insulated the rafters of the cathedral ceilings with R-38 kraft faced .

I used styrofoam baffels, every rafter bay, soffit to ridge, front and back.

Before hanging the drywall, while running electrical wiring, i noticed the insulation was wet on one side of the gable. I removed all the insulation and found moisture and mold, outside and inside the baffels. (only on the rear side of the roof)                 I removed everything, treated the mold, let the sheathing dry for apx 2 weeks.

I opened all exterior soffits and removed all the old wooden soffits boards and installed fully vented vinyl soffit pannels

I assumed the condensation was due to improper venting.

After improving the venting, I reinsulated the cathedral ceiling ,fully baffeled, R-38 kraft faced . and within 4 days the condensation returned, this time, only on the outside of the baffels. but only the rear side of the house. (this side gets no direct sunlight)

I do not know what is causing this or how to correct it .

Both front and back of the house are vented the same and insulated the same, the front has no condensation. the back does, even after improving the ventilation.

The roof is a 12 pitch. 2 x 10's   24" oc with cathedral ceilings. There is a very small flat ceiling along the ridge, (about 12")   and knee walls at the soffit end

There are no bathroom exaust vents, venting into the soffit.
asked in Attic Area by peter_lavoie (120 points)
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1 Answer

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Hi Peter,
  1. Is everything open (no drywall on top of insulation) at this moment and you are just working on improving ventilation before the sheathing goes up?
  2. How is your home’s 2nd floor connected to the attic / is there an open passage or a hatch / door which you’re opening and closing periodically?
  3. What kind of a heating system / air circulation system you have in your house? If it’s forced air; how many air supply / return ports you have in the attic area (how big is the attic: … sq feet) / is your furnace big enough to re-circulate air from this additional space.
I believe your moisture and mold problem might be related to your heating system and air circulation since you have just open up this space and created an extra “pocket” for the warm air from the second floor to migrate there (It’s just a thought smiley ).
The main reason for the moisture to appear on the colder side of your attic surfaces is because that warm air will condensate on colder rather than exposed to sun areas, we just have to determine where is it coming from. 
Try to answer my questions, just click “comment” below.
answered by darekrudy (21,730 points)