Posted on wrong thing first time.  Have cust who claims to have condensation on ceiling in summer time.  has 2 ac... has approx 3,000 sf two story built 1978 mst br is only room with cathedral ceiling.  said the condensation started after they installed ridge vent.  says ceilings are 2 by 6.  i am thinking of removing the dry wall and spray foaming the ceiling and replacing the drywall causing an unvented ceiling.

any thoughts.

Jerry Needham

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Is it the cathedral ceiling that's sweating? Is the condensation on or adjacent to supply vents?

David

Not sure if there are any supply vents in the ceiling.  I am scheduled for an energy audit on June 18th and will know a lot more about the house at that point.  Just trying to get ahead of the curve prior to getting to the house.

Spray closed cell foam and get rid of soffit venting.

Problem fixed! Adding soffit vents just allowed hot moist air to hit, I assume, an underinsulated and non air sealed space. Doubt they actually vented the space with baffels all the way up the cavity to a vented ridge cap. Is there a vented ridge cap?  As the cool air got passed the drywall it just condensed on the nearest surface.

Bet there is a tone of mold on the back side of that drywall. Proceed with caution. Good luck!

Thanks for the reply Daniel.  I have worked with several jobs where we did as you suggest and all seem to be good.  I like the concept of the un-vented foam filled cathedral ceiling.  Cust says no issues with the condensation prior to adding the ridge vent. I know that the moisture hitting the warm ceiling in the summer goes against my training.  I am still going to look at the possibility of too much AC capacity with 2 AC in a 2,600 sf house.  One on first floor and one on second floor.  Lots of un-answered questions at this time.

The problem was probably there before, it just wasn't as apparent - sure rain isn't getting in through said ridge also? Love hot roof systems especially when you have so little room for traditional means - just make sure it is closed cell & I would also test out with a blower door to make sure they got it sealed / installed properly

Sounds like u opened the hornets nest! I would say a 2600 sq ft home shouldn't need more than 2tons a/c depending where u are at. More tonnage can cause issues. Especially makes it difficult for the system to pull moisture out of the air of it is short cycling. I would suggest a duct test to see how leaky the system is. Highly recommend if any ducts are in unconditioned space. Areoseal might be a good option if the leakage is high. I don't really like the stuff but it is a great option

Looks like a leaking ridge vent

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